Accepting the Unexpected
` In science, as in life, you have to be prepared to accept what you don't expect, or even think is possible. You never know what you're going to find - thus is the importance of keeping an open mind.
` Sometimes people are even forced to accept what they least expect, as in the case of a friend of mine:
` One night, she was awoken by a plaintive meowing from outside her bedroom window.
` 'Oh, the cat wants in', she thought. So, she got moving in the direction of the window - only to be stopped in her tracks.
` A giraffe's head was peering in from the roof!
` Needless to say, we don't expect to see giraffe heads where we think our cats should be.
` In this case, her cat had gotten hold of a giraffe mask and was carrying it dutifully to his human family, just as he had with assorted toys, leaves, pieces of cardboard and numerous gloves.
` In science, of course, surprises are to be expected and any personal preconceptions are to be criticized if they don't seem to match reality. As they say, there are no 'sacred cows' allowed!
` This is what allows scientific hypotheses (and occasionally full-blown theories) to change as more information is discovered. Mistakes, therefore, can be corrected. After all, part of a scientist's training is learning that that they don't know THE truth - they only know what is likely to be the truth, with the information they have at the time.
` That's why the misconception about the portacaval shunt (which I wrote of in this post) is no isolated incident: Scientists are quite often wrong about things, which is the reason for their peers to both review studies (challenge them with their knowledge) and repeat them (challenge them in 'real life') - there is always a chance that the results were due to an explanation that has been overlooked.
` After all, the first priority of the scientist (and the science-minded person) is to keep up with reality, regardless of what they may personally believe. The knowledge derived from the scientific method is ever-evolving.
` If I may use a quote-within-a-quote from Adam Zeman's Consciousness; a user's guide:In the first place scientific knowledge is always provisional: it is uncertain which beliefs will stand and which will fall during the constant process of revision. As the Oxford physician Sir William Osler warned a group of newly qualified doctors at the turn of the century: 'Gentlemen, I must tell you that half of what you have been taught is wrong, and we don't know which half.'
` So true! It is easy to be wrong, largely because it is easy enough not to see alternative explanations. One famous and easy-to-grasp example is the horse named Kluge ("Clever") Hans.
` A hundred years ago, a German schoolteacher presented a horse that appeared to have learned reading, spelling and arithmetic! Notably, every time Hans was presented with a math problem (either verbally or written), he would tap his hoof a number of times.
` Eighty-six percent of those times it was the correct answer. Clearly, this could not be explained by chance!
` Enter the psychologist Oskar Pfungst. He determined that yes, it was not a trick; Clever Hans' trainer was not perpetuating a hoax. Indeed, Clever Hans could get the correct answer even when the trainer was not around!
` One might expect that since the horse really could get the answer right, and that it had nothing to do with signaling from his trainer, then he must really understand math problems! This is the proposed explanation (or hypothesis) held by a lot of people of that time.
` But what about a less obvious possibility?
` Pfungst also found that when the person asking Hans a question did not know the answer, or if Hans could not see the questioner, he would continue tapping his hoof after the correct number had been reached.
` From this, Pfungst managed to work out what was going on; when someone asked the horse a question, they subconsciously leaned forward to a barely-perceptible degree. The horse then tapped his hoof until the correct number was reached, upon which the questioner leaned back, cuing the horse to stop.
` Even when made aware of it, Pfungst still couldn't stop himself from leaning slightly - apparently it is too great a reflex!
` In that way, our intuition can lead us into believing in the strangest and most wonderful ideas, even when they aren't true. While human intuition is useful, it is also what makes a magician's illusions seem so mystifying!
` Similarly, just as Hans' ability to answer correctly could not be separated from his being able to see people who knew the answer, experiments involving alleged psychics show very much the same type of thing.
` For example, people who say they can psychically 'read' someone must be able to see or hear the person - or even someone who is familiar with them; already know something about the person themselves; or at the very least, make extremely vague statements lest they wind up miles away from the mark!
` In fact, you can even deliberately mislead these people by reinforcing any kind of nonsense that you tell them, or that they guess, about your life! However, I think I'll save the details of conscious - and even subconscious - cold reading for another day.
` What really gets me is that subtle cues (as well as obvious ones) are not only used by horses and charlatans; they can easily fool the ordinary person into believing that they have psychic abilities themselves!
` In fact, this very same thing was constantly happening with myself as a teenager. Much of it had to do with avoiding my sadistic and mentally ill father, who would unpredictably and severely punish me on a whim. This was one of many reasons I could generally be found as a wide-eyed, twisted heap of taut muscles and tendons, collecting cobwebs in a corner or scuttling out of sight.
` Needless to say, avoiding him at all costs was imperative. So, I developed the amazing ability of predicting that he was about to head towards whatever room I was in. I didn't know how I did it, but somehow I learned that whenever I would feel a deep panic and start sweating, that meant I had thirty seconds to either get away or look half-dead so he wouldn't bother me.
` This is why I suspect that I was subconsciously hearing some kind of cue in his footsteps - even when I was unaware of hearing anything at all - which, by association with his approach, filled me with terror. Puzzlingly to me at the time, this often happened when I could hear that he was standing relatively still. I can guess that it probably had something to do with the way he shifted his weight.
` Since I couldn't explain where my 'gut feelings' were coming from, I figured that they were some kind of psychic ability. So, I read a lot of library books on the subject and found that I could relate to the people who wrote about their experiences. Not only that, but I 'discovered' that I had a few more 'psychic abilities' as well!
` So, for a while I was a firm believer in these things, heedless to anyone's logical arguments, until I properly learned about the scientific method and fully understood its emphasis on not jumping to conclusions.
` One of many examples of this is the 'staring' experiments by Rupert Sheldrake, who declared that the feeling of 'being watched' by a hidden observer is a psychic ability. Indeed, his results showed that participants had a lot more than a 50% chance of guessing whether or not someone out of view was looking at them.
` This would be amazing if his testing sequences were also random, thus giving his subjects a 50-50 chance of being correct. In actuality, there are noticeable patterns in the sequences he used: A lot more alternations (A, B, A, B, A, B) can be found in his sequences compared to other possibilities (A, A, A, B, A, A) which would normally occur in equal proportions in a truly random sequence.
` Such were the findings of Colwell, Schroeder and Sladen (2000): To see just how much these testing sequences had to do with Sheldrake's results, they did a couple of experiments to see if they could separate the sequences from positive results.
` Here's what they did:
` In the first experiment, they had seven men and five women (all believers in the 'staring effect') in a room by themselves where they sat with a one-way mirror to their backs. Meanwhile, someone else was behind the mirror, staring at them, or not, according to Sheldrake's sequences of 'staring' and 'not-staring'.
` Each participant was given buttons to press for indicating whether or not they felt like they were being stared at. For the first sixty trials of this experiment, they were given no feedback whatsoever as to whether or not their responses were correct.
` For the rest of the trials - 180 more of them - they were shown the words 'correct' or 'false', depending on their success at guessing.
` In the sixty no-feedback trials, everything went as predicted - the average guess fell almost exactly on the mean chance expectation. However, in the trials with feedback, they quickly became more and more accurate, until their guesses were far above chance!
` Why? Since Sheldrake's sequences were not random, the participants could use the feedback - if subconsciously - to catch onto the fact that there are a lot more alternations in the sequence than chance would allow.
` Put another way, the participants learned to switch their guesses most often to 'not-staring', after being told that the previous trial had been 'staring', and vice-versa (even if they had not guessed the previous trial correctly).
` Of course, a believer in Sheldrake's hypothesis could easily say that the real (and least simple) explanation for the improvement is simply because the subjects became more sensitive to their psychic ability.
` Fair enough.
` So, in their second experiment, the researchers took some random sequences of their own, analyzed them to make sure they were really random, and then tried those out on the same participants.
` Plus, to make it as easy as possible for them to use their 'psychic abilities', the subjects knew if they had guessed correctly or not in all of the trials! But, with no pattern to learn, they were unable to do better than chance. Their alleged ability 'disappeared!'
` So there you have it - apparently Sheldrake's non-random sequence is what had influenced the outcome of his 'staring' experiments. In other words, his hypothesis has been falsified.
` And yet, Sheldrake continues to believe in his results and encourages other people to download his skewed testing sequences from his website in order to prove that they, too, have the same ability! Sure enough, that seems to be what they really do find, and you can too - unless, perhaps, you flip a coin instead!
` Naturally, a very real feeling of 'being watched' does exist, even when you don't see the watcher. If I had to guess, part of this probably has to do with the fact that for thousands of years, human beings have been both predators and prey - even towards each other. And, as with my own 'dad-alert' ability, it probably has to do with hearing, because an animal suddenly tries to be stealthy when it becomes aware of a human.
` But is the animal being stealthy in order to hide, or stealthy in order to strike? Either way, sensing this is to your advantage!
` It's a reasonable hypothesis, sure. But to explain the feeling of being watched also as a psychic ability? Even cases where it seems to be true are, well, not what they seem.
` Such revelations are the consequences of having a curious and open mind. After all, you never know what you're going to discover. Especially back when there seemed to be inexhaustable amounts of discovering being done all the time!
` When British explorer Harry Johnston set out into the jungles of the Congo to find a striped animal once nicknamed the 'African unicorn', he suspected it was some type of zebra.
` As governor of Uganda, he rescued some Wambutti pygmies from a German showman, who intended to display them in Europe. On the way back to their jungle home, the grateful pygmies told Johnston about the animal he sought, and even showed him its hoof-prints!
` But these were not zebra tracks; they were cloven! So, Johnston changed his mind about what was going on, and instead suspected it was a type of eland. But when the pygmies were able to show him some remains, he found that it was neither zebra nor antelope; it was closely related to giraffes!
` In his honor, this sacred animal of the pygmies, which they called o'api, was scientifically named Okapia johnstoni.
` I guess one could say; sacred cows (or zebras) aren't allowed if they are sacred okapis. Oh, stop groaning!
` Unfortunately, while people are not usually afraid of finding new species, astronomical objects, or genes, they often are afraid to discover new ways that they have been deceived. They don't want their preconceptions to be dashed.
` Is it any surprise that these people are the ones who have told me that I am too ignorant to understand that the scientific method and the logic that goes with it (generally referred to as modern skepticism) is not a problem-solving tool at all? Science has very little to offer, they say, because it is just another dogmatic religion.
` Dogmatic religion? Ultimately bowing down to reality, rather than someone's rigid, preconceived framework, is what science is all about! But no, they say, I am the one who has been deceived; I am the know-it-all whose faith in science is so blind that I cannot see how narrow my mind has been made!
` To be fair, I used to take this view myself saying the same harsh words towards scientists and skeptics. How dare they say that psychic powers are an illusion? I had them! Or ghosts? I'd seen one! Or alien abductions? Well, about the alien abductions; by the time I'd had my second one I was fairly certain they were illusions.
` Though being paralyzed and floating through my window into the mothership seemed real enough, I managed to take control, turning the aliens purple! I started laughing, and then I noticed that I was 'suddenly' still in bed!
` Those experiences, by the way, were my second and third episodes of sleep paralysis - and I've had others of various different types since then. (I will certainly have to write about these some time!)
` It is for the people who think they cannot be fooled that I once wrote a little story:
` Grig and Danald are two stone-age pioneers, still discovering a strange new continent. They are among the first people ever to set foot in this place, and are trying to determine the identity of a mysterious scavenger.
` It seems that every time they carry off the first load of a Pleistocene-sized kill to their tiny settlement, the carcass has been completely stripped by the time they get back!
` They know that the carnivorous marsupials they have encountered could not be the culprits, as the tracks left around the carcass are not paw-prints: Instead, they look like they were left by the dragging gait of a large reptile.
` One day, Grig and Danald brought down quite a large wombat-like animal (Diprotodon to you and me), and have smoked and packed up much of the meat. It is then that the topic of the mysterious scavenger came up.
` Grig volunteered a hypothesis; "You know, I think that those tracks were left by some sort of crocodile."
` "But we're not even near any large-enough watering hole," said Danald. "Don't crocodiles usually stay around water almost all the time?"
` "That's true," said Grig. "But these tracks are very similar - you can even see the tail! Maybe it's just a different kind of crocodile." He looked around nervously and picked up his pack. "In that case, we'd better leave!"
` "Well, you know what I think, Grig?" Danald said, picking up his own pack. "The reason we never see this thing is because it's not a living animal at all; it's the wandering spirit of a lonely and hungry crocodile that was shunned by its brothers and sisters. That's why it doesn't have to be around water."
` "That doesn't make much sense," said Grig. "Everyone knows that spirit crocodiles can't leave tracks, nor do they drag unsuspecting animals under the water to eat them. They live in a whole different world we can't usually see! I say, it's a big animal with sharp teeth, whatever it is!"
` "Maybe spirit crocodiles can't hunt animals," said Danald, "but what if they can eat something that's already been killed?"
` "Danald," Grig sighed, "to say the least, I think a council with the shaman is in order."
` "Good! Then maybe he will prove me right!"
` Hearing a noise behind him, Grig turned to see that they were being monitored by dark eyes and a long, flicking tongue.
` Alas, both of the hunters' hypotheses had just been dashed to bits upon their discovery of the half-ton monitor lizard, Megalania prisca.
` "What the..." Danald gasped and looked around for Grig.
` But he was already running for his life.
` Award-winning it's not, but the moral is; without objectivity, you could wind up getting bit on the... well, in this case, possibly several areas at once!
34 comments:
S. E. E. Quine:
"In that way, our intuition can lead us into believing in the strangest and most wonderful ideas, even when they aren't true."
"Strange and wonderful" yes, but it carries the baggage of bias. Thus, the virtues of a strong discipline of the "scientific method".
I certainly wasn't expecting that a cat would find a giraffe mask, or bring it home. Strange cat.
` Yes, Mercury, bias isn't the greatest thing on the planet. This is why I say; open-mindedness plus disciplinedness sometimes equal killjoyedness!
` Well, Charles, at least the cat only brings in inanimate objects - his brother brings in fully animate objects!
That was a whole lotta writing! It could be shorter, but it was good enough that I deduced your main message was:
"Being open-minded when you want to isn't hard, but if you want to be objective, you also have to be open-minded when you don't want to."
P.S., I don't know why, but I thought Grig and Danald were hilarious!
` I couldn't have said it better myself, Galtron! In fact, I may quote you in a future post....
S. E. E. Quine:
Any parallels between Kluge ("Clever") Hans and Oscar the "harbinger of death"?
Nevertheless, this pursuit of knowledge and "truth" about the universe is predicated upon the validity of our ability to accurately gather data and extrapolate the information into universal laws of physics. There are some problems here in the assumption that the instruments are giving the correct information--the infallible data--and that we are making the correct interpretation. It may be somewhat arrogant--given the vastness of the universe--that what we discover as the immutable laws of the universe are entirely inapplicable one million light years away; that the physical laws for those citizens would be slightly off or totally inverted. This form of epistemology--the total universal knowledge--may never be known do to issues in gathering all the data and that mankind may simply be incapable of comprehension of such a volume of information. Consider another life form not based on carbon but rather boron or even silicon--hard for humans to comprehend based on what we have discovered about what it take for life.
"that what we discover as the immutable laws of the universe are entirely inapplicable one million light years away; that the physical laws for those citizens would be slightly off or totally inverted."
We really have no reason to believe that there may be differing physical laws, as there has been no observed phenomenon to suggest otherwise. So far all man has seen can be explained within what we hold to be the most reasonable explanations we have before us.
` Yes, Mercury, I did notice the similarity between Oscar and Hans, which is why I almost worked it into this post. However, I decided it was long enough.
` But yes, I think there could be lots of different interpretations for the cat's ability to 'predict' impending death, such has his interpretation of a dying person's sounds as 'purring'.
` Whatever it is, it may be another one of those 'Clever Hans' illusions in which people think one thing is going on when it is another. But really, nobody knows what it is in the first place.
` In fact, there may actually be no correlation to the cat curling up to someone and their dying at all, though that remains to be determined.
` And as far as the 'laws of nature' go, I don't know why anyone would think they were different in other sections of the universe. (Like Charles said.) If they were, you'd think either that we would notice, or that there would be some sort of disturbance between boundaries or something.
` I've always wondered what silicon-based life would be like. Transparent, perhaps?
S. E. E. Quine:
Silicon based would be more "rock like". Recall the original "Star Trek" series. One of the most humorous episodes involved a species that was thwarting an important mining operation. The creatures burrowed under the planet's surface and was, I believe, called a "Hora". The main alien was a female of the species acting in self-defense of her young hatching brood. During several encounters, the Hora was wounded and through the intervention of Mr. Spock's "mind meld" discovered the benign nature of the creature. Dr. McCoy was beamed down to put his medical powers to use only to discover that the biometrics of the creature were totally different--silicon based. Exclaiming that he was a physician and not a mason, he nevertheless ordered some cement and a trowel from the ship's store room to repair the alien. Needless to say, everything worked out fine for an agreement between the mining company and the alien species was arranged: Self preservation for the exchange of many aliens burrowing new tunnels for the precious mineral.
S. E. E. Quine/Charles:
Well, you may disagree if you like, but that is a very closed epistemology. It is a "fallacy of composition"...saying that just because something is true here that it is true universally. The universe is very large and no doubt full of unexplained things yet to be discovered. It would appear odd that all phenomena is displayed or observed from earth's perspective. It is man's arrogance to assume what we observe and codify is "true" everywhere...where is it stipulated that Earth observations are to be employed throughout the universe. Universal diversity is not necessarily defined by earthly concepts. That would be a closed system of analysis.
Furthermore:
"We really have no reason to believe that there may be differing physical laws, as there has been no observed phenomenon to suggest otherwise."
This is a classic example of "argumentum ad ignorantiam": There is no evidence for "x"; therefore, not "x"...or...there is no evidence against "x"; therefore, "x". Not knowing beyond our sphere of epistemology does not guarantee what we know as being universal.
` Mercury! Thank chickens my internet is finally up and running again!
` Ah, so that's what the rock alien was supposed to be! In that case, visiting astronauts might not even know silicon-based life when they see it! Now that would be nuts!
` It's not that I don't think it's outright impossible, but the idea of our universe being broken into different regions with different laws is purely speculative.
S. E. E. Quine:
"It's not that I don't think it's outright impossible, but the idea of our universe being broken into different regions with different laws is purely speculative."
The set of physical laws we observe may just be a subset [a corollary] to a much larger set that is yet to be discovered. This conjecture certainly lies in the realm of philosophy and metaphysics. The answer may never be known or simply beyond the comprehension of mankind...thus the value of metaphysics.
S. E. E. Quine:
I don't want to stray too far from your theme, but it is curious to note and speculate on the uniqueness of the carbon atom being associated with life. Silicon may well be out of the realm of reality [mating with rocks would be difficult] but carbon's neighbor "boron" would be the next most likely candidate.
Gaze at the periodic table and look at all the elements and speculate why "carbon" is the basis for life as we experience it. What are the criteria for life to form? You look at the chart and wonder why carbon instead boron [ or even silicon and sulphur]. Boron is the nearest choice but boron has problems of its own. But why just carbon? Several come to mind: The ability to have free electrons that can produce a variety of chemical bonds, the ability to replicate with DNA/RNA, and its abundance. It is quite unique that carbon has a fine chemical relationship with hydrogen, oxygen, nitrogen, phosphorus, calcium, and sulfur. The replication feature is characteristic of DNA/RNA molecules called "Linear Polymeric Molecules" and it is these molecules that are composed of simple to complex combinations of hydrogen, oxygen, nitrogen, phosphorus, calcium, and sulfur. [To note: Trace elements are also employed such as zinc, molybdenum, selenium and the biggies like sodium, potassium, and iron.] Carbon's nearest neighbor, boron, can to some degree display similar molecules but is a bit erratic in that the number of chemical bonds varies from three to six [the same for silicon and sulphur]--not predictable enough to perform replication whereas carbon bonding is always four and very reproducible. And lastly, boron for example is just not that abundant. It looks like that the chemical characteristics fill the criteria for the evolution of life.
S. E. E. Quine:
At least you will contemplate and allow some validity to what I said...
"` In science, of course, surprises are to be expected and any personal preconceptions are to be criticized if they don't seem to match reality. As they say, there are no 'sacred cows' allowed!
` This is what allows scientific hypotheses (and occasionally full-blown theories) to change as more information is discovered. Mistakes, therefore, can be corrected. After all, part of a scientist's training is learning that they don't know THE truth - they only know what is likely to be the truth, with the information they have at the time."
One often wonders what will happen, if at all possible, when everything is known about the universe--then what? Do we vegetate...turn into pure energy?
` Mercury said:
The set of physical laws we observe may just be a subset [a corollary] to a much larger set that is yet to be discovered.
` That does seem probable, when you put it that way. What do we know?
` I personally find such speculations overwhelming unless some way to uncover them is possible.
` There may be, someday!
It looks like that the chemical characteristics fill the criteria for the evolution of life.
` Of carbon? Indeed - I guess we're just lucky that way!
One often wonders what will happen, if at all possible, when everything is known about the universe--then what? Do we vegetate...turn into pure energy?
` Probably nothing. ...Unless the universe is some kind of a puzzle and the embedded life forms are supposed to figure it out.
` In that case, we might get a really big cookie for our efforts!
S. E. E. Quine:
"Luck" has nothing to do with carbon being the basic of a life form [as I indicated above]...it is physics and subsciences of chemistry, biology, etc.
The desire of knowing "all" the physics of the universe is a sought after pipe dream of dire consequences and ultimately the loss of "uniqueness" and "freewill". Physicists, especially those dreamy theoretical physicists that can't seam to separate fact from fiction; that would rather find comfort in science fiction; that have lost the fundamental concepts of the scientific methodology are the ones that wish for a TOE ["Theory Of Everything"]. That is a far cry from a more sound epistemology of a GUT ["Grand Unified Theory"] where empirical evidence allows a source of knowledge and yet recognizes that there are going to be things we will never know and maybe shouldn't know. The GUT will allow "uniqueness" and "freewill". Now I have a colleague that would argue in defense of a TOE; that all human actions can be described by neuron activity--including "uniqueness" and "freewill". Unfortunately for him, he will not receive that "really big cookie".
` You know, I think it's actually comforting that we will probably never know everything. I like a good mystery.
` I probably ought to clarify; I meant that we're lucky to have carbon to make us!
S. E. E. Quine:
"Mystery" or rather scientifically: That which can not be explained by empirical evidence falls into a legitimate form of epistemology..."metaphysics". Examples: An edge to the universe, quantified physics of the quantum realm, events prior to the "big bang", God.
Expand...why are we "...lucky to have carbon to make us!"
'Silicon based would be more "rock like".'
Consider that both Silly Putty and Neoprene are both silicon based, neither of them are 'rock like.'
Charles:
You said "...both Silly Putty and Neoprene are both silicon based...." Not quite accurate. Polydimethylsiloxane is a complex polymer silicone base [Silly Putty]. That one is correct. But neoprene [duprene] is not silicone based--not a single atom of silicone is present in it's basic manufacture. Neoprene is nothing more than the polymerization of chloroprene [2-chloro-1,3-butadiene]. No silicone there. Furthermore these products are synthesized via complex organic chemistry methods of polymerization. The point I assumed that would be understood was that naturally occurring rocks and minerals consisting of many silicone inorganic and organic compounds that could possibly function as a carbon atom and exhibit those characteristics common for the formation of simple to complex molecules for the formation of life. But our chemistry does not allow the multiplicity exhibited by the carbon atom to assume similar characteristics in the silicon atom or even the boron atom.
Ok, I boo-booed, the "silicon rubber" wasn't neoprene. I'm not saying that life based on silicon is possible, just that just because silicon is in the compound, it doesn't mean that it would be rock solid. But we do have "silicon rubber," I just don't remember which it is. I think if some other element were to form the basis of life, it might be something like phosphorus, arsenic, antimony or even nitrogen. I'm not a chemist by any means, so please forgive my faux pas.
Charles:
An old carpenter's axiom..."measure twice, cut once."
[Incidentally, "silicone rubber" is not a specific product like neoprene or similar isomers but a huge categorical classification of many compounds with various characteristics and uses.]
Again my point is missed, for the chemistry [affinity for bonding in unique methodologies] is apparent only for what we can recognize as a life form base and that is carbon--not any adjacent elements or even the remote ones you mentioned ["...phosphorus, arsenic, antimony...."]. Given the vastness of the universe and our limited understanding, it would be illogical to assume universal laws; that a simple physics formula [Newton] f=ma [force=mass times acceleration] may be seen to be something else as in f=m^2a [force=mass squared times acceleration]. All of these postulates we derive within our sphere of observation and analysis are serious epistemological issues of which may never be answered. And to "a priori" dismiss alternate perspectives is just poor philosophy. The ice cream vendor at infinity may be a sentient being of robot appearance whose conscience is comprised mostly of boron. Who knows.
But we have digressed from the theme of this essay.
` All I mean by us being lucky to have carbon around to make us is that; it's nice that something so versatile exists!
` For carbon-based life forms, this means we have a lot of possibilities going for us. (At least in this section of the universe!)
S. E. E. Quine:
"For carbon-based life forms, this means we have a lot of possibilities going for us." I cannot argue against that realizing the vast potential of stem cell research and the far reaches of organic chemistry. We can stop and prevent diseases of the human body, extend the life span, increase mental capacity and in the long run stabilize societies to a maturation never dreamed of before.
S. E. E. Quine:
In a round about way you have admitted to what I have been arguing: "After all, part of a scientist's training is learning that that they don't know THE truth - they only know what is likely to be the truth, with the information they have at the time." Absolute knowledge is illusive and what we now know is good and heuristic but will be challenged. Hegel's dialectic in action?
Ok, I'll give you that what we perceive as knowledge, could very well be entirely different than the actual truth. Quantum physics points out that our "laws" aren't all inclusive. But that is a matter of scale and the macro scale "laws" that we observe still apply on the macro scale or non-quantum scale. True that there may be other laws applying elsewhere, but the question would be "where?" I've heard the theories of "other universes," but I have to ask the question, how can there be other universes, when by definition of universe is everything that exists anywhere?
Charles:
The activities that occur within the realm of the quantum world are, as of now, unquantifiable; they defy specific analysis and predictability; Newtonian Mechanics [your "macro-scale" physics] fail to describe events but function good in the world of the large. This may just be the way things will be and we will have to interpret such events on statistical physics. The physics involved may simply be beyond our comprehension of analysis and even beyond our means of physical analysis [the instruments used to observe and measure the quantum events.] Thus, a shaky epistemology [from an empirical perspective] will lie solely in the realm of the nebulous arena of theoretical physics and probably permanently reside within the scope of philosophy--specifically metaphysics. Not a bad thing, for "mystery" [the unexplained] has a perfectly legitimate place in our perspective and interpretation of the universe. As I indicated before a TOE necessitates a sea of philosophical issues. For example: The quantification of God has always failed. Empirical evidence is just not there. But many wish for a physical entity and it "is" equally comforting to find solace in "just" the concept of God separate from corporeality...value is not always associated with the tangible. This is metaphysics...the same for a TOE or ultimate understanding of the quantum realm--not needed, not knowable. If all were known, a lot of physicists [scientists] would be unemployed...relegated to making better mousetraps.
"...there may be other laws applying elsewhere, but the question would be "where?""
Again, unknown and may never be known. After all, the universe as we observe is expanding rapidly [red shift phenomena] and all attempts to decipher the physics would be thwarted. A deterministic perspective for sure in the realm of epistemology and a further extension in realizing that mankind becomes more and more isolated from the possibility of exchanging experiences and knowledge with other sentient beings...space travel from point "A" to point "B" takes longer with added risks.
"...how can there be other universes, when by definition of universe is everything that exists anywhere?"
I simply don't understand that statement.
Charles:
Maybe of interest to you.
[I post the whole article for links do disappear to other areas of cyber space in time.]
"ScientificAmerican"
July 15, 2007
"The Gedanken Experimenter"
In putting teleportation, entanglement and other quantum oddities to the test, physicist Anton Zeilinger hopes to find out just how unreal quantum reality can get.
by J. R. Minkel
Physicist Anton Zeilinger may not understand quantum mechanics, but he has not let that stand in his path. Besides paving the way for ultrapowerful computers and unbreakable codes that run on quantum effects, the 62-year-old Austrian has a gift for pushing the limits of quantum strangeness in striking ways. Recently he observed the delicate quantum link of entanglement in light flickered between two of the Canary Islands, 144 kilometers apart. He dreams of bouncing entangled light off of satellites in orbit.
Though better known to the world at large for such headline-grabbing experiments, Zeilinger, who is based at the University of Vienna, has gone to comparable lengths to test the underlying assumptions of quantum mechanics itself. His results have left little hiding space from the conclusion that quantum reality is utterly, inescapably odd—so much so that 40 years after first encountering it as a student, Zeilinger still gropes for what makes it tick. "I made what I think was the right conclusion right away," he says, "that nobody really understands it."
For almost 17 years Zeilinger's work has centered on tricks of entangled light. Two particles are called entangled if they share the same fuzzy quantum state, meaning neither of them begins with definite properties such as location or polarization (which can be thought of as a particle's spatial orientation). Measure the polarization of one photon, and it randomly adopts a certain value, say, horizontal or vertical. Oddly, the polarization of the other photon will always match that of its partner. Zeilinger, whose group invented a common tool for entangling polarization, likes to illustrate the idea by imagining a pair of dice that always land on matching numbers.
Equally mysterious, the act of measuring one photon's polarization immediately forces the second photon to adopt a complementary value. This change happens instantaneously, even if the photons are across the galaxy. The light-speed limit obeyed by the rest of the world can take a leap, for all that quantum physics cares.
Scientists have come to view entanglement as a tool for manipulating information. A web of entangled photons might enable investigators to run powerful quantum algorithms capable of breaking today's most secure coded messages or simulating molecules for drug and materials design. For six years Zeilinger pushed the record for most number of photons entangled—three, then four (bumped to five in 2004, then six, by a former researcher in his group). In 1997 Zeilinger first demonstrated quantum teleportation: he entangled a photon with a member of a second entangled pair, causing the first photon to imprint its quantum state onto the other member. Teleportation could keep signals fresh in quantum computers [see "Quantum Teleportation," by Anton Zeilinger; Scientific American, April 2000].
A few years later his group was one of three to encode secret messages in strings of entangled photons, which eavesdroppers could not intercept without garbling the message. He is not always the first to achieve such a feat, but "he has a very good eye for an elegant experiment and one that will convey the thing that he's trying to convey," says quantum optics researcher Paul G. Kwiat of the University of Illinois, a former member of Zeilinger's lab who is now a collaborator.
"The only reason I do physics is because I like fundamental questions," Zeilinger says between bites of bagel with cream cheese and honey. He had come to Denver for a physics meeting, where he would tell assembled colleagues of his work beaming entangled photons between La Palma and Tenerife in the Canary Islands—extending the range of secret entangled messages by 10-fold.
Broad-faced and smiling, with oval glasses scrunched between his beard and a puff of frizzy gray hair, he looks a little wolflike—ready to catch quantum prey. "All I do is for the fun," he says.
Part of his fun is confirming the strangeness of quantum mechanics. Quantum indeterminacy notoriously bothered Albert Einstein, who called the theory incomplete. A particle should know where and what it is, he believed, even if we do not, and it should certainly not receive signals more quickly than at light speed.
Einstein's view remained a matter of interpretation and in the realm of gedanken, or thought, experiments until 1964, when Irish physicist John Bell proved that measurements of entangled particles could distinguish quantum mechanics from Einstein's position, a mix of locality (signals flow at light speed) and realism (particles possess definite, albeit hidden, properties).
Light-based tests of Bell's theorem require two detectors to rapidly switch the directions along which they measure the polarizations of entangled pairs. Statistically, local realism dictates that the polarizations can be linked, or correlated, only for a certain percentage of measurements. In a classic 1982 Bell test that set the standard for future attempts, French physicists upheld quantum mechanics—and upended local realism—by observing a greater percentage.
Zeilinger's first foray into entanglement was as a theorist, when, in 1989, he co-invented a nonstatistical version of Bell's theorem for three entangled particles—called GHZ states, after the last names of the discoverers (Daniel M. Greenberger of the City College of New York, Michael A. Horne of Stonehill College in Easton, Mass., and Zeilinger). The trio imagined three entangled photons each striking a detector set to measure polarization in one of two directions, either horizontal-vertical or twisted left or right. In principle, four combinations of detector settings would set up a single measurement capable of distinguishing quantum mechanics from local realism.
"It was the biggest advance in the whole business of the comparison of quantum mechanics to local realistic theories since Bell's original work," says physicist Anthony J. Leggett of the University of Illinois. Realizing the GHZ experiment took Zeilinger until 2000.
The year before, he also closed a loophole in the 1982 French experiment (other loopholes remain) by using two briskly ticking atomic clocks to preclude any chance that the detectors were somehow comparing notes sent at light speed.
A few months ago Zeilinger reported implementing a new kind of statistical Bell test, devised by Leggett, that pits quantum mechanics against a category of theories in which entangled photons have real polarizations but exchange hidden particles that travel faster than light. In principle, such faster-than-light theories might have perfectly mimicked quantum strangeness and let realism go unmolested. Not so, according to the experiment: the results could be explained only by quantum unreality.
So what idea replaces realism? The situation calls to mind one of Zeilinger's favorite books, the humorous novel The Hitchhiker's Guide to the Galaxy, by Douglas Adams, in which a mighty computer crunches the meaning of life, the universe and everything and spits out the number 42. So its creators build a bigger computer to discover the question. (An avid sailor, Zeilinger named his boat 42.)
If quantum indeterminacy is like the number 42, then what idea makes it intelligible? Zeilinger's guess is information. Just like a bit can be 0 or 1, a measured particle ends up either here or there. But if a particle carries only that one bit of information, it will have none left over to specify its location before the measurement.
Unlike Einstein, Zeilinger accepts that randomness is reality's bedrock. Still, "I can't believe that quantum mechanics is the final word," he says. "I have a feeling that if we get really deep insight into why the world has quantum mechanics"—where the 42 comes from—"we might go beyond. That's what I hope." Then, finally, would come understanding.
© 1996-2007 Scientific American, Inc.
S. E. E. Quine and Charles:
On a much broader scale one could believe in what Sir Arthur Edington said ""Not only is the universe stranger than we imagine, it is stranger than we can imagine." Or, and I didn't say this,: "What is about us that makes us capable of supposing anything, thinking and comprehending things? And does this tells us anything about what we can suppose? Are there things about the universe that will be forever beyond our grasps but not beyond the grasps of some superior intelligence? Are there things about the universe that are forever un-graspable by any mind, however superior?" That incidentally was written by Richard Dawkins. The point is simple...some knowledge of the universe may be denied.
` I suppose, then, that the limitations of the human brain may be the ultimate security code for keeping us out of these things.
` In that case, I wonder what would happen if we ever adapted to some crazy life such as traveling through wormholes or something on a regular basis?
` Could our brains gradually evolve to answer larger and larger questions?
Others share a view of limitations:
From: seedmagazine.com
Physics & Math
"Seeing the Unseeable"
The limits of our senses confront the limitlessness of the universe.
by Maggie Wittlin
Within the confines of the ordinary, vision is the most reliable tool we have. But some of the most extraordinary parts of nature, those that lie at the frontiers of science, can't be seen at all. Dark matter, for example, the invisible, mysterious material that makes up 22 percent of the stuff in the universe, is one of the great scientific unknowns, a substance nearly six times as abundant as ordinary matter but made up of fundamental particles we haven't yet identified. And dark matter doesn't emit light, it doesn't reflect light, and it doesn't absorb light. It's not dark, as the name suggests—dark matter is completely, inherently unseeable.
While we are unable to see dark matter itself, we are able to create maps of it, pinpointing
its location by observing the effects of its mass on light from distant galaxies. Einstein's general theory of relativity predicts that a massive object will curve the fabric of space, and light will follow this deformed path. So we can look at how light from galaxies has been bent and infer the quantity and location of the matter that did the bending. An international team of astronomers recently used this method to create the first three-dimensional map of the large-scale structure of dark matter, and they released this blue and black image earlier this year.
In one sense, the image is categorically sublime. Scientists have taken something that cannot be seen, and they've let us see it. They've not only increased our knowledge of the large-scale structure of dark matter, they've also taken something inherently invisible and given it an accessible beauty. While we used to struggle to conceive of dark matter, using phrases like "pervasive stuff" and "ineffable material" to force it into the confines of language, we can now imagine it as a grand network with dense hubs and small offshoot islands.
But when we start to intuit dark matter rather than discuss it rigorously, we are in danger of imagining it as too much like ordinary matter. In fact, dark matter's invisibility tells us that it has another remarkable attribute: Unlike normal matter, dark matter is not made up of charged particles. Maxwell's equations, the four expressions at the heart of electromagnetism, tell us that moving charges can create electromagnetic radiation; they tell us that charge produces light. So because dark matter does not interact in any way with electromagnetic radiation, we can conclude that it is uncharged. This, in turn, implies that dark matter is nearly collisionless—individual particles don't bounce off of one another or off of ordinary matter; almost all of them just pass through as if nothing were there. We are constantly being irradiated by the billions of dark matter particles that pass through our bodies every second, but these particles will never touch our flesh or our organs. Were we able to see dark matter, we would be justified in assuming we could interact with it. So when we look at an image and perceive dark matter as a seeable substance, we implicitly imbue it with a property it doesn't have.
As people, we take in pictures with ease—absorbing visual information is, after all, our evolutionary specialty—but in any scientific case in which we see the unseeable, we sacrifice a little bit of understanding. To crib from Tolstoy, "All seeable things are alike; each unseeable thing is unseeable in its own way." Visible objects are all composed of atoms that emit light within a certain frequency range; they're all macroscopic; and they all exist in our three spatial dimensions. When scientists discover something invisible, the cause of its unseeability will inevitably be tied with what makes it exciting.
That an object is too small to be seen by the naked eye doesn't tell us much about it, but when an object is so small that it cannot be precisely observed even in theory—when an object enters the realm of quantum mechanics—its unseeability is at the center of its nature. An object that is so small it obeys the laws of quantum mechanics (an electron in an atom, for example) can exist in many locations at one instant in time. But when we measure the location of the electron, when we look at it, it collapses into one spot. We cannot observe it in its natural state, and any image of an atom, from the oversimplified but popular solar system model to a computer-generated graphic of foggy orbitals, will be unable to fully capture this amazing idea that by seeing the electron, we change it. General relativity demands that space itself curves in response to mass. We allow ourselves to picture a ball sitting on a rubber sheet, deforming it with a depression, but in reality, this deformation doesn't happen in one preferred direction; it happens uniformly in all directions, and this is impossible to construct in our mind's eye.
When science presents us with an image of dark matter, of electron orbitals, of general relativity, of anything fundamentally unseeable, it teases us. The visual draws us in with its incredible elegance; it lets us think for just a moment that the secrets of the universe are spread out before our eyes. And then, as we start to read the text that inevitably accompanies the picture, it hits us: Our eyes will never be as big as our science. Our visual system is the best source of intuitive information, the kind of stuff that we need to survive, but it gives us only a shadow of the greater world.
To see the unseeable is glorious and awe-inspiring, it's disquieting and misleading, it makes us question our ability to understand the world and allows us to marvel at our ability to learn so much despite our limitations. And, in some way, it's what we've been doing all along. Scientists and other curious people have always needed to turn unseeable phenomena into visuals. Experimentation is the art of prodding some invisible aspect of nature and turning its response into something we can see. Whether we watch two balls dropped from a tower hit the ground at the same time or observe flashes of light as an alpha particle is scattered off of a gold nucleus onto a screen, we bring the world to us, giving ourselves a simple image that lets us learn about a universe that doesn't care whether or not we can understand it.
` I admit, it seems I've forgotten most of what I've learned about physics.
` Neither does my boyfriend, it looks like, so our debates within the subject matter are atrocious.
` This article reminds me of the time he said that he thought dark matter was a stupid idea because; why couldn't it be regular matter that's merely dark that's affecting gravity?
` I told him that dark matter is actually transparent, so you can only see its gravity-warping effect on light, as well as its ability to pull galaxies together a lot more than would be otherwise expected.
` There's so much of it that if dark matter were actually regular matter out in space that simply didn't emit any light, we wouldn't be able to see the stars!
` Then he said he thought that the physicists' calculations must therefore be way off.
` But I didn't know what to say to that. The article, however, at least informs me that 1) if they're wrong, they're six orders of magnitude wrong, and 2) the reason dark matter doesn't interact with anything is because it doesn't have a charge.
` Well that makes tons of sense! Charge, as far as I know, determines how particles interact with other particles.
` Is there anything else really essential I should know about dark matter?
` And also, I've wondered; what about dark energy? How well does that hold up against scrutiny?
` Don't tell me - it's all on Worthy Science Sources!
` Well, no time for that at the moment, but I'll be back....
` Hmmm. I did't see anything about dark matter or anything on WSS... but I did learn a little more about it.
` I was using my newfound knowledge to have a slightly less ignorant conversation with my boyfriend.
` His conclusion?
` "I think they're on drugs."
` I tried....
I am no expert on "dark matter" but here is an article by Martin White.
Dark Matter
Nearly 50 years ago, Fritz Zwicky realized that clusters of galaxies consisted predominantly of matter in some nonluminous form. The search for dark matter has dominated cosmology for half a century. Precise measurements were obtained over 20 years ago, when dark matter was first mapped in galaxy halos. Only recently has the existence of dark matter over much larger scales than even galaxy clusters been confirmed.
The density of matter in the solar neighborhood is measured by sampling a uniform population of luminous stars that extends well above the disk of the galaxy. The average velocities of the stars and the vertical distances they traverse above the disk provide a measure of the gravitational restoring force that keeps these stars in the disk. From the strength of this force, one can deduce the total density of matter that exerts this gravitational pull. Comparing this density with actual counts of stars, one finds that the number of observed stars falls short, by perhaps as much as a factor of 2, of the number needed to account for this density. This is the first hint of any dark matter, and it is present in the vicinity of the sun. It should be noted that the amount of such a shortfall in the disk matter is controversial.
There is at most an amount of dark matter in the disk equal to the amount of luminous matter. A more conservative estimate might place the amount of dark matter at about 25 percent of the amount of luminous matter. In fact, this additional component of matter need be nothing very exotic.
What could the dark matter be? The dark matter in the disk most likely consists of very dim stars, such as white and even black dwarfs. White dwarfs are the destiny of stars like the sun, attained when the nuclear fuel supply is exhausted. A typical white dwarf has a mass of about 0.6 the mass of the sun but a size smaller than that of the earth. It formed as the hot core of a planetary nebula, the final luminous phase of stellar evolution when the envelope of a red giant is ejected as the core burns the last remnants of nuclear fuel. A white dwarf fades slowly to oblivion as it cools down to become a black dwarf.
A useful measure of mass is obtained by taking the ratio of the mass of all stars to the to the luminosity emitted by all stars, in a volume of a few hundred parsecs around the sun. If the typical star near the sun was equal in mass to the sun, the ratio of total mass to total light would be unity, larger than unity if the typical star was less massive, and smaller than unity for more massive stars. Since the resulting ratio is found to be 2 for nearby stars, in solar units of solar mass (M) to solar luminosity (L): M/L we conclude that the average star near the sun is slightly less massive than the sun. In the solar vicinity, there is little necessity for any dark matter other than the dark dwarfs. The first real surprise emerges in the outermost parts of galaxies, known as galaxy halos. Here, there is negligible luminosity, yet there are occasional orbiting gas clouds, both atomic and ionized, which allow one to measure rotation velocities and distances. The rotation velocity is found not to decrease with increasing distance from the galactic center. This constancy of velocity implies that the galaxy's cumulative mass must continue to increase with the radial distance from the center of the galaxy, even though the cumulative amount of light levels off.
Just how much additional mass is in the halo? This rise appears to stop at about 50 kiloparsecs, where the halo seems to be truncated. We infer that the mass--to--luminosity ratio of the galaxy, including its disk halo, is about five times larger than estimated for the luminous inner region, or equal to about 50. This is the first solid, incontrovertible evidence for dark matter. The rotation velocities throughout many spiral galaxies have been measured, and all reveal dominance by dark matter.
Moving further afield, the mass-to-light ratio can also be evaluated by studying galaxy pairs, groups, and clusters. In each case, one measures velocities and length scales, from which one determines of the total mass required to provide the necessary self-gravity to stop the system from flying apart. The inferred ratio of mass to luminosity is about 100M/L for galaxy pairs, which typically have separations of about 100 kiloparsecs. The mass-to-luminosity ratio increases to 300 for groups and clusters of galaxies over a length scale of about 1 megaparsec. Over this scale, 95 percent of the measured mass is dark.
The largest scale on which the mass density has been measured with any precision is that of superclusters. A supercluster is an aggregate of several clusters of galaxies, extending over about 10 megaparsecs. Our local supercluster is an extended distribution of galaxies centered on the Virgo cluster, some 10 to 20 megaparsecs distant. The mass between us and Virgo tends to decelerate the recession of our galaxy relative to Virgo, as expected according to Hubble's law, by about 10 percent. This deviation from the uniform Hubble expansion can be mapped out for the galaxies throughout this region, and provides a measure of the mean density within the Virgo supercluster. Over the extent of our local supercluster, about 20 megaparsecs, one again finds a ratio of mass to luminosity equal to approximately 300.
On the very largest scales, there are no longer any gravitationally bound objects. Yet the galaxies are not distributed perfectly uniformly: there remain small density fluctuations that have persisted since the very earliest epochs of the universe. The dark matter that accounts for the critical density should, at least in the case of some kinds of dark matter, participate in the density fluctuations on large scales. If one measures the `peculiar' velocities of galaxies relative to the Hubble flow, they will trace trace the fluctuating component of the dark matter. The resulting maps reveal large-scale bulk flows that amount to about 10 percent of the Hubble expansion and are coherent over 30 megaparsecs or more. The flows are induced by the gravitational attraction from all matter present, and therefore probe the total amount of clumped matter, dark as well as light. Preliminary indications are that an amount of dark matter about equal to the critical density must be present in order to account for the amplitude of the observed flows. One can even pinpoint the sources of the flows, since there are vast concentrations of matter that must be responsible. The nearest one has been dubbed the Great Attractor; it is located at a distance of 40 megaparsecs from us. If real, it must consist of more galaxies than would be found in a dozen rich galaxy clusters. Our galactic plane obscures a large part of the Great Attractor, so one cannot count the number of galaxies directly. There may well be other similar complexes of galaxies that help generate the bulk flows.
The theory of inflation predicts that we live in a flat universe, where the density parameter Omega is equal to unity. That is, the density of matter in the universe should just equal the critical density at which the universe is closed. Can we tell from the amount of dark matter observed whether the universe is indeed at critical density, as the theory of inflation predicts? One can translate the Omega parameter, which measures mass density in terms of the critical value into a ratio of mass to light. One does this by taking the ratio of the critical density to the observed luminosity density of an average, and large, volume of the universe. The result is that the mass-to-light ratio equals 1500 Omega. In other words, if Omega is 1, one needs a mass-to-light ratio of 1500 to close the universe. This amount of mass is far greater than is observed directly. Alternatively, if we adopt the mass-to-light ratio of 300 measured on large scales as being a universal value, we would conclude that Omega is 0.2, far less than the value predicted by inflation. One can reconcile inflation theory with observation only if the bulk of the dark matter is uniformly distributed over scales up to 10 megaparsecs. In this case, the dark matter would not have shown up, since on these scales only the clumped component of the matter has been measured. Indeed, a critical density would be compatible with the density measured by the bulk flows, which only sample scales larger than 10 megaparsecs or so.
The nature of the dark matter predicted by inflation is a profound and unresolved puzzle. We have two choices. Either the dark matter consists of ordinary, baryonic matter, or else it consists of some more exotic form of matter. The history of the universe during the first few minutes provides an interesting measure of the total amount of baryonic matter in the universe that may help resolve the puzzle.
For a significant clue to the composition of the dark matter, we look to the abundance of the heavier isotope of hydrogen, weighing twice the mass, called deuterium, created during the big bang. There is no alternative source for the extra deuterium other than the big bang, since stars destroy deuterium rather than produce it. By now, a considerable fraction of any primordial deuterium present at the birth of the galaxy would have been destroyed inside stars. This is confirmed by observation: interstellar clouds contain deuterium, as do gravitationally-powered stars that have not yet developed nuclear burning cores; on the other hand, evolved stars have no deuterium.
To estimate how much deuterium was created in the big bang, one has to factor in all the deuterium that has since been destroyed. The percentage of the isotope destroyed since the big bang can be calculated if one knows the its rate of destruction, which can be found by comparing the abundance of deuterated molecules in the atmosphere of Jupiter with the abundance of deuterium in interstellar clouds. One has to choose a value for the density of baryons that cannot exceed about a tenth of the critical density for closure of the universe, or too little primordial deuterium would have been synthesized. Conversely, the density of baryons cannot be too low, below 2 or 3 percent of the critical density, or else one would overproduce deuterium, compared to what is observed in the solar system. If the universe is at critical density, 90 percent of the matter in the universe must be nonbaryonic.
If, in a universe at critical density, most dark matter could not be baryonic, what other forms could it take? Likely relics of the early universe are species of stable, weakly interacting particles. One example is the neutrino, if it possesses a small mass. Normally, the neutrino is assumed to be practically massless, but a finite mass is not implausible. There are so many neutrinos left over from the big bang that a neutrino mass of even 50 eV, or one ten-thousandth the mass of an electron, would suffice to close the universe. Laboratory experiments are underway in several countries to determine a definitive mass for the neutrino, but at present these experiments are inconclusive. The current upper limit on the electron neutrino mass, which is obtained from tritium decay experiments, is about 10 eV. Other species of neutrinos could have higher masses.
If the particles are very massive, possessing more mass than, say, a proton, a special name has been coined: the WIMP, for weakly interacting, massive particle. Exotic WIMPs such as the photino have been postulated to exist in sufficient quantity to close the universe. The problem is that there is no guarantee that these particles do exist. Disregarding this uncertainty, the big bang theory predicts their density today, if they do exist and are stable over the age of the universe.
The existence of the photino is predicted in a theory called supersymmetry. This theory doubles the number of known particles by postulating the existence of partner `-ino' particles. These particles are almost all short-lived, and exist in large numbers only in the very early universe, when the temperature was high enough to exceed the energy scale characteristic of supersymmetry, affectionately abbreviated to SUSY. As the universe cools, supersymmetry is broken. The relevant energy scale is not known from theory, but it must exceed 100 GeV to avoid conflict with particle experiments. In our low-energy universe today, the lightest supersymmetric particle should still survive. It is expected to be the partner, in the sense of having a complementary spin, of the photon, and is therefore known as a photino. Its mass is expected to be 10 to 100 times that of the proton. The photino is uncharged and interacts very weakly with matter.
There is strong evidence for SUSY from experiments at CERN that measure the strength of the nuclear interactions, which increase with increasing energy. There is no guarantee, however, that the weak and strong nuclear force strengths will all converge to the same energy. That they do converge at very high energy is the thesis of grand unification of the fundamental forces, whose breakdown in the very early universe gave rise to inflation. While this energy, some 10 to the 15 GeV, is very much higher than is directly accessible by experiment, the trend towards convergence of the disparate forces is already apparent. Only if SUSY describes the high energy world do these three fundamental forces become indistinguishable at a unique energy. Only therefore with SUSY could one construct a strong case for the inevitability of grand unification.
Despite the weakness of the photino's interactions, several experiments are being designed to search for this particle. These experiments are of four types. One uses particle accelerators, atom-smashing machines, to verify the particle's existence. The high-energy collisions in these machines normally produce jets of energetic hadrons, including particles and antiparticles that are ejected during the collision. So that momentum is conserved, the hadronic jets go off in two opposite directions, transverse to the collision direction. Although the weakly interacting photino would be invisible, it carries off momentum that must be balanced on the other side by a detectable jet. A one-sided jet would be evidence for a supersymmetric particle.
Sensitive laboratory detectors search directly for photinos in the galaxy's halo that have been intercepted by the earth and by the sun as the sun orbits the galaxy. Photinos that are trapped by the sun actually annihilate in its core. The heat they produce can slightly, but perhaps significantly, affect the sun's evolution. A byproduct of the annihilations is the generation of some energetic neutrinos that are quite distinct from those produced by the thermonuclear fusion reactions in the solar core. These high-energy neutrinos, as well as neutrinos produced by photino interactions in the earth, may be detectable in some of the underground detectors that are searching for solar and supernova neutrinos.
Radically different methods are used to search for the debris of photino interactions in the halo. Space or balloon-borne telescopes hunt above the earth's absorbing atmosphere for particles such as cosmic ray antiprotons and positrons produced in the halo by photino annihilations. However, cosmic ray protons interacting with heavy interstellar atoms also generate relatively low energy antiprotons and positrons. A way is needed to disentangle the two signals. Of course, the detection of a single heavier antinucleus, even antihelium, would be a phenomenal discovery and would require the existence of antistars and even antigalaxies. No such particles have been detected, needless to say. A similar strategy is to search for another relic of photino interactions; these are photons, specifically gamma rays, also produced when photinos annihilate in the halo.
The most natural form for dark matter is matter that we know exists, namely baryons. The big bang explanation of the light element abundances requires the existence of baryonic dark matter. Although these same abundances imply that most dark matter is nonbaryonic, the amount of dark baryonic matter is still most likely several times that in luminous baryonic matter, or about 3 percent of the critical density for closing the universe. But where do we look for the baryonic dark matter? One's first expectation might be that baryonic dark matter consists of burnt-out stars in the galactic halo, yet other forms, such as planets and black holes, are also possible. Baryonic dark matter does exist: it is far more uncertain whether there exists enough to solve any of the dark matter problems, that is to say, dark matter in galaxy halos, dark matter in galaxy clusters and superclusters, or dark matter in an amount suficient to close the universe. It is most unlikely that baryonic dark matter can account for the closure density, as we will now see: for this, one must appeal to WIMPs, or some other weakly interacting particle. However, baryonic dark matter is a serious candidate for dark matter at least in galaxy halos, if not on larger scales. In acknowledgment of the rivalry between these two forms of dark matter, the favored baryonic dark matter candidates have been dubbed MACHOs, for massive compact halo objects.
Among the possible astrophysical objects contained in the halo are the relics of stars, dim stars such as white dwarfs, neutron stars, or even black holes, as well as objects that have never quite fulfilled themselves as stars because of their low mass. Because these objects are invisible, or almost so, they are excellent candidates for dark matter. Moreover, MACHOs are more natural candidates for the halo dark matter than WIMPs, because they are already known to exist.
Two experiments reported in 1993 have found strong evidence for the existence of MACHOs. The technique used is gravitational microlensing. If a MACHO in our galaxy's halo passes very close to the line of sight from earth to a distant star, the gravity of the otherwise invisible MACHO acts as a lens that bends the starlight. The star splits into multiple images that are separated by a milliarc-second, far too small to observe from the ground. However, the background star temporarily brightens as the MACHO moves across the line of sight in the course of its orbit around the Milky Way halo. To overcome the low probability of observing a microlensing event, the experiments were designed to monitor several million stars in the Large Magellanic Cloud. Each star was observed hundreds of times over the course of a year. A preliminary analysis of the data, taken with both red and blue filters, revealed several events that displayed the characteristic microlensing signatures. The event durations were between 30 and 50 days.
The duration of the microlensing event directly measures the mass of the MACHO, although there is some uncertainty because of the unknown transverse velocity of the MACHO across the line of sight. The event duration is simply the time for the MACHO to cross the effective size of the gravitational lens, known as the Einstein ring radius. The radius of the Einstein ring is approximately equal to the geometric mean of the Schwarzschild radius of the MACHO and the distance to the MACHO. For a MACHO half-way to the Large Magellanic Cloud, that distance is 55 kiloparsecs. The Einstein ring radius is about equal to 1 astronomical unit, or the earth-sun distance. In order to be lensed, the MACHOs must be objects that are smaller than the lens, so they must be smaller than an astronomical unit, roughly the radius of a red giant star. The events detected are, to within a factor of a few, as the MACHO model of dark halo matter predicts, and the event durations suggest a typical mass of around 0.1 solar masses; however, there is at least a factor of 3 uncertainty in either direction.
Martin White
Professor of Physics
Professor of Astronomy
UC Berkeley
` Thanks for the article! It's a lot different than anything I've ever read about dark matter because here its nature is really called into question.
` I'll have to keep that stuff in mind! ...Maybe I'll have my boyfriend read it!
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