Another weird Physics Question

JOS/EFR ^ | 07/21/2003 | Monty22

[Monty22]

Well the answer is that the photon travels as a wave and does somehow manage to do what seems quite impossible and go through both slits and interfere with itself. If we cover one slit then we know which one it goes through and indeed the interference patterns vanish. Even more strange is the fact that it we put a detector on one of the slits to tell us whether the photon goes through that slit or the other one then the interference pattern vanishes. The act of observing the electron makes its wave nature collapse into a particle.

The nature of light really is strange! But this behaviour is not limited to photons of light far, as de Broglie predicted, electrons behave in exactly the same way. Although the Copenhagen interpretation seems completely vindicated by this experiment, it is still philosophically difficult to accept. It now appears that we, as observers, affect the way that light behaves. Would light always be a wave if nobody was there to observe it? If a dog observes the photon will its wave function collapse? This will lead us to deep philosophical questions and eventually we will be forced to ask whether the universe only exits because there are intelligent beings to observe it. We will not pursue this fascinating line any further.

[Monty22]

*heavy duty Quantum light physics*

Ok, I do want to discuss it further some..

Now I had heard of the interfernce experiment plenty of times with the two slits. For some reason, I had not heard the part where a detector on one of the slits will cause the wave form to collapse into particle.

Now what I'm wondering, does the detector itself cause it, or is it our measurement of that detection? If it's the former could you setup a computer to do all the collection of data, and not look at the results, just have the computer know? What if you looked just to make sure the data doesn't change? Would that collapse the wave?

If it's the latter, and only collapses when a living thing views it, would it simultaniously collapse if you stored the data on cd's in seperate parts of the world?

The 'data' I mean is the results of which slit the photon traveled through. I know this has analogues to "schroedinger's cat", but I also wanted to discuss what would it mean if humans (or dogs, cats?) are required for light waves to collapse.

[Damocles]

...go through both slits and interfere with itself.

As a lad, I was told I'd go blind if I didn't stop interefering with myself. Some photons have all the luck...

[Revelation 911]

hold my handlotion alert

[VadeRetro]

Any interaction at all with anything absorbs the photon and collapses the wave function.

The perhaps best-educated guess as to what is going on: John Archibald Wheeler thinks the real nature of the photon is elusive to our ability to sense it. It's something sort of in-between that we cannot detect directly; we can only detect wave phenomena or particle phenomena so it looks at times like one and at times like the other.

[Monty22]

I suppose the Heisenberg uncertainty principle helps a lot with this issue.

On that site there is also a story about Lene Hau:

http://www-groups.dcs.st-and.ac.uk/~history/Mathematicians/Hau.html

The incredible part is: "The reason for the behaviour of the Bose-Einstein condensate is essentially due to the Heisenberg Uncertainty Principle for at such low temperatures the momentum of the atoms is known accurately so their positions cannot be accurately known so, in some sense, spread out. Hau produced slow light by inducing quantum interference in the condensate. "

[petuniasevan]

PING for your expertise on the subject.

[VadeRetro]

If nothing else, it's another example that nature is weirder than you tend to think.

[AntiGuv]

Quantum kitty placemarker!

[bondserv]

A well known Senior Stanford Research Physicist's take on light.

Article here.

[LiteKeeper]

read later

[KansasConservative1]

"whether the universe only exits because there are intelligent beings to observe it."

If a man is alone in a forest (away from his wife) is he still wrong.

(I am a man by the way ;-)

[Ole Okie]

As a lad, I was told I'd go blind if I didn't stop interefering with myself. ...

Well, did you?

Or did your hairy palms keep the blindness away?

[Nick Danger]

How many Heisenbergs does it take to change a light bulb?

If you knew the answer, you wouldn't know where the light bulb is

[Damocles]

Type slower...the braile reader is malfunctioning...

[Monty22]

Good article..

"Furthermore that the speed of gravitons is apparently some ten orders of magnitude higher than the current speed of light."

Whoah.. That'll really mess some stuff up.

[Outlaw76]

From the website you linked with Hau's work:

"She is famous, not for the work of her thesis but, rather, for her later experiments to slow down light. On 18 February 1999 the journal Nature selected for its cover article the paper Light speed reduction to 17 metres per second in an ultracold atomic gas written by Hau in collaboration with Stephen Harris of Stanford University and two Harvard graduate students Zachary Dutton and Cyrus Behroozi. Later work resulted in slowing light to about one mile per hour, then in 2001 her team were able to stop light for one-thousandth of a second. Hau said:-

... this is an amazingly long time. But we think it can be stopped for much longer. It's nifty to look into the chamber and see a clump of ultracold atoms floating there. In this odd state, light takes on a more human dimension; you can almost touch it. "

WOW! If this is true, and I haven't the knowledge to claim it false, I was traveling at 80C on my way to work this morning! No wonder I was feeling particularly massive... I thought it had something to do with the cream filled doughnut.

[Monty22]

I wish there were pictures of what this 'stopped light' looked like.

Wouldn't it be invisible, not emitting any protons? Her descriptions of it sounds like it looks like an angel or something though. How is it possible to 'see' stopped light?

[AntiGuv]

How is it possible to 'see' stopped light?

I'm going out on a limb here, but would not other light waves still bounce off the 'stopped' light, or something like that?

[FreeAtlanta]

lol, yeah, I am feeling kind of massive myself.

[TheBigB]

I know someone who might be able to help...*pings*