Can the speed of light be considered infinite?

[Hanpan]

Actually certain particles called tachions sp? are theorecticized to excist. These are particles that allways travel faster than the speed of light and can never be slowed down below it.

 

[techweenie]

Like someone posted, light travels at different speed through different mediums. Why don't they look more into bending space, so that 2 points are right next to each other? It worked in the movies!

 

[hammer01]

Actually the speed of gravity is considered to be considerably greater than the speed of light, but because it is a force and has no mass is generally not considered because we can in no way (as of this time) use that speed to any effect. Here is a link to one article and here is another.

 

[Tomek]

A tachyon is a theoretical particle that is supposed to travel faster than the speed of light. They are also supposed to generate Cerenkov radiation. But seeing how nobody has been able to detect Cerenkov radiation in vacuum the existence of tachyons is highly debatable. And if they do exist they would cause quite a bunch of faster than light paradoxes. So there seem to be three possibilities:
1) tachyons do not exist,
2) tachyons exist but can't be used to send faster than light signals
3) tachyons exist and can be used to send faster than light signals, but some special provision will keep anyone from using them since that would cause an unsolvable paradox

 

[Tomek]

A gravitational field is basically a curvature of spacetime; it has no mass so I don't think it should even be considered. Besides what you're suggesting is instantaneous action at a distance, something that violates relativistic causality. Nice try though

 

[Elledan]

<< A tachyon is a theoretical particle that is supposed to travel faster than the speed of light. They are also supposed to generate Cerenkov radiation. But seeing how nobody has been able to detect Cerenkov radiation in vacuum the existence of tachyons is highly debatable. And if they do exist they would cause quite a bunch of faster than light paradoxes. So there seem to be three possibilities:
1) tachyons do not exist,
2) tachyons exist but can't be used to send faster than light signals
3) tachyons exist and can be used to send faster than light signals, but some special provision will keep anyone from using them since that would cause an unsolvable paradox >>


You know, there's a reason why string theory didn't make it and was replaced by super string theory, which does not require these mysterious tachyon particles

 

[Elledan]

<< Like someone posted, light travels at different speed through different mediums. Why don't they look more into bending space, so that 2 points are right next to each other? It worked in the movies! >>


What you describe is commonly known as a 'warp-drive', and is possible in theory, yet faces quite some challenges before we can use it for space-ships.

 

[Tomek]

ahh, but what I want to see is how ToE (Theory of Everything) will solve the paradoxes between QM and GTR... I'm particularly interested in the problem of Cosmic Censorship and naked singularities, thought by many to be the most important question in GTR

 

[Tomek]

bending spacetime would require creating a wormhole, unfortunately our feeble technology does not allow that...

 

[Milkman95]

Everyone does realize that is posible that we don't even really know what we are arguing about because our understanding of "physics" is not nearly developed as much as some would like to think. Most of the "Law's of Physics" don't fully explain this stuff(i don't think), and the "theory of relativity" (among other theorys) is just that.. a theory. It might be a very good one, but its a theory none the less.

Again a post by me with nothing to back up anything i say!

 

[Elledan]

<< bending spacetime would require creating a wormhole, unfortunately our feeble technology does not allow that... >>




<< A theory about "warp drive": Using the formalism of general relativity, it has been shown that faster than light travel may be possible (ref 7). All you need to do is contract spacetime in front of your ship and expand spacetime behind your ship. This "warped" space and the region within it would propel itself "with an arbitrarily large speed" (ref 7). Observers outside this "warp" would see it move faster than the speed of light. Observers inside this "warp" would feel no acceleration as they zip along at warp speed.

So what's the catch? First, to expand spacetime behind the ship you'll need matter having a negative energy density like negative mass, and lots of it too. It is unknown in physics whether negative mass or negative energy densities can exist. Classical physics tends toward a "no," while quantum physics leans to a "maybe, yes." Second, you'll need equal amounts of positive energy density matter, positive mass, to contract spacetime in front of the ship. Third, you'll need a way to control this effect to turn it on and off at will. And lastly, there is the debate about whether this whole "warp" would indeed move faster than the speed of light. To address this speeding issue, the theory draws on the "inflationary universe" perspective. The idea goes something like this: Even though light-speed is a limit within spacetime, the rate at which spacetime itself can expand or contract is an open issue. Back during the early moments of the Big Bang, spacetime expands faster than the speed of light. So if spacetime can expand faster than the speed of light during the Big Bang, why not for our warp drive?

Just prior to the publication of the above theory, there was a workshop held at JPL to examine the possibilities for faster-than-light travel (ref 8). Wormholes, tachyons, and alternate dimensions were just some of the topics examined. The conclusions from this informal two-day workshop are as follows:

(1) Faster-than-light travel is beyond our current horizons. Not only is the physics inadequately developed, but this physics is not oriented toward space propulsion or toward laboratory scale experiments.

(2) Causality violations (where effect precedes cause) are unavoidable if faster-than-light travel is possible, but it is uncertain whether causality violations are themselves physically prohibited.

(3) A few experimental approaches are feasible to address the science associated with faster- than-light travel, including:

(a) Search for evidence of wormholes using astronomical observations: look for a group of co-moving stars or for the visual distortions indicative of a negative mass hole entrance.

(b) Measure the velocity of light inside a Casimir cavity (between closely spaced conductive plates) to search for evidence of negative space energy. This pertains to wormholes, tachyons, and the negative energy density issue.

(c) Resolve the rest mass issue of the Neutrino, determining whether the unconfirmed experimental evidence of imaginary mass is genuine.

(d) Study cosmic rays above the atmosphere, using scattering targets of know composition to look for characteristic evidence of tachyons and more general particle physics events.

>>



http://www.lerc.nasa.gov/WWW/PAO/html/warp/ipspaper.htm

 

[Elledan]

<< ahh, but what I want to see is how ToE (Theory of Everything) will solve the paradoxes between QM and GTR... I'm particularly interested in the problem of Cosmic Censorship and naked singularities, thought by many to be the most important question in GTR >>


Cosmic Censorship?

 

[PaNsyBoy8]

About light and slowing it down, scientist have found a way to stop light completely. My old physics professor was into light for his research and he was telling us about it.

and no answer the question, no light isn't infinite, you can't travel the speed of light but you can travel faster.

 

[IndyJaws]

<< bending spacetime would require creating a wormhole, unfortunately our feeble technology does not allow that... >>



Yeah? Well wait until the Athlon XP 2000+ comes out and then we'll see

Actually, Tomek, I appreciate all your contributions to this discussion. I've learned quite a bit

 

[Milkman95]

<< A theory about "warp drive": .....

.....Just prior to the publication of the above theory, there was a workshop held at JPL to examine the possibilities for faster-than-light travel (ref 8). Wormholes, tachyons, and alternate dimensions were just some of the topics examined. The conclusions from this informal two-day workshop are as follows:

1) Faster-than-light travel is beyond our current horizons. Not only is the physics inadequately developed, but this physics is not oriented toward space propulsion or toward laboratory scale experiments.

(2) Causality violations (where effect precedes cause) are unavoidable if faster-than-light travel is possible, but it is uncertain whether causality violations are themselves physically prohibited.


>>



THis started off good.. and i was totally understanding it.. then... BOOM.. i think my head just exploded! Thanks for the info.. someday i will try to figure this out.

 

[rgwalt]

<< A gravitational field is basically a curvature of spacetime; it has no mass so I don't think it should even be considered. Besides what you're suggesting is instantaneous action at a distance, something that violates relativistic causality. Nice try though >>



Nice try for you too... Gravity is an instaneous effect. "Action at a distance" applies here. The reason is that a mass curves space time around it in such a way that it creates a gravitational field. If one were to instantly remove the sun from the center of our solar system, we would instantly be able to detect the effects on earth even though the suns rays would still be beating down on us for 8 more minutes.

Ryan

 

[conjur]

"ticking away...the moments that make up a dull day."

 

[Tomek]

http://ahobon.reduaz.mx/~valeri/ch-prop.txt

Newton was the one that advocated action at a distance, however the effect is inadmissible in GTR! Newton's laws are, after all, just an approximation of what really happens.

 

[Tomek]

<< Cosmic Censorship? >>



I'm assuming that you know what a singularity is... a naked singularity is basically a singularity that exists outside of a black hole, a singularity without an event horizon. Naked singularities can lead to a breakdown of predictability and determinism, among many other things. The cosmic censorship hypothesis basically forbids the existence of naked singularities (it comes in two tastes though: weak and strong).

Here's the term paper I wrote (rough draft) regarding the topic, it's not exactly complete yet so be warned...
http://www.students.uiuc.edu/~sarotara/Singularities.doc

 

[Tomek]

<< Gravity is an instaneous effect. "Action at a distance" applies here. The reason is that a mass curves space time around it in such a way that it creates a gravitational field >>




rgwalt, the curvature of spacetime does not create a gravitational field; a curvature of spacetime is the gravitational field... and this would imply that the curvature propagates through spacetime faster than light, something that GTR forbids

 

[Harvey]

<< The speed of light is about 3x10^8 m/s. No more, no less. Ever. >>

I'm just speculating, but the fact that a prism bends light at a different rate across the specrum suggests that the speed of light at different frequencies does vary through different materials.

 

[hammer01]

Harvey yes light does travel at different speeds through different substances, the commonly accepted speed of light is for light traveling in a space vacuum. Tomek, actually if gravity does have a speed that is possible to measure then by definition it would not be instantaneous action. There are folks that also believ that the speed of light (and of gravity) is actually slowing with the expasion of the universe (theory now and fanciful at that but possible) and that at one time light actually traveled much faster than it does today (say a few seconds after the big bang).

 

[BD2003]

Heh, leave it up to ATOT to go off on a tangent almost totally unrelated to the original topic...

Anyways, I'm trying to settle an argument between some friends of mine here, so a simple yes or no would suffice. It requires a bit of imagination.

Speaking STRICTLY of the person traveling at light speed (no warping) in their little spaceship...

Someone is approaching c as close as possible as c can be approached without being infinitely massive. How and where the energy to do this came from is not the issue. To that person, due to time dilation effects, couldnt they theoretically reach anywhere in the universe in an instant? And therefore to that one person in their little ship, couldnt it be argued that they are going infinitely fast, regardless of how many zillions of years have passed in the normal everyday universe?

 

[Milkman95]

No.

 

[khtm]

I was too lazy to read the entire thread, but the light speed barrier HAS been broken. This happened in July of last year.

linky

Taught in physics classes the world over, Albert Einstein?s theory of special relativity holds that no object or information can move faster than the speed of light in a vacuum, or 186,000 miles (300,000 kilometers) per second. But NEC?s Lijun Wang says he created an experiment in which a light beam raced through a gas-filled chamber so quickly, it exceeded the speed of light by a factor of 300. What?s more, the light pulse appears to have left the confines of the chamber before it even entered ? a seemingly impossible occurrence according to theories of causality, which predict that causes must always precede their effects.