[NotanOriginalName]

What are the processes involved in creating mass from pure energy

[Tres Juicy]

NotanOriginalName, on 24 January 2012 - 04:27 PM, said:

What are the processes involved in creating mass from pure energy

Magic?

[timo]

The main problem with this question is that "pure energy" is a substance only known to science fiction authors and participants of internet forums, not to scientists. The most widely known process to convert kinetic energy into mass is shooting particles with high kinetic energy onto each other, creating new particles in the collision. Such machines are called "particle accelerator" or "colliders"; the machine most widely know these days probably is the "Large Hadron Collider" (LHC).

[md65536]

The following story suggests doing the same with light:

http://www.nytimes.c...-particles.html

More stuff related to the last link:
http://science.slash...intensity-limit



However, the first link involves colliding photons and electrons (and I haven't read the second).
So it still involves particles... not the "pure energy" I think you were thinking of?

I suppose there would be no way to collide two photon beams, would there? Pauli exclusion doesn't apply to bosons such as photons, only fermions. So it should be possible for multiple light beams of any intensity to pass through the same space without "turning into matter". Light cannot act as an observer; it cannot receive light, so I suppose there's no way for two light beams to interact?

Can a boson decay into a fermion by itself, or does it need to interact with another fermion?

Edit:
"Fermions are usually associated with matter, whereas bosons are generally force carrier particles" [http://en.wikipedia.org/wiki/Fermion], so I think boson to fermion decay is close to the idea of converting energy to mass... However I think that it's probably incorrect to describe it literally as such???

This post has been edited by md65536: 24 January 2012 - 06:47 PM

[swansont]

md65536, on 24 January 2012 - 06:29 PM, said:

Can a boson decay into a fermion by itself, or does it need to interact with another fermion?

It would have to decay into two fermions in order to conserve spin. Mesons do it all the time.

NotanOriginalName, on 24 January 2012 - 04:27 PM, said:

What are the processes involved in creating mass from pure energy

No such thing as pure energy, but a photon can turn into a particle/antiparticle pair if it has sufficient energy to convert to mass (e.g. 1.02MeV for an e-e+ pair) and is in the presence of some massive particle to allow conservation of momentum.

[timo]

md65536, on 24 January 2012 - 06:29 PM, said:

I suppose there would be no way to collide two photon beams, would there? Pauli exclusion doesn't apply to bosons such as photons, only fermions. So it should be possible for multiple light beams of any intensity to pass through the same space without "turning into matter".

I think your inherent assumption that the Pauli principle is (exclusively) responsible for the interaction between particles is rather dubious

[michel123456]

md65536, on 24 January 2012 - 06:29 PM, said:

(...)I suppose there would be no way to collide two photon beams, would there? Pauli exclusion doesn't apply to bosons such as photons, only fermions. So it should be possible for multiple light beams of any intensity to pass through the same space without "turning into matter". Light cannot act as an observer; it cannot receive light, so I suppose there's no way for two light beams to interact?
(...)

No interference ?

[md65536]

michel123456, on 24 January 2012 - 06:49 PM, said:

No interference ?

Alright fine I don't know what I'm talking about.

No collisions. I'm not sure if interference could be considered interaction. The wave function has interference but the photons haven't affected each other??? I'm not sure how to form this into a correct statement.

Two photons may interfere and interact differently with their target, but they haven't directly interacted with each other.

timo, on 24 January 2012 - 06:48 PM, said:

I think your inherent assumption that the Pauli principle is (exclusively) responsible for the interaction between particles is rather dubious

Alright fine I don't know what I'm talking about.

I should have said, there are no interaction or principle (such as example Pauli exclusion) that allows for photon-photon collisions. ??? That also doesn't sound like the right way to say it.

This post has been edited by md65536: 24 January 2012 - 07:13 PM

[timo]

You probably should have said "I've never seen light beams reacting with another. I also would not understand how that should be possible. Therefore, I believe that there is no photon-photon interaction". That would, I believe, describe your reasoning rather accurately. It also wouldn't be too stupid: Extrapolating from the known into the unknown is certainly better than completely wild-guessing. Of course, in this case it happens to be wrong (you linked an article talking about a photon-photon -> matter experiment yourself). But learning from mistakes is often the most effective way of learning (if the mistake is properly reflected upon).


For the sake of completeness, here's the paper that the NY-times (presumably) talks about:
Original publication on PRL: http://prl.aps.org/a.../v79/i9/p1626_1
Publically-available pdf: http://slac.stanford...ac-pub-7564.pdf

This post has been edited by timo: 24 January 2012 - 07:40 PM

[md65536]

timo, on 24 January 2012 - 07:18 PM, said:

You probably should have said "I've never seen light beams reacting with another. I also would not understand how that should be possible. Therefore, I believe that there is no photon-photon interaction". That would, I believe, describe your reasoning rather accurately. It also wouldn't be too stupid: Extrapolating from the known into the unknown is certainly better than completely wild-guessing. Of course, in this case it happens to be wrong (you linked an article talking about a photon-photon -> matter experiment yourself). But learning from mistakes is often the most effective way of learning (if the mistake is properly reflected upon).

I don't trust whomever it was who linked that article above.
The above article isn't an experiment, but it theorizes a maximum laser energy, based on real experiments involving photons and electrons (edit: this isn't true. I should have read my own link, which says that photon-photon interactions happened after the photon-electron collisions).
I didn't really think about it, but I realize now that it clashes with my understanding of light, which I now realize is based on some assumptions that might be dubious.

Would it be correct to say that
1. Photon-photon collision has never been experimentally confirmed
2. There is no accepted theory that says that it's impossible

So it may one day be determined that it is impossible (contrary to the predictions of the article I linked), or it may one day be experimentally observed (or neither)?


I was extrapolating from the known in order to confirm my assumptions. Maybe not "too stupid", but a careless mistake nonetheless. A crackpot mistake.

This post has been edited by md65536: 24 January 2012 - 08:34 PM

[michel123456]

I am with md65536 a 100%.
My intervention about interference was genuine, I don't try to show how smart I am: I truly don't understand.

This post has been edited by michel123456: 24 January 2012 - 07:48 PM

[timo]

md65536, on 24 January 2012 - 07:39 PM, said:

Would it be correct to say that
1. Photon-photon collision has never been experimentally confirmed
2. There is no accepted theory that says that it's impossible

1) No. I edited the article describing an experiment into my previous post (I have not checked the guys' experiments, of course - they merely measured what everyone, including me, would expect to happen, anyways).
2) No. As a matter of fact, in quantum electrodynamics I think it follows pretty straightforwardly that in the limit of very high energies (where the mass of the electron is small compared to the energies) the probability for the process photon+photon -> electron+positron to happen is equal to that of the process electron+positron -> photon+photon.

Extrapolating from the known is not a crackpot mistake. Claiming that the extrapolation must be correct (even in the face of contradicting experimental results or contradicting widely accepted theory) is.

This post has been edited by timo: 24 January 2012 - 07:53 PM

[michel123456]

timo, on 24 January 2012 - 06:48 PM, said:

I think your inherent assumption that the Pauli principle is (exclusively) responsible for the interaction between particles is rather dubious

You should expand on this.

[md65536]

timo, on 24 January 2012 - 07:51 PM, said:

1) No. I edited the article describing an experiment into my previous post (I have not checked the guys' experiments, of course - they merely measured what everyone, including me, would expect to happen, anyways).
2) No. As a matter of fact, in quantum electrodynamics I think it follows pretty straightforwardly that in the limit of very high energies (where the mass of the electron is small compared to the energies) the probability for the process photon+photon -> electron+positron to happen is equal to that of the process electron+positron -> photon+photon.

Ah thanks. They do state that the observed positrons are interpreted to be the result of photon-photon interaction. However it would be stupid for me to assume it must be something else, without good reason. I guess I have to throw out my assumptions and re-evaluate my understanding.

So there is an example of light turning into mass, one interpretation of the original question in this thread.

[DrRocket]

NotanOriginalName, on 24 January 2012 - 04:27 PM, said:

What are the processes involved in creating mass from pure energy

http://en.wikipedia....-photon_physics