WTF is the speed of gravity

[Ethelred]

Originally posted by SwitchMoO


OK, I admit, regarding the actual event of creation, it isn't science. But then again, neither is the big-bacg theory, nor evolution.

Both are very scientific. Lots of evidence to support both. Megatons for evolution. Maybe gigatons as ALL life on Earth shows evolution in action.

That definition you quoted clearly does NOT fit Creationism which is the study of a book and the denial of any physical manifestions that show the errors in Creationism. Science is not about pounding gigantic round pegs into the tiny squares of Creationist religious beliefs. There simply is no physical reason for Creationist claims about evolution or the age of the Earth. Its ALL based on the Bible and the rest is a just a big sledgehammer trying to pound reality out of shape.

If you can't see it happening, it ain't science, and can actually never be proven. WE can look at the facts and derive a throey based upon them, but there is unfortunately no proof, nor will there ever be

I can't see an electron yet we have science covering the things. We CAN see evolution both in the fossil record and in the lab. Its a standard lie by Creationist organizations that there is no repeatable evidence of evolution. When confronted with lab experiments of course they go back on their own demands for repeatable evidence and claim it was just done in a lab so it has no meaning.

Too bad, I'd so love to prove creation, but all I can really do is give the facts and let you decide.

The facts are clear. Creationism is a belief that is in denial of reality. I have seen the Creationist stuff. It preposterous in many cases and in some recent more sophisticated stuff they have simply borrowed some real science used it at the start of their articles and then slide back to the preposterous stuff and pretend the two are related.

Well, about the time thing, Ok, you got me there. I forgot about that test.

However, when I mentioned 'c' differing, I meant that the speed of light was as much of a constant as the speed of time (? would that be 1 sec/sec? if time accelerated, it would be 1 sec/sec/sec, or 1 sec cubed )

The speed of light is the same no matter what speed you are going. If you were moving at 90 per cent of the the speed of light you would still measure it at about 300,000 KPS same as on Earth. The only question is whether the speed of light is the same now as it was in the distant past. We can see that for billions of years in the past its the same to limits of our ability to observe. There is a possibility that even farther back in time the speed may have been different.

[Rogan Josh]

Originally posted by Seeker
Also: Why are GUTs 'necessary'? What problems do they solve?

In some sense they aren't necessary. We could live in a world where the forces all had different explanations and had no link to each other. However, past experience show that this is not the case. Lots of experimental data point towards all the forces being different manifestations of the one force. Just like electricity an magnetism are different manifestatins of electromagnetism.

Why can't Einsteins 'geometric' description of gravity just stay seperate? Why do we need to connect gravity to the other forces? Maybe it isn't really a 'force' in the same sense and we're really dealing with a problem of definitions?

We know that the particles of nature obey the laws of quantum physics, but Einstein's gravity applied to quantum particles just doesn't work. It gives the wrong answers. Therefore we need a quantum theory of gravity to explain why and how these quantum particles feel the effects of gravity (and they clearly do). If Einstein's gravity were 100% right then out quantum theories would have to be wrong.

[Ethelred]

Thanks Rogan.

Originally posted by Rogan Josh
On the other hand, there are arguments of why supersymmetry should be weakly broken (or more technically 'softly' broken) called the 'hierarchy' problem. Basically, without the softly broken supersymmetry, the Higgs boson would naturaly have a mass around the Planck scale, making it so heavy that it would not interact strongly with the particles we know and love, thereby making them massless. Since everyone expects that we will find the Higgs boson, it looks likely that supersymmetry is only softly broken.

Everyone (well a lot of people anyway) expected to show that Universe is EXACTLY on the cusp of being closed at one point which now looks wrong. I will keep that in mind regarding the Higgs boson.

There are also plans (though no funding yet) to build an e+e- collider in Hamburg (called TESLA) which would give precise measurements of the supersymmertic partner particle's propeties when they are found. (I was one of the authors of the Technical Design Report submitted to the German government.)

Good luck with the funding. That sort of is just slightly expensive.

Whats the advantage of that type of collider over a proton-antiproton colider where there isn't as much of a loss of energy to synchrotron radiation?

[Rogan Josh]

Originally posted by Ethelred
Whats the advantage of that type of collider over a proton-antiproton colider where there isn't as much of a loss of energy to synchrotron radiation?

You are right about the synchrotron radiation. So much so, that an e+e- circular collider is infeasilbe for really high energies - you just lose too much energy to the synchrotron radiation. TESLA is to be a linear accelerator (like the one at SLAC), which accelerates the electrons and positrons all in one go up to the required energy (although it would have a synchrotron injector).

Hardron colliders like the LHC (which will be a proton-proton collider incidentally) are just too imprecise. The problem is that protons are not fundamental particles. The energies we want to probe are now high enough that we are really colliding the quarks (or rather for the LHC the gluons) inside the proton. But since we only know the energy of the proton and not the energies of the quarks and gluons inside the proton, it is very hard to do experimental tests with any accuracy. Basically we don't know the details of the initial collision we are investigating.

You are also right though that it is still much easier to obtain high energies with a hadron collider, so the LHC will probe much higher energies that TESLA (about 20 times higher). If one is not so interested in the details then hadron colliders are perfect because there is enough energy to create very massive particles. But if you want to precisely measure the properties of these particles you need a really clean collider like an e+e- machine.

For this reason, the LHC is sometimes called a 'discovery' collider, while TESLA is a 'precision' collider.

Incidentally, there is research being done on muon colliders. Muons are like electrons but much heavier, so they could be accelerated in a synchrotron to give a very high energy, but very precise collider (since they are fundamental particles). This is still 20 years away though.

As for the funding of TESLA, the main problem is that it is really too big for one country to build on its own - we really need a collaboration encompasing the entire world. While we are now reasonably united in areas (Europe, America and Asia), getting these areas together (funding wise) is difficult. We nearly had a deal sorted out last summer where the European technology (which is more advanced) would be used to build a collider in the US (so that not all the important colliders would be in Europe). But then September 11 hit and the funding disappeared...

[Ethelred]

Originally posted by Rogan Josh


You are right about the synchrotron radiation. So much so, that an e+e- circular collider is infeasilbe for really high energies - you just lose too much energy to the synchrotron radiation. TESLA is to be a linear accelerator (like the one at SLAC), which accelerates the electrons and positrons all in one go up to the required energy (although it would have a synchrotron injector).

OK that makes sense. SLAC is or originly was two miles long. I have vague memories of it when it was new and it was built to avoid synchrotron radiation that was becoming a real problem in the cyclotrons.

Hardron colliders like the LHC (which will be a proton-proton collider incidentally) are just too imprecise. The problem is that protons are not fundamental particles. The energies we want to probe are now high enough that we are really colliding the quarks (or rather for the LHC the gluons) inside the proton. But since we only know the energy of the proton and not the energies of the quarks and gluons inside the proton, it is very hard to do experimental tests with any accuracy. Basically we don't know the details of the initial collision we are investigating.

OK that makes sense also. The collisions will be a lot less messy with leptons.

Incidentally, there is research being done on muon colliders. Muons are like electrons but much heavier, so they could be accelerated in a synchrotron to give a very high energy, but very precise collider (since they are fundamental particles). This is still 20 years away though.

Muons are the second lepton aren't they the one in the middle on weight and lifespan or is that the Meson? Someone at the University of Utah (actually one of the guys on the fringe of the cold fusion hooplah) did experiments with heavy leptons for fusion. He was trying to make a hydrogen atoms with a Meson? Muon? instead of an electron so the atoms would be smaller and he would get a denser plasma.

Ahh found a page on leptons. I can never get names straight. I was thinking about Muons with that low temperature fusion experiment. Low not cold.

I see that the Russians are experimenting with that.

http://www.inr.ac.ru/INR/MMF.html

I see now that I was mixing up apples and oranges. Or rather Mesons and Leptons.

http://www.herts.ac.uk/astro_ub/a10_ub.html

Mesons seem a bit strange, even if they get down---

and of course anti-down. At the same very short time.

As for the funding of TESLA, the main problem is that it is really too big for one country to build on its own - we really need a collaboration encompasing the entire world. While we are now reasonably united in areas (Europe, America and Asia), getting these areas together (funding wise) is difficult. We nearly had a deal sorted out last summer where the European technology (which is more advanced) would be used to build a collider in the US (so that not all the important colliders would be in Europe). But then September 11 hit and the funding disappeared...

Well the funding for the Super Conducting Super Collider disapeared after the Feds bought the land and dug at least part of the tunnel. Don't expect much out the US for that kind of funding while Bush is in office. After all, things must be done by the private sector if they are really worth doing they should be able to make a profit. Especially in Texas. I don't think September 11 had a heck of lot to do with any reasearch funding costs. Team Texas prefers to give Federal money to Enron and other 'profit' producers.

[IoT]

Would you expect to get a high enough flux of muon - anti muons in order to perform these experiments? I assume the plan would be to run experiments for several months/years in order to get statistically significant sample size.

[Rogan Josh]

Yes, muons are from the second generation of leptons - so basically just heavy electrons. Mesons are not fundamental particles, but are quark-antiquark bound states. The confusion springs from the first experiment which saw the muon in Rome in '45 (I think). They thought it was a meson, so they called it the mu meson. Unfortunately some people still call it that even although it isn't a meson.

The problem with the muon collider is, as IoT pointed out, it is difficult to get good luminosity, due to 2 effects. Firstly, they are difficult to make and secondly (and more importantly) and the muon has a very short lifetime. Fortunately, relativistic time dilation means that they live longer the faster they are moving. Hopefully they will then be good for very very high energies, as long as we can pump enough energy into them quickly enough.....

...I wouldn't hold my breath though.

If you are interested in TESLA take a look here. The most interesting part of the TDR for non experts is part I - the executive summary.

[Ned]

Re: Ned the Physicisisisisist

Originally posted by Frogger
I'm going to assume that you are talking about the apparently obvious conclusion that the time of propagation of graivty from source to object would cause an aberration in the force exerted on the object, giving it a transverse acceleration dependent on v/c.

Nothing could be farther from the truth. The author simply "forgot" that Newtonian gravitation is wrong, and hand-inserting a time-delay doesn't make it any more right.

If you know GR, I can show that the leading-order term v/c disappears (and so do all other terms up to (v/c)^5). This makes the grav. radiation effect a quadrupole term. In other words, not very important. This is one of the fundamental topics covered in any intro GR course.

Neglible? OK.

Then, if you could, explain how does gravity traverses an event horizon?

[Ethelred]

The mass is still there. From what I have read any NEW mass that a Black Hole gathers in never actually enters the Black Hole due to gravitational time dialation. It piles up at the Event Horizon. This may apply to much of the mass that goes into forming the Black Hole initialy as well because most of it starts on the outside of the Event Horizon.

The question you ask doesn't apply to General Relativty as in that theory gravity is the warping of space itself. Its an interesting questing for Quantum Gravity.

The guys question about how matter falls in a gravity field from a stopped position shows the lack of understanding on his part. The question can only arise with a point mass. Any real mass has volume (except a naked singularity should there be any) and therefor is subject to a gravity GRADIENT. The mass being dropped is subjected to more warping in the volume closer to the larger mass than the opposite side of the object. Similar to a lighter than air balloon. Those don't rise simply because they are lighter. They rise because there is a pressure differential between the top and bottom of the balloon that is greater than the the weight of the balloon. Same for boats.

[Ned]

Ethelred, Then, as I understand what you are saying, in GR, gravity has no speed - it is not a wave that propagates.

[KrazyHorse]

Originally posted by Seeker
Why can't Einsteins 'geometric' description of gravity just stay seperate? Why do we need to connect gravity to the other forces? Maybe it isn't really a 'force' in the same sense and we're really dealing with a problem of definitions?

Maybe. That's my pet theory. However, QFT and GR aren't compatible...

[KrazyHorse]

Originally posted by Ethelred


Beginner? That stuff is from the Max Planc Institute. Next you will be calling the Princeton Advanced Studies Institute a place for the moderatly inteligent.

I was going to copy part of it and replace all but the most comprehensible parts with BLAH BLAH Einstein BLAH but half of it refused to even show when I pasted it into the reply box. Even Apolyton was to stunned by the equations to allow them.

Do you understand that stuff Frogger? I thought that kind of stuff was post-graduate.

I don't have a clue what tensors are except for being a part of mathematics that Einstein adapted for his use and they have "``effective'' stress-energy pseudotensor" .

PSEUDOTENSORS?

That stuff was being covered in the last 2 weeks of my intro to GR class. It didn't seem that bad. Then again, I already had a differential geometry and 2 Geo/Top courses behind me...

Pseudotensors. Looks like a tensor, fails to transform as one?

[KrazyHorse]

Re: Re: Ned the Physicisisisisist

Originally posted by Ned


Neglible? OK.

Then, if you could, explain how does gravity traverses an event horizon?

?

1) GR doesn't care about the event horizon. You can show it's there and you can perform energy calculations that show its effects on photons etc. using GR, though...

2) That has nothing to do with quadrupole radiation

[KrazyHorse]

Originally posted by Ned
Ethelred, Then, as I understand what you are saying, in GR, gravity has no speed - it is not a wave that propagates.

Yes it is, depending on how you want to look at it. It affects all points in space at a time such that the dot product of their 4-vector displacement from source is 0. In other words, in a 3-D with fixed time view, it propagates at the speed of light.

[KrazyHorse]

Ned, are you going to admit that an argument based on hand-inserting a time-delay into a thory we know is wrong in unlikely to give the correct answer?