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Re: Physics anyone?
Posted: Tue May 20, 2014 4:49 pm
by _ronzlo_
^ More importantly, just because this conversion (which has always been theoretically possible under gen. relativity) is finally close to happening in a lab setting doesn't necessarily mean that it's something that's, like, useful to do - enormous amounts of energy to create extremely basic matter just to show it can be done - unless it can yield some novel/useful kind of new matter.
Scientific equivalent of running up the down escalator in a way.
Also, it's not entirely right to say this has never been achieved in lab before:
NBC science wrote:
Update for 8 p.m. ET May 19: Any scientific claim that something physically possible has "never been done" will almost surely set off a debate, and that's the case for the light-to-matter trick. In an email, Bruce Schumm makes a strong case that it's been done before:
"I'm a physics professor at UC Santa Cruz and a longtime user of the facilities at the SLAC Linear Accelerator Center on the Stanford campus (where you may recall that quarks were discovered in the late 1960s). It is NOT true that the Breit-Wheeler process has never been discovered before. In fact, at this very moment I happen to be running a little experiment using the very same electron beam that a group headed by Adrian C. Melissinos of the University of Rochester used way back in 1997 to demonstrate this process. ... So while the scientists in the article may be making it much more copiously than in the past, they are not the first to produce matter by colliding beams of light!"
Schumm points to a New York Times article about the experiment, which was described in Physical Review Letters. The 1997 article in the Times said Melissinos and his colleagues "confirmed a longstanding prediction" by Breit and Wheeler about using light to create particles.
One caveat is that the SLAC experiment depended on a complicated interaction with a beam of high-energy electrons — and that's the thread on which Pike and his colleagues hang their claim for the novelty of the proposed photon-photon collider. Their paper in Nature Photonics even cites the earlier work, saying that such experiments don't qualify as pure photon-photon collisions because they "involve massive particles."
Re: Physics anyone?
Posted: Wed May 21, 2014 5:27 am
by Phigure
yeah also not only was it something predicted by relativity, you can argue that it was even more strongly supported by quantum electrodynamics which is literally the most accurate scientific work ever created (made predictions which were shown to be correct up to 10 decimal places!)
Re: Physics anyone?
Posted: Wed May 21, 2014 7:52 am
by titchbit
not quite sure what you're asking, but if you're asking if the elctromagnetic force or any force besides gravity can have a significant effect (except for very rare situations) on objects at far distances, i don't think that could happen, mainly because with gravity, everything so far as we know has a mass > 0 (ie a positive number). It's all > 0 so hypothetically the total mass of the universe could be infinity, which is positive. the em force can have values +1, 0 <1, so in a large body like a planet or sun, the net force is zero, so there's no acceleration or "pull".'''
pretty sure the same happens with the other 2 forces but they also act very week at long distances (1/r^2)
Re: Physics anyone?
Posted: Wed May 21, 2014 7:54 am
by Phigure
who are you responding to
Re: Physics anyone?
Posted: Wed May 21, 2014 7:57 am
by titchbit
fuck i can barely keep my eyes open im really messed up. i was responding to jesslem 2 pages ago lol wooooow
viewtopic.php?f=7&t=265855&start=340#p3622429
Re: Physics anyone?
Posted: Wed May 21, 2014 8:00 am
by rickyarbino
Have we not figured how to create energy from matter?
I assumed we had, and immediately thought of Cherenkov radiation, but then closer inspection lead me to find that at least that was because of KE. But I feel like I've discussed that at some point or another in class/with colleagues.
If it is the case, I'd have assumed that you could go both ways because of the energy mass equivalence. In any case, wouldn't it have been true because of the equivalence? I know you can say that's just treating nature as maths, but it works well enough in other cases, i. e. de Broglie wavelengths and so forth.
Re: Physics anyone?
Posted: Wed May 21, 2014 8:04 am
by Phigure
jesslem wrote:Have we not figured how to create energy from matter?
we have, nuclear fission is the obvious example. excess energy from breaking apart atoms is given off in the form of photons.
the significance of that paper isn't that theyve discovered they can turn light into matter, everyone knew it was possible and in fact we do it all the time in complicated experiments, it was just that they had come up with a process to do it more efficiently (in the sense that you could build what amounts to a photon-photon collider, like how we have electron-positron or proton-proton colliders)
Re: Physics anyone?
Posted: Wed May 21, 2014 8:25 am
by rickyarbino
But that's just energy from higher KE isn't it? Energetically unstable atoms trying to reach equilibrium. That's not matter becoming energy, but a chain of energetic events. Unless the electrons lose mass, but I'm pretty sure they don't.
Re: Physics anyone?
Posted: Wed May 21, 2014 8:40 am
by Phigure
come on man, in basically every physics text in the world, next to the part where they introduce e=mc^2, they have a picture of a mushroom cloud
forget electrons, fission is really just about the nucleus
it can either happen spontaneously in an unstable isotope (beta decay) or by bombardment. either way, the nucleus becomes unstable and breaks apart, leaving you with larger fragments (lets say we start with a uranium 235, we might end with two new nuclei of 95 and 137, or 92 and 140, etc), some free neutrons, and a bunch of gamma rays. if you were to take the mass before and then measure the mass of the fragments + free neutrons alone, you would have a few hundred eV worth of mass missing. those are the gamma rays (photons).
Re: Physics anyone?
Posted: Wed May 21, 2014 8:42 am
by rickyarbino
Hmm, guess I over thought that and forgot what it actually said
Edit.
Maybe I didn't really 'know' to begin with.
Re: Physics anyone?
Posted: Wed May 21, 2014 9:18 am
by rickyarbino
@ Dubu
I'm not too clear on the train of thought of the time, but I think that wasn't what I was asking. In any case, I don't think that would affect the interaction of positively and negatively charged particles, or rather their ability to interact at a distance.
Side note,
I think it's compatible with gravitational collapse.
Re: Physics anyone?
Posted: Wed May 21, 2014 4:40 pm
by titchbit
"I don't think that would affect the interaction of positively and negatively charged particles, or rather their ability to interact at a distance." --> what does that mean? can you be more specific?
you seemed to be asking if gravity could actually be the result of forces like "the sum of charges, for instance, of celestial bodies affecting the pulling (of each other?)".
for large objects the electromagnetic force is nullified because you got lots of +1s and -1s, but with gravity it's only +1s. so the electromagnetic force does not have an effect on long distances (usually - maybe in the case of certain exotic stars but idk), and can't be responsible for what we call 'gravity'.
Re: Physics anyone?
Posted: Wed May 21, 2014 4:46 pm
by nowaysj
Dude, magnetars.
Re: Physics anyone?
Posted: Thu May 22, 2014 2:38 pm
by rickyarbino
nowaysj wrote:Dude, magnetars.
Yeah, magnetars.
Re: Physics anyone?
Posted: Thu May 29, 2014 12:28 am
by _ronzlo_
Re: Physics anyone?
Posted: Thu May 29, 2014 12:37 am
by Muncey
Can someone with more knowledge than just watching youtube documentaries (thats my level) explain the legitimacy of supersymmetry? Is it actually a respected theory?
Finished my exams, gunna raid the library on random physics books I reckon.. delay looking for a job even longer.
Re: Physics anyone?
Posted: Thu May 29, 2014 12:38 am
by nowaysj
Y'all not talking about that GRB? Was it?
Re: Physics anyone?
Posted: Thu May 29, 2014 5:35 pm
by _ronzlo_
Muncey wrote:Can someone with more knowledge than just watching youtube documentaries (thats my level) explain the legitimacy of supersymmetry? Is it actually a respected theory?
Finished my exams, gunna raid the library on random physics books I reckon.. delay looking for a job even longer.
I'll let someone who really knows what they're talking about (cough... Phig) explain in detail, but as for its current standing: it's a theory that many want to be true because it explains some things so neatly and bridges quantum & classical models elegantly, but there's been no significant recent experimental support afaik. The Large Hadron Collider hasn't found anything, and in fact has found particles (heavy Bosons) that appear to contradict supersymmetry somewhat.
Good read here:
http://www.scientificamerican.com/artic ... etry-dead/
I like the multiverse anyway. Makes for better sci-fi.
Re: Physics anyone?
Posted: Mon Jun 02, 2014 9:32 pm
by Muncey
Nice one, that pretty much cleared up all I wanted to know. That article was really interesting too.
Re: Physics anyone?
Posted: Mon Jun 02, 2014 11:09 pm
by Phigure
still got my fingers crossed for a 100 tev collider some time in the 20-30 years so we can really either confirm or rule out supersymettry (among other things)