41–50 of 82 posts
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?
Cryogenic freezing of magnets so that they would be useful as superconductors allowed people to create MRI.
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…
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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?
Earlier quoted context omitted.
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?
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> 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 periodica…
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I think at the moment they use a level 1 hardware trigger and a level 2 software trigger. ALICE is moving to a pure software trigger.
When I last participated to ATLAS, working in the Trigger & Data Acquisition group, ATLAS had 3 levels of trigger: the first was hardware, the others were software. Regarding the first level, software was not an option due to the extremely high bunch-crossing frequency (40 million times per second). The difference between the 2nd and 3rd levels consisted of data availability (region-of-interest only for 2nd, full det…
Can someone explain this in easier terms for a layman like myself?
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…
Not having charge doesn't imply they don't interact. They just don't through the electromagnetic force. Neutrons also have no charge but interact via the strong force, for example.
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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…
Neat-o. A little bit more info at https://en.wikipedia.org/wiki/Two-photon_physics . Basically two photons with enough energy to interact via virtual pairs created. It will be interesting to see the cross-section rates and maybe hopefully some new physics (as the wikipedia page weakly hints).
Or could it be that a photon bends space-time as though it had mass, and they simply follow the local curvature and it looks like scattering? Just speculating, because for some purposes photons act like a solid particle with their energy equivalent mass traveling at speed c.
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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.
Fascinating to wonder how modern physics community worldview would be different, if GR had gone [empirical anomaly -> new theory], and ended up in the same place rather than [thought experiment -> empirical proof]. (IAN a historian of physics - forgive me if I have that wrong.)
> Alternatively (and more likely) we would have decided the idea simply doesn't work.
I don't think that's true. Consider the Bell Labs guys who won the Nobel Price for Microwave Background Radiation, who were just trying to remove the noise their antenna was receiving.