An electron in two places at the same time?!?

[Rosanella]

Now that my maths exam is over, I'm finally catching up with books of various sorts that have been waiting my attention for months.

Whilst reading Lisa Randall's and Michio Kaku's books, I've learned that an electron can be in two places at the same time. How does that work out? :shock:

How are experiments carried out to establish that the electron in question is the same one? :scratch:

[thing]

I'm sure someone educated will be along shortly but from my v.limited knowledge of quantum theory it's probably (see what I did there....) to do with the probability of where it is. As soon as you observe it the probability wave collapses and it's in one place. Until you do observe it though it could be in a number of places with receding possibilities for each one. Also you can measure the velocity of an electron and it's position, but you can't do them both at the same time.............weird stuff indeed.

Edit: Don't get caught out by thinking of an electron as a particle that whizzes around the nucleus of an atom like a planet whizzes around the sun, that went out of the window ages ago.

[themos]

Do yourself a favour and read "QED - The Strange Theory of Light and Matter" by Richard Feynman. If you don't understand it after that, you never will.

[thing]

I'm most of the way through 'The Fabric of the Cosmos' and that's enough for one lifetime......... :shock:

I think it was Neils Bohr who said 'If you think you understand quantum physics you don't.'

[themos]

"I think I can safely say that nobody understands quantum mechanics." [removed word] Feynman, again.

Also "If I could explain it to the average person, it wouldn't have been worth the Nobel Prize.

[themos]

Thirty-one years ago [1949], [removed word] Feynman told me about his "sum over histories" version of quantum mechanics. "The electron does anything it likes," he said. "It just goes in any direction at any speed, forward or backward in time, however it likes, and then you add up the amplitudes and it gives you the wave-function." I said to him, "You're crazy." But he wasn't.

Freeman J. Dyson, 1983

(from wikipedia)

[Rosanella]

...

Edit: Don't get caught out by thinking of an electron as a particle that whizzes around the nucleus of an atom like a planet whizzes around the sun, that went out of the window ages ago.

Yeah, I've gone past that one a while ago

I understand that a particle can be in different probable places, but in what way is a particle in two places at the same time?

As a waveform?

[starf]

quanta can be thought of as having both vector and waveform functions. thomas young's, double split experiments showed how a monochromtatic light source when shone through two parallel slits produced an interference pattern. The phenomenon which allows tunnelling also accounts for systems in which energy levels are seen to overcome an impedance higher than the energy level of the particle.

http://uk.youtube.com/watch?v=DfPeprQ7oGc

[acey]

Shine a thin beam of light at a mask with two narrow vertical slits close together and instead of getting an image of two slits on the other side you get an interference pattern showing many vertical bands, the brightest at the centre. This is the experiment Young did in 1800 or thereabouts which shows light to be wave-like.

Now turn down the intensity of the light source. As Einstein proved theoretically in 1905, you eventually (in theory) reach a point when the beam can't get any fainter, instead it breaks up into intermittent pulses of equal brightness. (In reality you can't turn down an ordinary beam so much without switching it off altogether but let that one pass).

What you find is that even when light consists of these intermitent pulses (aka photons) you still get an interference pattern, though it's now built up slowly over time. So individual photons are still somehow behaving like the waves that were going through both slits at once. In other words a photon appears to be able to be in two places (passing through two slits) at once.

Now substitute a beam of electrons. Same thing. (I think this was first done by a guy called Thompson, son of JJ Thompson who discovered the electron, in Aberdeen - so hooray for Scottish science).

Note that the photon or electron *behave as if* they're in two places at once. If you actually try to observe them going through either slit then the effect goes away: you no longer obtain an interference pattern.

Andrew

[themos]

but in what way is a particle in two places at the same time?

it's actually in an infinite number of places, at the same time. But if you manage 2, infinity should be a doddle.

[RobH]

Don't mention quantum entanglement....that's when it gets really wierd

Rob

[EA2007]

Now that my maths exam is over, I'm finally catching up with books of various sorts that have been waiting my attention for months.

Whilst reading Lisa Randall's and Michio Kaku's books, I've learned that an electron can be in two places at the same time. How does that work out? :shock:

How are experiments carried out to establish that the electron in question is the same one? :scratch:

Werner Heisenberg and his Uncertainty principle stipulates that a particles movement and position cannot be found, as the closer you are to finding one, the further you are from the other.

For those of you who like film, there is an interesting mini-documentary called 'Copenhagen' regarding the matter and it stars Daniel Craig (Bond, Layer Cake) as Heisenberg and Stephen Rea (V for Vendetta) as Neils Bohr.

[themos]

"How are experiments carried out to establish that the electron in question is the same one?"

To deal with this technical issue, I think that researchers use a controllable source of electrons. As you turn down the flux you reach a stage where you are sure that only one electron is in the apparatus at a time. And then you see that it interferes with itself being in many places and ends up where wave-mechanics predicts as opposed to particle mechanics.

[acey]

but in what way is a particle in two places at the same time?

it's actually in an infinite number of places, at the same time. But if you manage 2, infinity should be a doddle.

"Actually"? Or virtually?

[themos]

heretic! do you doubt the existence of the path integral?

[acey]

No, only the paths. Thing I've never understood - if a photon really could get from a light bulb to my eye via Alpha Centauri, how long would it take? If it's 8 and a bit years then what's it doing in the sum?

[themos]

for the photon, it takes no time at all. the paths are not constrained to satisfy the classical equations of motion, they are "off-shell", I hope I'm remembering this right.

[acey]

But if a photon was really in two places "at the same time" it would seem to imply an actual time as well as an actual position. Off-shell particles are virtual, not actual. People such as Hawking interpret them as real in a many-worlds sense, but then you get the sort of problem I'm talking about: you need to believe in a world where the classical equations don't hold.

Not sure if I'm remembering right either but it has always puzzled me. How is a photon meant to know if it's real or virtual (ie if it's an interior wiggle on a Feynman diagram or an external one)?

[ChrisEdu]

To deal with this technical issue, I think that researchers use a controllable source of electrons. As you turn down the flux you reach a stage where you are sure that only one electron is in the apparatus at a time. And then you see that it interferes with itself

Ooer! So it's not just a male thing then, or are electrons male?!

[themos]

you need to believe in a world where the classical equations don't hold.

There is no problem in that. All photons are virtual until a measurement-magic (quantum TM) takes place and then we have to make initial and final states be classical.

[Tiny]

I like to think that just next to me in a parallel universe another me is inputting this too. And there are plenty more out there too! ......

[EA2007]

I like to think that just next to me in a parallel universe another me is inputting this too. And there are plenty more out there too! ......

Hello my other self.....your probably writing the same thing as me this very moment OR you have realised that you are way cooler and are currently sat in some million dollar mansion enjoying the company of some fine young ladies...damn!

[narrowbandpaul]

aaarrrggghhhhh quantum mechanics........

i am being bombarded with QM at uni....fortunately its really cool...

The double slit with single electron/photons is pretty wierd...

[ChrisEdu]

I like to think that just next to me in a parallel universe another me is inputting this too. And there are plenty more out there too! ......

Hello my other self.....your probably writing the same thing as me this very moment OR you have realised that you are way cooler and are currently sat in some million dollar mansion enjoying the company of some fine young ladies...damn!

Plus there's the idea that an infinite number of possibilities from your life are all played out in parallel universes. Right now, I must be murdering my boss and sleeping with Kylie!

[ChrisEdu]

Weirdly enough, as I was writing my previous post, I happened to have a post open, on a completely different forum (about watches), that happened to mention parallel universes! Spooky! :? :shock: