Theoretical Physics [OT thread]
 

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Darwin:
You can't accelarate a squirrel to the speed of light squared becuase matter cannot reach the speed of light and nothing can exhead it. In this case the speed of light is just being used as a number not as a speed. Why it works out to exactly the speed of light squared is one of those quantum physic things that I don't know.<HR></BLOCKQUOTE>

Well, we can't do this with current technology; there's some dissent on this matter in the physics community. I found an article not too long ago that mentioned an experiment where a particle was accelerated beyond the speed of light. HOWEVER (and this is a tricky point), scientists still believe INFORMATION cannot travel faster than light. So the particle can be accelerated and do damage, but it can't be used to provide FTL communication.

As for the speed of light being an important constant, it happens to be the speed of all electromagnetic waves; and, scientists believe, the speed of all forces in general. In other words, when a particle exerts a force on another particle, that force travels at 3x10^8 meters per second between the particles.

BTW - I'm posting this in a new thread, so we can stop cluttering up "Strategy" with "Theoretical Physics"...

Re: Theoretical Physics [OT thread]
 

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by DirectorTsaarx:
In other words, when a particle exerts a force on another particle, that force travels at 3x10^8 meters per second between the particles.

<HR></BLOCKQUOTE>

I don't know that that comment is entirely true. The equation for the gravitational force between two bodies F=G*M*M/R^2 seems to indicate the attraction is instantaneous. That makes sense to me, anyway.

Re: Theoretical Physics [OT thread]
 

Kimball -
You can't use Newtonian physics equations when describing relativistic situations (speed close to light speed, c). (Newton was a genius but one person can't discover everything.) You have to use general relativity equations, which are very complicated, involving stuff like tensors (which are like vectors but much worse). From those equations, it is believed that the force of gravity travels at the speed of light. The problem with observing this is that large hunks of matter tend to move at low speeds, so the gravitational field always seems to just "be there", unmoving, instantaneous. So you wind up looking for subtleties like the perihelion of Mercury being slightly different from that predicted by Newtonian theory. Big whoop. However, it is believed that one could detect gravity waves emitted from huge masses undergoing stupendous changes (for example, a supernova), and that these waves would move at the speed of light. There are several on-going experiments to detect gravity waves.

By the way, Einstein didn't get it totally right either. It is believed that general relativity is also incomplete, because it is incompatible with quantum mechanics. What I mean is, that when one attempts to "quantize" general relativity and to describe the gravitational force in terms of "gravitons" (analogous to photons), the whole thing falls apart. To his credit, Einstein knew this and it really bugged him. He spent the latter third of his life trying unsuccessfully to fix it (when he wasn't expressing his doubts about quantum mechanics).

Re: Theoretical Physics [OT thread]
 

Speaking of going faster than light, I read a very interesting book a LONG time ago that was based on the premise that our solar system had been traveling for eons in a region of space where c was reduced by 10 or a 100 compared to the rest of the universe. And then suddenly it came out, with the result that mental processes speeded up incredibly. Cows became sentient, monkeys became as smart as people used to be, average people became geniuses, and geniuses became frighteningly smart.

Re: Theoretical Physics [OT thread]
 

dmm

I see. I am engineer, not a physicist. I took just enough physics to be dangerous. http://www.shrapnelgames.com/ubb/images/icons/icon7.gif I don't disagree with what you said, but I don't know that I buy the "gravity waves" thing. I tend to believe the warped space theory of gravity that Einstein proposed. Looking at it that way, I think gravity would be instantaneous. Oh well.

Re: Theoretical Physics [OT thread]
 

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by DirectorTsaarx:
Well, we can't do this with current technology; there's some dissent on this matter in the physics community. I found an article not too long ago that mentioned an experiment where a particle was accelerated beyond the speed of light. HOWEVER (and this is a tricky point), scientists still believe INFORMATION cannot travel faster than light. So the particle can be accelerated and do damage, but it can't be used to provide FTL communication.

{snip}<HR></BLOCKQUOTE>

Actually, I think the experiment did not have a particle traveling FTL, but instead it was a wavefront which was "traveling" FTL (e.g. the peak or trough of a wave) which does not violate the ligtspeed "speed limit", there being a number of similar types of occurences which can travel FTL, but all are equally incapable of delivering information.

I think this article discusses the experiment you were talking about:
http://www.nytimes.com/library/natio...ics-light.html

--A Philistine

Re: Theoretical Physics [OT thread]
 

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by a philistine:
Actually, I think the experiment did not have a particle traveling FTL, but instead it was a wavefront which was "traveling" FTL (e.g. the peak or trough of a wave) which does not violate the ligtspeed "speed limit", there being a number of similar types of occurences which can travel FTL, but all are equally incapable of delivering information.

I think this article discusses the experiment you were talking about:
http://www.nytimes.com/library/natio...ics-light.html

--A Philistine
<HR></BLOCKQUOTE>

I couldn't get to the article (not willing to register with NY Times from my work computer), but you could be right about the wavefront moving FTL, not a particle. It's been a while since I read the article...

Re: Theoretical Physics [OT thread]
 

The Japanese discovered 2 years ago a particle that in it's natural state travels faster then the speed of light. Everything on the Earth is being bombard by this particle as it moves through space. I can't remember what they called it. I will try to locate the article. It has been a year since I read it.

Re: Theoretical Physics [OT thread]
 

The SF novel dmm is thinking of is Brain Wave, by Poul Anderson.


[This message has been edited by capnq (edited 01 March 2001).]

Re: Theoretical Physics [OT thread]
 

The information contained in a particle of any type includes its spin and mass. A particle can't travel faster than light. It can make light speed in the case of a photon, but travelling faster than light is against the rules.
Any subatomic particle is subject to uncertainty (it don't know where it is or it don't its vector). A wavefront of a particle would be smeared out in a probabilistic sense, so that the point at which the detector sees it is a critical probability threshhold. The uncertainty may allow the particle to appear to move faster than c, but it isn't. If you measured enough wavefronts and eliminated all that were slower than light speed you could come up with some evidence that your chosen wave was breaking the rules but on average everything stays below light speed.
This concludes my dogmatic and incomprehensible rant about stuff + things.

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<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Kimball:
...I don't know that I buy the "gravity waves" thing. I tend to believe the warped space theory of gravity that Einstein proposed.<HR></BLOCKQUOTE>
The gravity waves come straight from Einstein's theory. Think about it this way: suppose one member of a binary star system suddenly supernovas, taking out its partner. Locally, the warping of space changes "instantly", but far away no one knows yet that anything has happened. The light from the nova hasn't reached them. Everything looks normal. According to relativity, the warping of space far away will also remain unchanged at first. The change in the warping will propagate outward at the speed of light. That is what is meant by a gravity wave.

You might be thinking of gravitons, which at this point is more of a name than a serious theory. They are supposedly the particles that mediate the gravitational force, the quanta of gravity, analogous to photons. But no one has come up with a working theory of quantum gravity, so the jury is still out on whether or not gravitons actually exist.

Re: Theoretical Physics [OT thread]
 

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Dracus:
The Japanese discovered 2 years ago a particle that in it's natural state travels faster then the speed of light<HR></BLOCKQUOTE>
Maybe it travels faster than light in air? That's quite possible, and quite common. Neutrinos do that, and they constantly bombard us, and the Japanese have been working on some cool neutrino experiments for the Last few years. Maybe you're thinking of that? Particles are allowed to exceed the "local speed limit" which is always less than c. When they do, they give off forward-directed light known as Cerenkov radiation, which slows them down until they're below the local speed limit.

Re: Theoretical Physics [OT thread]
 

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Dracus:
The Japanese discovered 2 years ago a particle that in it's natural state travels faster then the speed of light. Everything on the Earth is being bombard by this particle as it moves through space. I can't remember what they called it. I will try to locate the article. It has been a year since I read it. <HR></BLOCKQUOTE>

"Tachyon" is a name which has been given to hypothetical particles which always travel faster than light. They can never travel slower than the speed of light.

I believe that there has been no "proof" of the existence of tachyons, although there has been a reported sighting in the 70's or 80's by someone studying cosmic rays that has never been reproduced, and there are some theories that tachyons are necessary to explain certain observable (or theoretically observable) conditions, which indirectly support their existence, but, AFAIK, nothing conclusive has yet been shown.

If you can find the article, please post a link.

--A Philistine

Re: Theoretical Physics [OT thread]
 

Ok, couple of things:

Gravity waves: physicists are spending large amounts of money on gravity infereometers to detect the presence of gravity waves. No-one has done so yet, but there is hope. Gravity wave detection is extremely difficult (if they even exist), because it is very hard to account for all disturbances possible. However, it is known that gravity, like other forces, travels at c (speed of light in a vacuum)

Tachyons: a postulated particle, never detected, whose important property is that it never goes slower than c.

FTL beams: Recently (Last summer), a group of physicists posted in Nature that they were able to fire a laser beam (laser beams are made up of photons, which are both wavelike and particlelike depending on what you are looking for) through a caesium filled chamber with a distance on the order of centimeters. The front wave of the beam contained all the information of the entire wave, and somehow caused an identical beam (although with much less amplitude) to be emitted from the far side of the chamber before the beam had fully entered the near side of the chamber. Measuring everything, these physicists were able to show the group velocity was much, much greater than c. Group veloccity is a hard thing to understand; it is very related to actual velocity, but is not the same. Take a couple of courses in Quantum Mechanics (an interesting subject in itself) and you might have a handle on group velocity. Anyways, these physicists believe that they did not violate relativity for various reasons. My best advice is to read up on this experiment yourself, for it is quite a well done experiment, and the results are still being interpreted.

The Japanese did the same thing, but with a much different wavelength of EM wave, and only exceeded c by 17% They are also not sure of what happened.

Kimball: I love it when engineers talk physics. It adds humor to my day... http://www.shrapnelgames.com/ubb/ima...ons/icon12.gif


Derek

Re: Theoretical Physics [OT thread]
 

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Derek:
Ok, couple of things:

Gravity waves: physicists are spending large amounts of money on gravity infereometers to detect the presence of gravity waves. No-one has done so yet, but there is hope. Gravity wave detection is extremely difficult (if they even exist), because it is very hard to account for all disturbances possible. However, it is known that gravity, like other forces, travels at c (speed of light in a vacuum)
{snip}Derek
<HR></BLOCKQUOTE>

Wasn't there observational (non-experimental) proof of gravity waves from rotating pulsars? I think it resulted in 1993 Physics Nobel?

--A Philistine

Re: Theoretical Physics [OT thread]
 

God, I've got to fresh up on my physics. Wow, yeah when I was talking about nothing going faster then the speed of light I was leaving out theorical particals for the sake of simplicity.

Isn't there something weird about the mass of Tachyons? Like having a zero mass? Or is that Neutrinoes?

Re: Theoretical Physics [OT thread]
 

Negative mass.

Or imaginary mass.

It depends on how you look at the equations.

By the way, by imaginary, I mean i, as it sqaure root of negative one style imaginary.


Derek

Physics is fun!

Re: Theoretical Physics [OT thread]
 

"Kimball: I love it when engineers talk physics. It adds humor to my day..."

Hmm, us engineers love it when scientists try to talk about theoretical impossibilities. Nothing has yet proven to be impossible. Flying? Nope, done that. Speed of sound? Nope, done that too. Flat Earth? Heh, yeah right. The moon? Yep, been there. Weightless environments near the surface of the Earth? Thats old news. Some day we will be saying the same thing about going faster than c.
Some things I would never hope for, though, are time travel (throws all conservation laws out the window, while creating fantastic paradoxes), getting 'out' of a black hole (you have a spec of dust that was your space ship, try getting that out of infinite gravitational force), and creating matter/energy (how do you create something from absolute nothing?).

Re: Theoretical Physics [OT thread]
 

Hate to tell you, but black holes do emit stuff and lose mass.

Hawking Radiation, where the black hole tends to absorb negative energy (and hence mass) from just outside the event horizon, and release positive energy(mass) to the environment.

Just one more thing to include in the list of not-impossible things.

Re: Theoretical Physics [OT thread]
 

Besides, a black hole is not an area of infinite gravity. It is an area where, after you go through the so-called 'event horizon', the escape velocity is greater than c, the speed of light.

Thats all.

Derek

Re: Theoretical Physics [OT thread]
 

It may have infinite density at the centre, but it only has finite mass.

If it had infinite mass, the entire universe would be inside the event horizon. (as soon as the gravity's effect spread out)


------------
PS. as for the 'weightless environments near earth' Might you be referring to the Vomit Comet, or something more dramatic that I can't remember?

[This message has been edited by suicide_junkie (edited 01 March 2001).]

Re: Theoretical Physics [OT thread]
 

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by suicide_junkie:
as for the 'weightless environments near earth' Might you be referring to the Vomit Comet, or something more dramatic that I can't remember?<HR></BLOCKQUOTE>
He might be referring to the demos where they used REALLY strong magnets to levitate little frogs. The upward force was due to the magnetic field causing the spins of all the froggie's atoms to line up, and they could tune it to exactly counteract the downward force from gravity. So, from the frog's point of view, it was weightless. They won't be using it to train astronauts anytime soon, though, because the region of uniform field is small compared to the size of the magnets.

Re: Theoretical Physics [OT thread]
 

Hey, thats a ready-made artificial gravity for spaceships!

Just scale it up ten times, and you've got a Grav-bed you can set to 1g for when you sleep in orbit. Build it with a superconductor, and it won't use up any electricity once its running, either.

You could also use it for when you're boosting to orbit, to cancel the 14g peak acceleration.

With a nuclear/antimatter fuelled engine, you could run continuously at high g's without crushing your crew.

Heck, maybe thats what SE4 races use when they go from a tiny moon, to a huge Rock world.

Re: Theoretical Physics [OT thread]
 

Hawking radiation is a theory, and not a very developed one from what I know. Actually all this stuff is theory, but that is the title of the thread.
Yes, an escape velocity greater than c is one technical description of the area beyond a black hole, but the other part of it is a star that has collapsed to infinite density, creating a singularity, and that generates an infinite gravitational force on the 'surface' of the singularity since it is at a zero distance from the total mass of the star.
And yes, I was referring to the 'vomit comet'. Technically, the space shuttle and other spacecraft also qualify, because they are not in a real zero-g environment, but they are not that close to the ground.
I haven't heard the one about the magnets, but that is interesting.

Re: Theoretical Physics [OT thread]
 

I guess that depends on what you consider "inside" a black hole.

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>(you have a spec of dust that was your space ship, try getting that out of infinite gravitational force)<HR></BLOCKQUOTE>

I consider "inside" to be inside the event horizon, and didn't realize you meant "inside" the singularity.

That happens to be a volume of size zero, so thats why I don't see it as defining "inside"

Re: Theoretical Physics [OT thread]
 

Exactly. Inside a black hole is generally considered to be inside the event horizon.

Another thing: Although none has ever been found, it is possible to have a black hole with an event horizon on the scale of meters, centimeters, millimeters, or smaller.

None of these, nor regular sized black holes, have an infinite gravitational force anywhere, except on the surface of the singularity, which, as someone pointed out, is 'not very big' http://www.shrapnelgames.com/ubb/images/icons/icon7.gif


Derek

Re: Theoretical Physics [OT thread]
 

Well, my understanding is that once inside the event horizon, the object can't escape, and it gravitates towards the singularity, and then becomes part of the singularity. Everything that 'falls' in becomes part of the singularity, and pushes the event horizon outward. As far as I know, there is no way something can stay within the event horizon, but not become part of the singularity.

Re: Theoretical Physics [OT thread]
 

That is true, but there is a finite time before the object actually gets to the center.

Is an object halfway between singularity and event horizon inside or not?

A) It dosen't really matter, but its fun to argue the point, right?


-------------------------

Ah, just thought of why.

You were talking about escaping from a black hole. Escaping is just as "impossible" from 1m inside the horizon, as right in the singularity. The only difference is, if the hole is big enough, your ship can be intact 1m from the event horizon, but will be torn apart (due to gravitational shear) near the singularity and then crushed.

So, it would only be worth trying to escape if your ship wasn't crushed or smeared, but still inside the hole.
Therefore, inside the hole should be inside the horizon.


Note: by gravitational shear, consider the force on your feet vs head as you fall in. 2m from the singularity, the force on your feet is 4x the force at your head, you get smeared alll over.

[This message has been edited by suicide_junkie (edited 01 March 2001).]

Re: Theoretical Physics [OT thread]
 

Yous guys is all stoopid. I happen to know, from watching the Disney movie "The Black Hole," that just inside the event horizon of black holes is a perfect place for evil scientists to have their secret laboratory. Sheesh! Get a ejerkayshun!

Re: Theoretical Physics [OT thread]
 

The speed of light is a constant. The speed of light depends on the media through which the light is travelling... So it's a variable constant?

Magnetising frogs seems a little cruel. How much power would it take to magnetise a human? If you didn't calibrate your field properly and were relying on it to protect against 14g acceleration your spleen could remain weightless as the rest of you was spread over the acceleration couch....

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<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by jimbob55:
The speed of light is a constant. The speed of light depends on the media through which the light is travelling... So it's a variable constant?
<HR></BLOCKQUOTE>

The speed of light (actually any electromagnetic radiation: radio waves, x-rays, gamma rays, etc.) in a vacuum is a constant (roughly 3x10^8 m/s) and that is what the "c" refers to in such equations as E=mc^2.

The speed that light travels is lower than c in various media (e.g. water, atmosphere, glass).

--A Philistine

Re: Theoretical Physics [OT thread]
 

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by a philistine:
The speed of light (actually any electromagnetic radiation: radio waves, x-rays, gamma rays, etc.) in a vacuum is a constant (roughly 3x10^8 m/s) and that is what the "c" refers to in such equations as E=mc^2.

The speed that light travels is lower than c in various media (e.g. water, atmosphere, glass).

--A Philistine<HR></BLOCKQUOTE>


Correct me if I'm wrong but wasn't light made to go faster than c quite recently (quite odd concept, light travelling faster than the speed of light..)

Re: Theoretical Physics [OT thread]
 

You're not wrong. Read the rest of this thread, and the answer you seek, you shall find.


Derek

Re: Theoretical Physics [OT thread]
 

Nobody ever said that the magnet thing would be easy.

But the field would be uniform, and it magnetizes your atoms, not organs, or whatnot. All your atoms would be pulled with the same force, as long as the field is uniform. (otherwise, that frog would have been mush)

[This message has been edited by suicide_junkie (edited 02 March 2001).]