Theoretical Physics [OT thread]

DirectorTsaarx · #1 February 28th, 2001, 04:45 PM

quote:
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.

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"...

Kimball · #2 February 28th, 2001, 05:43 PM

quote:
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.

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.

dmm · #3 February 28th, 2001, 08:08 PM

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).

dmm · #4 February 28th, 2001, 08:20 PM

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.

Kimball · #5 February 28th, 2001, 08:27 PM

dmm

I see. I am engineer, not a physicist. I took just enough physics to be dangerous.

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.

a philistine · #6 February 28th, 2001, 09:45 PM

quote:
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}

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

DirectorTsaarx · #7 February 28th, 2001, 09:51 PM

quote:
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

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...

Dracus · #8 March 1st, 2001, 12:30 AM

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.

capnq · #9 March 1st, 2001, 01:15 AM

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

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

jimbob55 · #10 March 1st, 2001, 01:25 AM

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.