Ask any question you want about Physics

originally posted by: IAmTheRumble
Let me ask a short question that isn't so simple, is it possible that Einstein's theories could be incorrect? Or is this totally out of the question?

originally posted by: dragonridr
Simple answer yes we continually try to disprove it. Have we no so far his theory has held up to everything we have thrown at it. Is it the correct answer again unlikely but what ever that answer is will incorporate relativity.

Einstein often spoke of Newtonian mechanics being correct in the "limiting case" of general relativity, which means Newton's theory appears to be right under many conditions, but not all.

The video I posted a few posts back suggests that general relativity might meet a similar fate, and might be determined to be right under many conditions, but not all. So whatever new theory replaces general relativity will need to show why it appears to be right in the "limiting case" just as Einstein showed Newtons' theories were right in the "limiting case".

a reply to: Arbitrageur

Technically speaking, you are always seeing the past in any mirror, from your washroom to your car. Not far enough to make a difference, but the past nonetheless.

originally posted by: pfishy
a reply to: Arbitrageur

Technically speaking, you are always seeing the past in any mirror, from your washroom to your car. Not far enough to make a difference, but the past nonetheless.

Talk about fishing. Hahahaha

originally posted by: KrzYma
a reply to: Arbitrageur

haha... nice you frog !
you must be one if you see photons as you said.
*kidding

so I assume you telepathically communicated with a frog and it told you that ??

reincarnation ?? is this scientific "truth" like a black hole ??

Photons do exist... spent my PhD doing work characterizing photon counters.
Here is the catalogue www.hamamatsu.com...

Hamamtasu create other devices for photon counting, which are based entirely on the photo-electric effect. These devices are capable of observing single photons of light.

Though not my own paper, or thesis (again not wanting to openly and clearly identify myself on a mostly anonymous forum which might result in no so savoury things) here is a nice paper you can read about these devices and what single photons do to them
arxiv.org...

So, we can create devices that observe, very clearly, single photons... so why deny they exist?

originally posted by: bhaal
My question is this why is our known universe mostly matter, what happened to all the anti-matter.

This question is based on the assumption that at the start of the universe matter/anti-matter ratio was 50/50.

As Arbitrageur already said, it is an unsolved problem, but it is not a problem that we have no idea about. Only that the current observations/parameter space, make it difficult to solve.

The solution to the problem would be in the sector of CP violation. CP is charge parity, which is essensially the transform that describes particles and their relation to anti-particles. CP gives us a way of testing if interactions occur at different rates or probabilities between particles and anti-particles. If they do, it would mean that theoretically you can create anti-particles and particles in equal amounts allow them to decay and interact and be left with stuff left over at the end.

Thus far the quark sector doesn't appear to give us strong enough CP violation to result in what we see today. So we look at the lepton sector, namely neutrinos. This is a big part of study right this moment, with high energy neutrino beams being used to compare neutrino interactions, to their corresponding anti-neutrino interactions. CP violation in this sector has been shown to be possible, this is wrapped up in complicated oscillation physics.

Neutrino oscillation is an interesting quantum phenomenon that occurs over huge distances (completely unlike all quantum mechanical things that appear to only cover the smallest of distances. Here one flavour of neutrino (say an electron neutrino) may be produce, in say... the sun.. and because it has mass, it is possible in the lepton sector that mass and flavour eigen states do not transform over physical distance at the same rate. Thus its possible to create a electron neutrino, and then observe a muon or tau neutrino. Now the mathematics for this is quite complicated. BUT it predicts that there is a CP violating term within the formulation. What this means is that, if the amplitude of all other terms connected to the CP violating term are non-zero, then CP violation might be observable in the neutrino sector.

There are many theorists out there that claim to be able to do it, with neutrino sector CP violation, and quite easily get the matter/anti-matter asymmetry required. Spoke to a very wonderful theorist after a conference talk about it, believe it was Sacha Davidson, at Durham university at the time... not sure if she is still there anymore. Anyway, thats the current understanding, and thus far, we have tentative evidence for CP vilation, but no discovery yet

a reply to: ErosA433
Thanks for the much more thorough answer to the question.

a reply to: ErosA433

Thanks for the, albeit necessarily vague, information on your background. And also the links. I have been generally hazy on the arguments for the exact nature of the photon beyond just 'quantized light energy' myself. I have often taken the argument that it is a wave, until forced to collapse via interaction. Observed or not. Because the absorption and re-emitting property of the matter it encounters require a point particle of some sort. But the links you posted, while admittedly somewhat over my ability to truly process, still had enough content which I could grasp to further my understanding.

Ok, here's another question. Of course, I know they are extremely theoretical, but the nature of tachyons has always puzzled me. They would have to gain near-infinite amounts of energy to 'slow' (from our relativistic perspective) to C. So, what would their resting energy velocity be? Like, say, comparable to photons. And if they did exist, would they not just be particles of the dual-universe timeline which predicts that two universes sprang from our big bang/bounce, with one running in what we would perceive to be reverse time?

originally posted by: pfishy
Ok, here's another question. Of course, I know they are extremely theoretical, but the nature of tachyons has always puzzled me. They would have to gain near-infinite amounts of energy to 'slow' (from our relativistic perspective) to C. So, what would their resting energy velocity be? Like, say, comparable to photons. And if they did exist, would they not just be particles of the dual-universe timeline which predicts that two universes sprang from our big bang/bounce, with one running in what we would perceive to be reverse time?

The answer is no they wouldn't. Tachyons in string theory do not move faster then light. They would propagate at the speed of light just like a photon. The reason a lot of sights like to say they would is when we plug them into Einsteins equations they would have negative potential energy. Ok let's say we have two hills. Potential energy is considered to be how far up a hill I could get a ball to roll before it travels back in the other direction. If I add energy I can push it to the top of the next hill if I don't it will reverse direction and start traveling up the other hill until its potential is used then again reverse direction.

In strong theory well some strong theories not all. We can have a particle perfectly balanced on the top of our hill. There is no positive energy only negative. It can only fall down a hill. This has to do with ground States we could say a tachyon wouldn't have a ground state or lowest energy point.

Now universe wise this kind of instability is a very bad thing you could imagine why. This has the potential to keep going to lower and lower states to some eventual end if there is one. But let me back up a minute as to why tachyons would propagate at the speed of light. Here's a thought experiment. Let's say I have sticks with a ball on top perfectly balanced. If I touch it I release the potential energy it Toples over. Now let's put several in a row and connect them with springs. So we have rows and rows perfectly balanced with springs between them.

You could argue this was the state of the universe at the beginning huge amount of potential energy and nothing happening. But now we touch one this transfers to the next and the next as they seek there ground state. This interaction at most could occur at the speed of light which is instantaneous. It can never exceed instataneous. Because the interaction can't happen without time.

Now in string theory I would have to show you quite a few things to fully get you to understand like open and closed strings. And how open strings can be come closed strings or loops as you will. This is basically a graviton a closed string.

So ill close by saying no tacheons in any theory of strong that I have ever heard move faster then light they cant. It is easy to remove tachyons from string theory they aren't necessary. So the likely hood they exist isn't good. But if they do exist will find they are a gauge boson not all that different from a photon. And in fact could be looked at as another version of a photon. So now not being a strong theorist I'll say at this point it be better for you to ask questions to rap your head around this and I'll see if I have any lectures at work that can help.

a reply to: dragonridr

Hmm. Ok. I have not read much about them, as they are on the fringe end of hypothetical particles, but what little I have paid attention to was talking about their very nature being that of a FTL particle. I don't recall the sources (2 at most), so I can't say they were reputable, but if you can indeed link to some information about them it would be appreciated. Though, I do have to question your summation that they would be gravitons, if I understood you correctly. Yes, a closed string, and they would certainly have to be massless (if not negative mass, as I believe one article stated), but how do you estimate them to equate to a graviton? Are they also a spin 2 massless closed-string boson? If this is what you're saying, where do you derive that value from?
But, if I've misunderstood you, nevermind.

originally posted by: pfishy
a reply to: dragonridr

Hmm. Ok. I have not read much about them, as they are on the fringe end of hypothetical particles, but what little I have paid attention to was talking about their very nature being that of a FTL particle. I don't recall the sources (2 at most), so I can't say they were reputable, but if you can indeed link to some information about them it would be appreciated. Though, I do have to question your summation that they would be gravitons, if I understood you correctly. Yes, a closed string, and they would certainly have to be massless (if not negative mass, as I believe one article stated), but how do you estimate them to equate to a graviton? Are they also a spin 2 massless closed-string boson? If this is what you're saying, where do you derive that value from?
But, if I've misunderstood you, nevermind.

Any closed string in the universe by its very nature is a graviton. It's unavoidable in string theory. That's why the existence of them is shall we say unlikely. The reason fringe sights say they move faster then light is einsteines equation which isn't relative to string theory but should it be used. When you plug negative mass or energy into his equation you get something that propagated faster then light. But remember the equation isn't dealing with potential energy. Einsteins is dealing with existing energy on his equations and that's why they fail. Basically only silly people try to plug negative mass or energy into win stones equation it wasn't made for it since wins time said you can never have an omega over 1.

a reply to: dragonridr

Oh, I was unaware that the Graviton is the only closed string. I see where I misunderstood that, now.

Im wondering about the 4th dimension, how come the paradigm is changing from time to something else`?

a reply to: yulka

Could you be a bit more specific? Do you mean that it was classically considered to be time, but now is being looked at as possibly something else?

a reply to: pfishy

Yes

a reply to: yulka

Ok. I don't have an answer. I was just making sure that I understood your question, because it seems fascinating.

a reply to: pfishy

a reply to: yulka

Don't be disappointed. I'm not one of the big brains in this thread. I'm sure someone will come along to either answer your question or leave you scratching your head. I just comment within the admittedly limited confines of my understanding occasionally.

originally posted by: yulka
Im wondering about the 4th dimension, how come the paradigm is changing from time to something else`?

I'm not sure that it is, though I can see how one could get that impression from watching "Through the wormhole" where speculation and hypotheses almost come across as new science.

If you watch the video I posted on the previous page, it talks about some of the problems general relativity and quantum mechanics have in working together. We still don't have a solution to that problem but one idea is string theory with extra dimensions, though the dimensions would be very compact and not like the dimensions we normally think about.

Maybe some string theorists have a "changing paradigm" but I tend to view them as mathematicians and in fact some work in the math departments of their universities. There are numerous physicists who are still waiting for some evidence string theory can be confirmed by experiment before changing their paradigms. In fact you can find debates between physicists and string theorists, such as this debate between Lawrence Krauss and Brian Greene:

Brian Greene and Lawrence Krauss - The great String Theory debate


At about 7:30 Brian Greene discusses the way string theory might help get general relativity and quantum mechanics working together, but he admits it's just an idea. So maybe watch 1 minute from 7:30 to 8:30 if you can, or watch more if you want more insights into the debate about string "theory" which is a bit of a misnomer. Some have suggested it should be called "string hypothesis"; I agree.

originally posted by: ErosA433

originally posted by: KrzYma
a reply to: Arbitrageur

haha... nice you frog !
you must be one if you see photons as you said.
*kidding

so I assume you telepathically communicated with a frog and it told you that ??

reincarnation ?? is this scientific "truth" like a black hole ??

Photons do exist... spent my PhD doing work characterizing photon counters.
Here is the catalogue www.hamamatsu.com...

I somewhat disagree. Have you seen photons in mid flight? Or just at the moment of emission and absorption?

thanks

ps. and what keeps photon, according to you, as a particle in one piece while it travels through space? By all means photon should dissipate into energy pool surrounding eventually as soon as it was emitted. What you see at the detector is fore front of emission wave hits the senor, what it registers is sample of that wave with all its characteristics.

otherwise explain please what is keeping photon as a distinct entity while it travels in space?

thank you

cheers))