Naked Science Forum
General Science => General Science => Topic started by: ukmicky on 01/10/2005 17:14:16
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I was bored last night, and for some strange reason thought i would teach myself a bit of Quantum physics.(LIKE WE ALL DO)[:)]
Anyway after about an hour of looking i came across a web site that had an article about an experiment showing how just by observing the experiment you can change its results . i found the experiment a bit hard to believe,because it would be so amazine if it were true.
SO CAN ANYBODY TELL ME,IS THE BELOW EXPERIMENT REAL (the last two paragraphs are the interesting bit)
Michael [:)]
Experiments were done at the National Institute of Standards and Technology by a group of physicists. They captured 5000 atoms of Brillium and put them in a vacuum, irradiated them with radio waves so that they got hot, and then they shined laser light on them. Now normally, when atoms are warm or hot or have energy, when laser light shines on them, it gets scattered. So you can observe through the scattering of the laser light that the atoms indeed are hot or have absorbed radio energy. And it takes approximately a quarter of a second for all. If you start shining radio waves in the midst of these atoms, it takes about 1 quarter of a second for roughly all of them to absorb radio energy. So if you shine laser light through and none of them had absorbed the radio energy, the laser beam would go right through. If all of them had absorbed radio energy, there would be a lot of scattering. IF only 50% of them had absorbed the radio energy, then you would have a 50% scattering pattern. In other words the scattering pattern will tell you how many atoms had absorbed the energy.
Ok, now, if you radiate the atoms and then don't shine the laser light until a quarter of a second later you see that virtually all of them are hot. On the other hand, suppose you decide to shine the laser light in half way along the quarter of a second path. In other words, half of a quarter second, about an eighth of a second, you decide to shine the laser light in and look. What would you expect to find? Well you would expect to find at least half the atoms had absorbed the energy because it takes a quarter of a second for them all, so roughly half. And that's about right. So you get a scattering which tells you about 50% have indeed scattered. So nothing surprising there.
But now the next quarter of a second passes and now what would you expect to find? Well most people would expect to find that by now, all of them had absorbed the energy. But that is not what happens at all. Only 2/3 of them have absorbed the energy. So you don't get them all. By simply looking in one time, you've affected the final result.
Now what happens if you decide to look in not only at 1/8 of a second but at 1/16 and 1/32 and 1/64, and 1/128? The very smallest fractions of a second so that you are looking in so often that you are looking in maybe 256 times in ¼ of a second. Well what happens in this case is rather amazing. If you look in that often, what you find out, that none of the atoms have absorbed any of the radio energy. In other words, by simply watching diligently enough, you've kept the atoms from absorbing the energy - even though the radio energy was on all that time. So what this proves is that a quantum watched pot doesn't boil. So the old adage is true. Quantum pots watched diligently enough won't boil. And that's exactly what happens. And none of the atoms boiled. None of the atoms absorbed any of the energy. Providing one looked, long, rapidly enough along the pathway. So this essentially shows that observation can affect the physical world.
Michael (https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fi11.photobucket.com%2Falbums%2Fa186%2Fukmicky%2Frofl.gif&hash=481319b762ee9d57cda15e90d2e83ee6)
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Fascinating stuff Michael...thanks for the great post.
Isn't this all related to the Schrödinger's cat thing ?
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The experiment sounds reasonable enough. Shining a laser light through excited atoms is a serious disturbance to them. I am not at all surprised this modifies the result. Actually, it is one way to get stimulated emissions from atoms in an excited state.
The comparison to Schrodinger's cat is not exact. That case was really hyperbole, an example that Schrodinger contrived to show that QM could give ridiculous results. The photon may reflect or transmit through the half-silvered mirror, and we cannot say which it will be, but when it does, the result will be certain. The cat will live or die, and we do not have to open the box to determine the outcome. I'm sure Schrodinger meant that to be the point. Things happen all the time in the universe, without any human observation. I'm afraid we just aren't that important.
"F = ma, E = mc^2, and you can't push a string."
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Michael,
I've found another site about this specific experiment which looks interesting/informative. See the first piece on this web page:
http://www.dhushara.com/book/quantcos/zenq/zenoq.htm
The fact that you find this result unbelieveable suggests you've not been exposed enough yet to the weird world of quantum physics! Some of my favourite quotes on the subject are:
Neils Bohr (considered the "father" of quantum physics): "Anyone who is not shocked by quantum theory has not understood it."
Feynman: "Anyone who claims to understand quantum physics is lying."
Schrodinger (yes, he of the wave equation that underpins the whole of quantum physics): "I don't like it, and I wish I'd never had anything to do with it!"
I think the best introduction to the weirdness of quantum theory is the double slit experiment. See:
http://www.upscale.utoronto.ca/GeneralInterest/Harrison/DoubleSlit/DoubleSlit.html
(For anyone who, like me, prefers books to websites, I can recommend some good beginner / layperson books on the subject.)
Solvay.
1.618033989 - everyone's favourite number!
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quote:
Originally posted by Solvay_1927
Michael,
(For anyone who, like me, prefers books to websites, I can recommend some good beginner / layperson books on the subject.)
YES PLEASE !!
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Oooh, where to start ...
The first book I read that gave a really useful beginner's introduction is "Great Ideas in Physics" by Alan Lightman. This uses simple explanations (and a little basic school maths - nothing difficult) to help you understand the basics of quantum physics (and also of special relativity, conservation of energy, and entropy).
The best book I've read specifically on quantum theory is "QUANTUM" (subtitle: A Guide for the Perplexed) by Jim Al Khalili - well written, requires no prior knowledge (and contains no maths at all), lots of colour pictures (I'm being serious - the pictures really help when you're talking about something as strange as QM) - it takes you through the history of QM, the practical applications and uses (from CD players to futuristic quantum computers) and the philosophical difficulties (i.e. the different interpretations of what it all means).
Then there's "QED: The strange theory of light and matter" by Richard Feynman - a nice short (and therefore cheap) collection of 4 lectures he gave to a non-scientific audience. Excellent - it's classic Feynman.
(I've never seen his full 3-volume "Feynman Lectures on Physics", but when I'm rich I'll definitely buy a copy. Apparently the 3rd volume is mainly about quantum physics.)
Also, "In search of Schrodinger's Cat" by John Gribbin is really good - a very good author, very interesting and reasonably comprehensive book. (He's also written a follow-up / update called "Schrodinger's Kittens" - neat name - but I've not read that yet.)
And "Quantum Theory: A Very Short Introduction" by John Polkinghorne is reasonably useful.
A couple of other books I can recommend which cover all of physics (not just QM) are:
"Galileo's Finger" by Peter Atkins - the top 10 ideas in science - really well written and interesting, very up to date, quite in depth and challenging (considering it's only a brief overview of the whole of science).
"Great Physicists" by William Cropper - a hefty book giving biographies of about 30 of the greatest physicists of all time - really interesting biographies, but it also gives a reasonable taster / introduction for the actual physics involved too.
Oh, and of course there's "The New World of Mr. Tompkins", an update of the classic "Mr. Tompkins in Paperback" by George Gamow (covering relativity, quantum particle physics, etc).
Anyway, if you go down your local library (like I did - it's cheaper than buying them) and read all these books, you too can become a sad anorak like me who thinks he can fool people on a physics discussion forum into thinking he knows what he's talking about.[:I]
Happy reading.
Solvay.
1.618033989 - everyone's favourite number!
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Oh..I've changed my mind now...no thanks [;)]..
seriously though (if i can be serious for a minute)..thanks Paul....which one of these excellent tomes would you recommend as being the very easiest read ?...(that's my level and I'm happy to stay there)...would it be "QUANTUM" (subtitle: A Guide for the Perplexed ?....sounds like it's your fave.
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Yeah, "Quantum".
"Great Ideas in Physics" is even easier as a first-step introduction, but not very comprehensive.
The reason I listed a number of books (other than the fact that I found them all useful) is in case you can only find one or two of them (in the library, Oxfam 2nd hand bookshop, etc).
Of course, if you're saying that money's no object for you, then I suppose you can just buy all of them (you rich b*****d).
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thanks Paul,i shall have a look the next time i take the wife down the book shop.
Michael (https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fi11.photobucket.com%2Falbums%2Fa186%2Fukmicky%2Frofl.gif&hash=481319b762ee9d57cda15e90d2e83ee6)