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ATLAS sees first direct evidence of light-by-light scattering at high energy

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Re: ATLAS sees first direct evidence of light-by-light scattering at high energy

#31

Post by soVeryTired »

ekimekim wrote: post #29
yohann305 wrote: post #25

Anyone else here is having a hard time seeing what could be applied usage of light-by-light scattering? (ie new computers? new internet? new telescopes?) Can someone here give us some insights?

Currently, very little. According to the article, you need crazy particle-accelerator-levels of energy to have them happen at all. However, by studying and understanding such events, we can test and improve our theories of physics, which may lead to breakthroughs in technology we can only dream of. For example, general relativity would have been considered completely useless knowledge for any practical purpose when i…

I've heard people make the argument about GR being essential to the GPS system before, but the skeptic in me has doubts. I don't deny that it's useful to have a correction derived from relativity, but is it really as essential as people make it out to be? If we hadn't known about GR when we built the GPS system, wouldn't we have realised there was an unexpected drift in the clocks and found a way to recalibrate them periodically?

Re: ATLAS sees first direct evidence of light-by-light scattering at high energy

#32

Post by mabbo »

yohann305 wrote: post #25

Anyone else here is having a hard time seeing what could be applied usage of light-by-light scattering? (ie new computers? new internet? new telescopes?) Can someone here give us some insights?

The bleeding edge of physics and other science and math if often just a lottery. You research something, show that it's probably correct even if it's not practical in any way, and then years later someone says "you know, if we just applied..."

Modern cryptography would be impossible without number theory, yet all the breakthroughs that made it possible took place decades and centuries beforehand. All they needed was "with a computer" for it to become vital to our everyday lives.

Re: ATLAS sees first direct evidence of light-by-light scattering at high energy

#33

Post by beojan »

soVeryTired wrote: post #31
ekimekim wrote: post #29

Earlier quoted context omitted.

Currently, very little. According to the article, you need crazy particle-accelerator-levels of energy to have them happen at all. However, by studying and understanding such events, we can test and improve our theories of physics, which may lead to breakthroughs in technology we can only dream of. For example, general relativity would have been considered completely useless knowledge for any practical purpose when i…

I've heard people make the argument about GR being essential to the GPS system before, but the skeptic in me has doubts. I don't deny that it's useful to have a correction derived from relativity, but is it really as essential as people make it out to be? If we hadn't known about GR when we built the GPS system, wouldn't we have realised there was an unexpected drift in the clocks and found a way to recalibrate them…

> If we hadn't known about GR when we built the GPS system, wouldn't we have realised there was an unexpected drift in the clocks and found a way to recalibrate them periodically?

And hence have discovered GR in the process. Alternatively (and more likely) we would have decided the idea simply doesn't work.

Re: ATLAS sees first direct evidence of light-by-light scattering at high energy

#34

Post by Coding_Cat »

madaxe_again wrote: post #27
Coding_Cat wrote: post #22

Earlier quoted context omitted.

I doubt that is the case. As the article nores photon-photon scattering has been a predicted for a long time by QED. Even if it wasn't detected before it's impact on redshift could be calculated. If you look at the abstract on the linked nature page the interaction has a cross-section of 70nb, which corresponds to a circle of radius 1.5e-9 nanometer[1]. It might occur a few times near a supernova or the swirl of a an…

but I doubt it has a meaningful effect in deep-space. Don't underestimate how often unlikely events can happen in a big enough space... As to photon-photon scattering, I might be wrong, but I don't believe it's considered in any models for expansion - similarly, if you do build light momentum transfer into your model, then expansion goes away - but because we "know" expansion to be true, those results aren't consider…

>Don't underestimate how often unlikely events can happen in a big enough space...

That's true but the density of photons (from a given source) also drops of cubically as you move away from the source.

> imilarly, if you do build light momentum transfer into your model, then expansion goes away

I'm not really a cosmologist, but I know some physics (QFT in particular). If you have a derivation for a formula giving the impact of YY-scattering on redshift I'd love to read it.

> but because we "know" expansion to be true, those results aren't considered or published.

We know redshift to be true, and we have evidence for expansion based on measurements. Something that simply denies this will have a hard time being published. A theory that explains those findings without using expansion however would certainly make waves.

As and aside, since the cross-section of photon-photon scattering is energy dependent (and, as far as I can tell cosmological redshift is not), wouldn't that be a way to distinguish them? Scattering should occur more often at higher energies meaning that after a significant amount of scattering a bundle's spectrum should clump up more into the red.

Re: ATLAS sees first direct evidence of light-by-light scattering at high energy

#35

Post by dragonwriter »

soVeryTired wrote: post #31
ekimekim wrote: post #29

Earlier quoted context omitted.

Currently, very little. According to the article, you need crazy particle-accelerator-levels of energy to have them happen at all. However, by studying and understanding such events, we can test and improve our theories of physics, which may lead to breakthroughs in technology we can only dream of. For example, general relativity would have been considered completely useless knowledge for any practical purpose when i…

I've heard people make the argument about GR being essential to the GPS system before, but the skeptic in me has doubts. I don't deny that it's useful to have a correction derived from relativity, but is it really as essential as people make it out to be? If we hadn't known about GR when we built the GPS system, wouldn't we have realised there was an unexpected drift in the clocks and found a way to recalibrate them…

If you don't have GR, you aren't going to do gravity maps (because you have no reason to think you need them).

Without that, you don't have much opportunity to discover the basis of the correction (which, as others have pointed out, is just discovering GR, anyway.)

Re: ATLAS sees first direct evidence of light-by-light scattering at high energy

#36

Post by jerf »

beojan wrote: post #33
soVeryTired wrote: post #31

Earlier quoted context omitted.

I've heard people make the argument about GR being essential to the GPS system before, but the skeptic in me has doubts. I don't deny that it's useful to have a correction derived from relativity, but is it really as essential as people make it out to be? If we hadn't known about GR when we built the GPS system, wouldn't we have realised there was an unexpected drift in the clocks and found a way to recalibrate them…

> If we hadn't known about GR when we built the GPS system, wouldn't we have realised there was an unexpected drift in the clocks and found a way to recalibrate them periodically? And hence have discovered GR in the process. Alternatively (and more likely) we would have decided the idea simply doesn't work.

"Alternatively (and more likely) we would have decided the idea simply doesn't work."

No, we would just keep beating on it until it works. It's a myth that science always precedes engineering. It's a very regular drift, and worst case scenario, if they just couldn't work it out, they'd build several ground stations in known locations, derive corrections as those drift, and upload corrections into the system periodically. (Similar things are done today: https://en.wikipedia.org/wiki/Differential_GPS )

Even with the science that we have, there's still fudge factors and empirically-determined values we have to use anyhow, because the Earth is not homogeneous and we have to take its slightly-lumpy gravity field as a given, not something we can "scientifically" determine. (Of course we "use science" to determine the lumps, but the lumps themselves are simply a given.)

Re: ATLAS sees first direct evidence of light-by-light scattering at high energy

#37

Post by jerf »

chi17 wrote: post #9
etatoby wrote: post #7

One step closer to holograms.

Could you explain? Also, do you not think that current implementations that use eye tracking are not real holograms? What's to say that holograms similar to those of Star Wars could not be produced by inspecting the environment and automatically determining where people's head and eyes are, e.g. via a combination of technologies similar to the following: Eye-tracking holographic table requiring 3D glasses: http://www…

This is closer: http://www.pocket-lint.com/news/131622-holograms-are-finally...

Star Wars-style holograms implies that I don't need additional equipment or special angles or anything, just a (basically) magical "hologram" projector. As that link shows, it may not be entirely out of the question, but, well... I'm not sure I want to be in the same room as one of those.

Re: ATLAS sees first direct evidence of light-by-light scattering at high energy

#38

Post by baq »

pif wrote: post #30
nimish wrote: post #20

Earlier quoted context omitted.

Photons carry no charge, so normally they don't interact with each other. However, at high enough energies they do. The explanation given by the best available theory is that there is enough energy that a virtual electron and virtual anti-electron form, and since those have charges, they interact, and from the outside it appears that the photons interacted. This is totally impossible in the classical view, but is fin…

High energies are not absolutely necessary. Couples of "virtual" particles can be created at any energy, it's just less likely for smaller energies. I think the real problem was the experimental set-up: particle accelerators use electric field to transfer energy to particles and magnetic field to control their trajectory and eventually to cause collisions, but all of this only works with charged particles. And photon…

> Couples of "virtual" particles can be created at any energy

doesn't the energy need to be at least the mass of the virtual particle?

Re: ATLAS sees first direct evidence of light-by-light scattering at high energy

#39

Post by renox »

yohann305 wrote: post #25

Anyone else here is having a hard time seeing what could be applied usage of light-by-light scattering? (ie new computers? new internet? new telescopes?) Can someone here give us some insights?

Finding new particles: https://arstechnica.com/science/2017/08/researchers-may-have...

Re: ATLAS sees first direct evidence of light-by-light scattering at high energy

#40

Post by triclops200 »

madaxe_again wrote: post #28
m1el wrote: post #24

Earlier quoted context omitted.

> I'm keeping my money on expansion and dark matter being hooey brought about by incomplete of incorrect understanding of light. That's a very interesting hypothesis. Unfortunately, it's easy to verify that photon-photon scattering doesn't explain the expansion of the universe. 1) photon-photon scattering is elastic, so no energy is lost, and no redshift is occuring 2) if it isn't elastic, the scattering is a random…

Those are all solid points, so I retract - but the momentum paradox bit stands! I wish I had someone else to chat physics with - isolation leads to screwy notions which can easily be quashed by the right counterpoints. Edit: a thought. Please (genuinely!) tell me where I'm wrong. As it's elastic, could we not end up with groups of lower energy photons with the same vector as an original high energy photon, which woul…

It looks like from what we know, 2 high energy (it's much less common with low energy) photons collide and change direction: from what I understand, they don't split into low energy photons. It'd be basically impossible for all the high energy photons to scatter directly away from earth (why would the earth be special?) leaving only low energy ones towards us.
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