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## Most Beautiful Experiment in Physics141

Posted by michael
from the beauty-is-truth,-truth-beauty dept.
An anonymous reader writes "Robert P. Crease has concluded his poll asking what the most beautiful experiment in physics is. The winner was Young's double slit experiment performed using a single electron. Attentive readers will remember that Slashdot had a discussion of Crease's question previously, which Crease mentions in his current article." If you're unfamiliar with the experiment, Google pulls up a bunch of applets and demonstrations.
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## Most Beautiful Experiment in Physics

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• #### Simple != Simple (Score:2, Offtopic)

The beauty of this experiment is not just the effect that it generates but the way it simply demonstrates a complex phenomena. By complex I mean that it demonstrates that light travels as waves, until you fire only 1 photon then you prove it travels as particles as well.

Simple, brilliant and something that the more you learn about physics the more you learn about what the experiment shows.
• #### Re:Simple != Simple (Score:1)

Exactly!!

The slit thought experiment compares really well with Schroedinger's Cat as sublime in it's simplicity to convey an advanced Quantum Mechanics idea to someone without lots of math background.
• #### Re:Simple != Simple (Score:2, Redundant)

Um. Actually it was the Young's slit experiment with a single electron that won.

This shows that matter is made up of waves too. Everyone knew that light was made up of waves...

• #### Re:Simple != Simple (Score:1)

When you fire the one electron or photon, it's still a wave. This is unexpected bit, as with only a single electron, it has to go through both slits in order to create interference.
• #### Re:Simple != Simple (Score:3, Informative)

it demonstrates that light travels as waves, until you fire only 1 photon then you prove it travels as particles as well.

Actually, it proves that light travels as either a wave or particle.

It depends on the experiment. An experiment looking for particles will show particles, and waves, waves.

Check out The Copenhagen Interpretation [washington.edu]

I love Quantum Theory so much I read the same book three times: In Search of Schrodinger's Cat [2think.org]. Might be out of date, but an easy read for us lay men.
• #### Re:Simple != Simple (Score:2)

Actually, it proves that light travels as either a wave or particle.

Nope. Common misconception. Travels as a wave, arrives as a particle.

It depends on the experiment. An experiment looking for particles will show particles, and waves, waves.

True. But some experiments look for both. For example if you put a photomultiplier after Young's slits, you can literally watch the particles arrive (this was pointed out by Feynman).

And the interesting thing is, they only arrive where the wave doesn't cancel.

• #### Carver Mead vs. "Copenhagen Interpretation" (Score:1)

Feynman's student & colleague Carver Mead challenges the Copenhagen Interpretation in his book "Collective Electrodynamics" - a very different way of thinking of quantum theory.

An interview with Mead about his book & ideas:

http://www.spectator.org/AmericanSpectatorArticles /carver.htm

As an enthusiast rather than someone educated in physics, I would like to hear what you guys think about the validity of his arguments.

• #### Re:Simple != Simple (Score:1)

Has anyone considered that they exist only as particles, and any wave function assigned to them exists because of inherent vibration? Sometimes the wavelength of the vibration exceeds the width of the particle, but so what?
• #### no WAY!!! (Score:5, Funny)

on Friday August 30, 2002 @07:42PM (#4174338) Journal
the most beautiful experiment is, has been, and always will be the practical aspects of

* photons gets converted to electric impulses;
* these electric impulsese are stored, usually by dielectric tunneling, into a floating gate (Flash memory)
* the information is then read back, sent through 7 (read it, it's SEVEN) layers of network stack, to a physical link
* the data is digitized into more packets of light, and sent across the atlantic from RUSSIA to the US.
* after more routing (some in light-packets, some in electrical), it climbs back up the 7-layers.
* mozilla interprets them, and through some seriously complex transistor networks, the signals cause some polymers to twist just the right amount
* and i see some pr0n.

wait a sec; that would probabbly be "the most beautiful engineering feat"... ahh fsck it.
• #### Re:no WAY!!! (Score:1)

the information is then read back, sent through 7 (read it, it's SEVEN) layers of network stack, to a physical link

*boggle* You've figured out a way to unite the OSI model with the Real World at least well enough to run Mozilla over it? Color me impressed..

• #### WOOHOO!!!! (Score:2, Interesting)

My comment on the Slashdot thread [slashdot.org] made it into the article!

Why, I do believe that this is the first time I have ever been published. Thanks, guys!

Blockquoth PhysicsWeb:

My original article was also mentioned on Slashdot.org, an extremely active website. Although Slashdot bills itself as "news for nerds", its audience evidently includes a large number of science-history aficionados. A discussion with more than 500 comments ensued, many dissecting the merits of particular experiments. Here too the double-slit electron-interference experiment topped the list. One participant remarked that this and other experiments illustrating quantum-mechanical principles "even seem to reveal something about ourselves", noting that "philosophers and cranks are attracted to the results like moths".

Other Slashdot participants proposed many of the same experiments as Physics World readers - and often for similar reasons. However, they also came up with an imaginative variety of examples of deep play. These included fun things like putting discarded CDs into microwave ovens, firing potatoes using lengths of pipe and cans of hairspray, and synchronizing coloured lasers to the music of Pink Floyd.

One of the contributors described watching small plastic bags circulating in wind pockets, commenting that "sometimes there's so much beauty in the world, I just can't take it". Another mentioned the fact that a hunter firing at a falling monkey always hits the monkey no matter how far away it is, even though it drops just as the hunter fires. One person even cited sitting outside a hospital to hear the Doppler effect, with the comment: "Anytime an ambulance passes me, I'm amazed."

One Slashdot participant described a method of producing a fractal using a coin, marker and tape measure, claiming to have nearly cried the first time they saw it. Another described an impromptu game that he and classmates had invented at the end of a lab class, in which a liquid-nitrogen-filled styrofoam cup with holes in the bottom can be made to glide pleasingly around the floor when kicked about as the gas leaks out.

• #### Re:WOOHOO!!!! (Score:1)

Quoting you, quoting him:

One of the contributors described watching small plastic bags circulating in wind pockets, commenting that "sometimes there's so much beauty in the world, I just can't take it".

It certainly doesn't read as though he got the joke [slashdot.org].

• #### Re:WOOHOO!!!! (Score:2, Funny)

"One of the contributors described watching small plastic bags circulating in wind pockets, commenting that "sometimes there's so much beauty in the world, I just can't take it"

Proving the physics crowd needs to get out to the movies more often [imdb.com].
• #### Re:WOOHOO!!!! (Score:1)

cool, now you can sue them for \$5,000,000!
• #### Re:WOOHOO!!!! (Score:5, Funny)

<awh@awh.org> on Friday August 30, 2002 @08:59PM (#4174632) Homepage
Although Slashdot bills itself as "news for nerds", its audience evidently includes a large number of science-history aficionados.

I love how this sentence is written as if it's some sort of contradiction.

• #### falling monkeys (Score:2)

surely if the monkey is far enough away then the time that the light indicating the start of the fall takes to reach the hunter will cause him to miss high? it would also seem that the curvature of the earth would cause the hunter to aim low. surely these two effects don't cancel each other out completely?
• #### Re:falling monkeys (Score:1)

just how far can you see son?
• #### Re:falling monkeys (Score:2)

well another question could be how accurately could I shoot, or how good are my reaction times, or even how much is the line of fire refracted by the atmosphere. but that not really the point is it?
• #### Re:WOOHOO!!!! (Score:2)

Hovercup! That was the greatest comment ever.
• #### That's an easy one..... (Score:2, Funny)

Any demonstration that makes the lesson sink in to a student's head.

Kudos to one of my physics professors, Dr. Richard Mancuso, for his toy collection. Any student that brought him a toy that clearly demonstrated a principle of physics for that wasn't already in his collection got extra credit for the semester. I clearly remember the collection filling a few display cabinets, and there was at least one toy for every lecture. I learned 10 times more in his course than I did the previous semester with another instructor because he made it interesting.
• #### My favorite Physics Experiment (Score:3, Interesting)

on Friday August 30, 2002 @08:08PM (#4174440)
Measuring the speed of light.
For our experiment, we used a mirror set up to rotate at 6000 RPM. A laser is aimed at the rotating mirror, bounces about 20 meters across the room and back. The theory is that the rotating mirror will slightly rotate by the time the beam of light returns to the rotating mirror. Even at 6000 RPM, the mirror only rotates a very small amount, but enough for the laser's endpoint to change a few fractions of a mm.

By knowing the displacement between the endpoints of the laser at 6000 RPM and 3000 RPM, we could easily calculate the angle that the mirror rotated from the initial path to the return path across the room. Using this info, we solved for the time required for it to rotate that angle. That is the time required for the Laser to travel across the room and back. The distance:time ratio is the speed of light. Mad props to the dude/chick who designed that experiment.

• #### Re:My favorite Physics Experiment (Score:2, Interesting)

It was Jean Foucault who designed that experiment, and in 1862 he came up with a figure of 298,000,000 m/s compared to the current SI definition of 299,792,458m/s

He also demonstrated in Paris in 1851 that the earth did indeed revolve upon it's axis, by using a large pendulum. (Of course, people in 1851 had generally accepted that the earth did revolve around an axis, but this was the first physical demonstration of the effect of such rotation)
• #### Re:My favorite Physics Experiment (Score:1)

Has the meter been redefined to make the speed of light 300,000,000 m/s? The difference is only 692 microns (in terms of the "old" meter).
• #### Re:My favorite Physics Experiment (Score:1)

No, It has been redefined min 1983 to make the speed of light the value mentioned by ColaMan, see here [nist.gov].
• #### physics makes me gaga (Score:1, Offtopic)

i have to say that physics, especially on the quantumn level, is the most interesting science I know of. there are others that are fascinating but nothing gets to the heart of everything like physics. can i get an amen? :) the slit experiment, when I first read about it in some layman's guide to physics just floored me with its simplicity and easy understandability.
• #### HUZZAH FOR QUANTUM WEIRDNESS!! (Score:2)

No wonder this one won. ( wun wun? ) It is an elegant, easy to understand set-up with REALLY weird results. Something to smack your macro-world "common sense" upside the face.

"Like, huh? It's interfering with ITSELF? Like, is it a particle, or a wave, or what, teach?"

I think some of the crazy new laser "faster than light" experiments could probably give it a run for the money, but they are a lot harder to understand. There is nothing quite like the quantum world jumping up through your apparatus and presenting itself in all it's non-Newtonian glory.
• #### Re:HUZZAH FOR QUANTUM WEIRDNESS!! (Score:2)

Or what about the fact that observing it changes the past. It was a particle if observed before the slits, a wave afterwords. Thus, when it left the source, it had to be one or the other.

This gets especially freaky on the astronomical scale, when you have to large gravity sources widely separated that bend light back, like slits, from an even further distant light source. If you look for the particles from the distant star, it will come to you in a straight line. If you look for the wave pattern, it goes wide and around both(!?!!) gravity slits and shows up as an interference pattern... Thus, by observing, you made the photon that left the start billions of light years away either be a particle or a wave for all of its existance, though it wouldn't know which one to be unless you looked at it.

Freaky.
• #### Re:HUZZAH FOR QUANTUM WEIRDNESS!! (Score:1)

by observing, you made the photon that left the start billions of light years away either be a particle or a wave

This is what really peeves me about particle physicists. This makes absolutely no sense, and WILL NEVER MAKE SENSE if people continue to think about it in such an asinine way.

What the hell is the variable here? Is it me? Because if I damn well don't "observe" the particle then we have no fucking way of knowing whether it fits into our pre-conceived notions of how a "particle" or a "wave" should act.

If we agree that the "observer" plays no part in the experiment, and, furthermore, if he does, it's not a properly constructed experiment, then we shouldn't immediately assume (without any evidence, mind you) that the metaphysical act of "observing" plays any part in the "existence" of the photon, especially when the "observation" occurs AFTER the photon was created.

This is the most half-baked theory in all of physics, and people go around repeating it as though it were bible-fucking-truth. Just admit it: Einstein was right, God doesn't play dice.

• #### Re:HUZZAH FOR QUANTUM WEIRDNESS!! (Score:1)

Just admit it: Einstein was right, God doesn't play dice.

Yeah, he's more of a Blackjack guy.

• #### Re:HUZZAH FOR QUANTUM WEIRDNESS!! (Score:1)

>Einstein was right, God doesn't play dice

God does indeed play dice, and they are loaded... :)

• #### Re:HUZZAH FOR QUANTUM WEIRDNESS!! (Score:1)

ack! I thought I had gotten away from alpha centauri references! :-p
• #### This is one of the really cool ones... (Score:1)

For those with maths, Messers Wolfram [wolfram.com] tell all. I like this one.

This experiment shows off wave/partical duality (it even has cool terminology). The cool bit about physics (yeah, it has cool bits) is the things it takes your head a while to get around.

OK, background: waves spread round corners. Think of a wave at a harbour mouth. The closer the gap is to the wavelength of the wave, the better it spreads (look up diffraction [wolfram.com]) (troll me, I know this is a gross over-simplification) - ever think about how you can hear but not see round corners? Light == really short wavelengths (nanometres), not like door width lengths (m) (doesn't bend well round the corner), sound == long wavelengths, kinda door-width like (m/cm ish) (bends very well round the corner).

So you get two bits of card with a light behind them, and a screen to shine light through them onto. The first card has one slit, so it shines a little line of light onto the second.

The second has two parallel slits in it, within range of the spread of light, and the light that gets through the first card onto a slit in the second card makes it to the screen.

Now the cool bit.

You get a ripple of light on the screen. Not a black screen. Not two lines showing up the second card shape. Ripples [phys.ethz.ch].

Now, modern physics can explain this. It's the wavefront from the first slit (think ripple hitting a harbour mouth) that spreads out in a circle and hits the next two slots, starting another ripple on the other side of both.

At the far wall, you get points where the peak of a wave from one slit hits the peak of a wave from the other, and you get a really tall peak. Or a trough and a trough, and get a really low trough.
• #### Re:This is one of the really cool ones... (Score:2)

Comparing sound doesn't really help though.. that's a totally differnet thing. Totally different kind of wave in a totally different medium.. does the same thing even apply?
• #### Re:This is one of the really cool ones... (Score:1)

It does apply. You get the same thing with sound - noisy spots and quiet spots as you walk round the far wall if you do the same thing with sound.

Same physics. Still is a gross generalisation, tho.
• #### Okay (Score:2)

You forgot to mention.

The cool part of the experiment is when you start sending that light 1 photon at a time, so we can demonstrate that individual particles are being sent. The diffraction pattern STILL appears... so we end up with a particle interfering with itself.

Now, as people view light as some kind of weird beast.. the experiment is even more exotic when done with an electron beam. Done with single electrons, which we REALLY think of as particles, we still get the diffraction pattern. That's where things get really weird.
• #### well done! (Score:1)

i thought that google search would come up with a heap of pr0n sites!
• #### eddington (Score:1, Offtopic)

The double slit is great. I might vote for the 1919 experiment of Eddington, which verified General Relativity, showing that the mass of the sun bent the path of light. A sweet verification.

just a simple physics student's comment.
• #### I like the Pound-Rebka Experiment (Score:2, Interesting)

They dropped photons off the roof of a building and measured their blue shift at the bottom, confirming general relativity. One description of the experiement is here [gsu.edu].

Pound is an interesting guy. He experimented with using microwaves to heat people instead of wasting energy heating entire buildings. He tested it out by rigging his microwave oven to operate with the door open. He told me that he had to bypass three interlocks, but that he got it working: there was a nice warm glow, like standing in front of a campfire.

Needless to say, don't try this at home unless you're a damn competent physicist.
• #### Ugh, Double Slit? (Score:1)

What a boring experiment that was.

The prettiest experiment has to be Milliken's Oil Drop.

• #### My favorite beauty (Score:2)

Shroadinger's Peacock.
• #### Nothing lighter than C60 (Score:2)

Beautiful as it may be with a single electron, or photon, or whatever. These have almost no mass. When done with buckeyballs, the double-slit experiment acquires an amazing beautyl.
• #### Quantum Polaroid Demonstration (Score:2)

We have an educable station that plays Mechanical Universe documentary lectures from the mid eighties. You can read more about those at:

http://www.themechanicaluniverse.com/

Highly recommended. The best demonstration I ever saw on that show involved three light polarizers. The setup was three polarizers on optical stands with a lamp shining through all three. That is, all three in the same orientation so the light shines through. The third is turned through 90 degrees and of course blocks the light of the lamp from the screen. Dr. Goodstein then turns the second middle filter through 45 degrees and almost half the light makes it through the screen. The result is completely counterintuitive and is an excellent and easy macro scale demonstration of quantum principles.
• #### Re:Quantum Polaroid Demonstration (Score:4, Funny)

on Saturday August 31, 2002 @12:14AM (#4175208) Homepage Journal
I once heard the three polarizer experiment described as follows.

You have a field with cows. To make sure that now cows get out, you put up two fences. They stay in their field. But you're really paranoid, so you put a third fence in between the two. Now, all of a sudden, one fourth of your cows are wandering in your neighbor's field.
• #### My Choice... (Score:1)

Ryan Geiss' Smoke plugin for WinAMP which started life as a fluid-modeling program...

Jaysyn
• #### And what about thought experiments? (Score:1)

Schroedinger's cat will live forever.
• #### challenging our sense of reality (Score:2, Interesting)

I am quite disappointed that Michelson-Morley did not make the top ten. Most experiment on this list challenged our vision of reality. Young help illustrate the particle/light duality. Galileo showed us that acceleration does not depend on the mass of the falling object. Newton showed that light was made a composite of individual entities. Rutherford refuted the muffin theory of the atom.

Likewise, Michelson-Morley refuted the traditional hypothesis of the Ether(or aether). This concept was a kludge used to validate various assumptions. At that time, it was assumed that light needed a medium, and Ether was as good an explanation as any. By creating a beautiful experiment to refute the ether, Michelson-Morley forced scientist to study the problem instead of just making assumption. Progress is made when our fundamental assumption is proven false.

That does not mean that measuring physical constants is not beautiful experimentation. Certainly Foucault and Eratosthenes and Cavendish and even Milikan are great experiments which are instructive even now. But were they earth shattering pieces of experimentation. I do not know.

• #### wierd science hands down! (Score:2)

i always though the most beautiful experiment was creating kelly lebrock in wierd science!

chips, dips, chains, whips, sex, drugs, rock and roll... your average party.

• #### Most Beautiful Thought Experiment. (Score:2, Interesting)

How about a poll for the most beautiful or insightful thought experiment in physics?

Hacker types usually deride gedanken (thought) experiments as exemplified by Eric Raymond's idiotic Jargon file entry for 'gedanken'. So be warned: do not read ahead if you cannot appreciate the importance of theoretical work in physics or elsewhere.
Everyone knows the Schrodinger's cat and the Einstein's elevator experiment. By the way, if you put the Schrodinger's cat inside Einstein's elevator, would that lead to a theory of Quantum Gravity? Jokes apart, these thought experiments have also been influential:

1. The Einstein-Podolosky-Rosen or EPR Paradox: http://roxanne.roxanne.org/epr/einstein1.html
2. Maxwell's Demon
3. Object nearing a black hole
4. Feynman's QED thought experiment: what would happen when you shine light at an object passing through an interferometer, a device that can split the object into a pair of wavelets which are later recombined to produce an interference pattern. This incidentally was converted to a real experiment by an MIT team: http://www.aip.org/enews/physnews/1996/split/pnu25 3-2.htm
• #### Re:Most Beautiful Thought Experiment. (Score:1)

EPR is no longer a thought experiment, Alain Aspect implemented it in the 80's, see:

http://www.scispirit.com/Resource/aspect_experim en t.htm

BTW this experiment proves EPR wrong, and is definitely on my list of most beautiful ones.
• #### HAHA (Score:1)

"One of the contributors described watching small plastic bags circulating in wind pockets, commenting that 'sometimes there's so much beauty in the world, I just can't take it' "

I wonder if he knows the reference which this is from and is just joking or what. If not thats damn hilarious.
• #### most beautiful physics website (Score:1)

I don't know about experiments, but for a physics website http://britneyspears.ac/lasers.htm [britneyspears.ac] is pretty good!

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