Exotic Matter

[freyar]

They don't.

Well, to first-order approximation they don't - they are electromagnetic waves, and so they like to interact with electric charges, even when they themselves are neutral. There are some more rare effects that make for a non-zero probability of it happening.

But either way - when a particle-antiparticle pair interact, they turn to energy, which likely comes out as photons that had energy that totaled up what went into the particle-antiparticle pair.

When the photon-antiphoton pair interact, they turn to energy, which likely comes out as... photons. Photons with the same total energy as what went in. So... they'd look *exactly the same*. How would you really know if they'd interacted or not?

Freyar will likely grump at me now for being a tad inexact. I'll deal

Nah, this is all good. As usual, I can elaborate, though. There are a couple of rare types of events Umbran is talking about.

One is that two photons can interact and turn into an electron/anti-electron pair if they have enough energy to do so. If you had an easy way to make very energetic photons, this would happen as much as electron/anti-electron annihilation. People usually call it pair creation from the electron's point of view. These events are rare not because they are unlikely to happen given the right circumstances but because we don't really have too many ways to make lots of high energy photons, at least not without using some kind of matter/anti-matter annihilation to start with (so the right circumstances are rare).

The other type of rare event is photons actually bouncing off of each other. At a microscopic level, the photons don't interact with each other but with quantum "virtual" electrons. This is a rare event just because, even when photons get close to each other, they don't generally both interact with virtual electrons at the same time.

 

[tomBitonti]

The other type of rare event is photons actually bouncing off of each other. At a microscopic level, the photons don't interact with each other but with quantum "virtual" electrons. This is a rare event just because, even when photons get close to each other, they don't generally both interact with virtual electrons at the same time.

Can you expound on that? I've read (if memory serves me) of interaction of photons with virtual particles as a cause for "tired light" which is an alternate (but dis-proven) mechanism for photon red-shift. I've wondered why such interactions don't cause a lessening of the speed of light in a vacuum, based on the proportion of time the photon spends interacting with the virtual electron, or extra dispersal of a collection of photons which are initial in phase.

Thx!
TomB

 

[megamania]

Feel like this is an episode of Big Bang Theory and I'm Penny

 

[Scott DeWar]

Nah, this is all good. As usual, I can elaborate, though. There are a couple of rare types of events Umbran is talking about.

One is that two photons can interact and turn into an electron/anti-electron pair if they have enough energy to do so. If you had an easy way to make very energetic photons, this would happen as much as electron/anti-electron annihilation. People usually call it pair creation from the electron's point of view. These events are rare not because they are unlikely to happen given the right circumstances but because we don't really have too many ways to make lots of high energy photons, at least not without using some kind of matter/anti-matter annihilation to start with (so the right circumstances are rare).

The other type of rare event is photons actually bouncing off of each other. At a microscopic level, the photons don't interact with each other but with quantum "virtual" electrons. This is a rare event just because, even when photons get close to each other, they don't generally both interact with virtual electrons at the same time.

Can you expound on that? I've read (if memory serves me) of interaction of photons with virtual particles as a cause for "tired light" which is an alternate (but dis-proven) mechanism for photon red-shift. I've wondered why such interactions don't cause a lessening of the speed of light in a vacuum, based on the proportion of time the photon spends interacting with the virtual electron, or extra dispersal of a collection of photons which are initial in phase.

Thx!
TomB

is all of this still in theory or has it been actually observed and reproduced in a lab?

 

[Scott DeWar]

Feel like this is an episode of Big Bang Theory and I'm Penny

believe me, I know what you mean!

 

[Scott DeWar]

As for Hawking radiation - dude, you're talking about having a warp drive. A main deflector dish isn't far behind

and that device is handy for so many other uses!

 

[Umbran]

and that device is handy for so many other uses!

It slices! It dices! It vaporizes! Whitens sheets, freshens breath, and is guaranteed to be able to channel more energy than any other emitter on your starship!

If you order now, you get a free set of phaser banks!

Plus, as a special added bonus, a matched bat'leth and dk'tagh set, for all your kitchen needs!

 

[tomBitonti]

is all of this still in theory or has it been actually observed and reproduced in a lab?

The bit about "weak light" is a well disproven idea. Virtual particles are demonstrated by the Casimir effect (putting two plates very close to each other). That's based on a very thin understanding and reading. I defer to others for anything in more depth.

Thx!
TomB

 

[Scott DeWar]

It slices! It dices! It vaporizes! Whitens sheets, freshens breath, and is guaranteed to be able to channel more energy than any other emitter on your starship!

If you order now, you get a free set of phaser banks!

Plus, as a special added bonus, a matched bat'leth and dk'tagh set, for all your kitchen needs!

shut up and take my money!

 

[freyar]

Can you expound on that? I've read (if memory serves me) of interaction of photons with virtual particles as a cause for "tired light" which is an alternate (but dis-proven) mechanism for photon red-shift. I've wondered why such interactions don't cause a lessening of the speed of light in a vacuum, based on the proportion of time the photon spends interacting with the virtual electron, or extra dispersal of a collection of photons which are initial in phase.

You're right, this wouldn't lead to "tired light" or slow down the speed of light. Basically, as a single photon travels along, it constantly excites (and de-excites) virtual electrons but in such a way that the wave speed of light is unaffected (and specifically is still independent of frequency). The reason for this is that the interaction between the photon and the electrons still respects special relativity. What it does effect, however, is how strongly photons and electrons interact, in other words, the value of the electric charge. You might have heard something to the effect that an electron is surrounded by a cloud of virtual electrons & anti-electrons that collectively "screen" the electron's charge. A photon hitting an electron with more energy gets closer to the electron, so it is screened less and effectively sees a larger electron charge.

This same kind of effect means that two photons can also "hit" each other. Most of the time, two photons will just pass each other by, but sometimes they will excite the same virtual electrons and can both bounce off that virtual electron.

is all of this still in theory or has it been actually observed and reproduced in a lab?

I'm not an experimentalist, so I don't keep track of every result like this terribly carefully. The following is my understanding, but I might have missed something:

Two photons coming together and creating an electron/anti-electron pair has been observed in a lab starting in the late 1990s AFAIK. The caveat is that the only way we have to produce energetic enough photons on earth is in high energy collisions of other things, so the photons involved are themselves fairly virtual (it's worth mentioning that virtual is not a binary descriptor but a continuous thing --- every particle is in reality a little virtual). On the other hand, this process appears to happen fairly commonly in astrophysics since there are lots of things in space that create high energy photons.

I don't believe two photons bouncing off each other in the vacuum has been observed yet, and in fact the predicted rate for this to happen is below current experimental sensitivity --- if we'd seen it by now, it would mean there's something we don't understand going on.

But it's worth mentioning that both of these types of events are embedded and inevitable in the Standard Model of particle physics AND any way we might know how to modify particle physics consistent with things we've already measured. If they didn't happen, it would mean we'd literally have to scrap almost a century of particle physics theory which has been otherwise remarkably successful. What I'm trying to say is that there are different degrees of "still just in theory." There's stuff like this, which pretty much has to happen given what we know already; there is a concept like dark matter, which we don't know a lot about but can be extremely confident exists from what we know; there is something like string theory or another approach to quantum gravity, which we can't directly access experimentally for the time being but is a logical extension of what we know and have observed (and can be tested mathematically); and there is something like the exotic matter needed for wormholes and warp drives, which doesn't really naturally come up for any other reason and can easily violate basic physical principles if you're not really careful about it.