# Faster than Light

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Why can't we *or something we create* go faster than the speed of light? What limits us? Is it an actual physical reason or just a theoretical reasoning based on some really advanced math and physics?

somebody described it to me once as saying that the funtion 1/x will never reach zero. As x goes to infinity, the limit will be zero, which i think means it will get infinetesimally close to zero, yet never reach it. They said to think of light speed in this way.

Well, if they are right, I understand it, but what disallows us from going 3.09x10^8 meters pers second?

Whats holding us back?

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we'd need infinite energy to accelerate to the speed of light. the energy in the universe is finite. therefore, speed of light cannot be reached.

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You may be wondering why it would take an infinite amount of energy.

The reason is that as particles, that have mass to begin with, accelerate to near the speed of light, their mass becomes infinitely heavy, which in turn creates the need for the infinite energy to move the aforementioned mass.

That's why photons can go the speed of...light. They are massless.

Hope this helps

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http://www.technologyreview.com/blog/arxiv/23292/

MIT Technology Review: "FTL travel not possible after all"

http://www.centauri-dreams.org/?p=7101

arcane professional research paper:

http://arxiv.org/abs/0904.0141

The research paper is co-authored by Stefano Liberati (world class guy).

the FTL issue depends somewhat on whether your model is special relativity (vintage 1905 SR) or general relativity (vintage 1915 GR). Both are called "relativity" and both are courtesy Albert Einstein. Both indicate that you can't approach a given destination at a rate that is FTL (greater than or equal to c) but for somewhat different reasons.

SR says that FTL without warp drive doesn't work because vehicle inertia grows without limit as it approaches c.

GR says that FTW with warp drive doesn't work because you would have to deform the geometry of space in a way that would kill anything inside the deformed "bubble" region. Moreover, producing a "bubble" of exotic geometry would require a form of energy so far unknown to physics. And moreover if ever produced, the bubble would self-destruct---it would not be stable. (The discovered instability is what Liberati's paper is about.)

This is all very interesting. But scientific theories are not meant to be believed, rather they are meant to be tested and re-tested and if necessary revised. It is risky to predict the future of research and human knowledge.

Edited by Martin
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It should be noted that all of this is relative to something else. There is no such thing as absolute velocity. It would take infinite energy to accelerate you to C relative to me, and you would have infinite momentum relative to me. You yourself would never get any closer to C in any absolute sense, nor notice any difference in yourself. No matter how long you've been accelerating and how much energy you expend doing so, the light from your headlights and taillights still both move at C away from you. This is true even though from my perspective the light from your headlights might appear to only be moving slightly faster than you (since it is moving at C relative to me, as well, and you are moving at almost C relative to me). This is an important concept in relativity: that light always moves at the same speed relative to everyone, including observers moving relative to one another. If that seems like a paradox, that's normal. The attempt to make sense of that observed and apparently paradoxical fact is what led to special relativity.

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So, even if I was going the speed of light, light would still be going faster than me? because it would be relative to me? Then shouldn't someone on the ground see the light going a speed of 2c ?

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So, even if I was going the speed of light, light would still be going faster than me? because it would be relative to me? Then shouldn't someone on the ground see the light going a speed of 2c ?

You can't go the speed of light. But if you were going at almost the speed of light, say 0.9C relative to the Earth, then yes, it would still be going at fully 1C faster than you. A person on the Earth would not see the light going at 1.9C, though, only 1C. To us it would look like the light was only going 0.1C faster than you. This is possible because velocity, time, and distance are not universally constant things, but depend (among other things) on the velocity of the observer. That's what relativity is all about.

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So, even if I was going the speed of light, light would still be going faster than me? because it would be relative to me? Then shouldn't someone on the ground see the light going a speed of 2c ?

"Someone on the ground" would see your headlight at c and you right behind it at almost c. Because of time dilation, you would see your headlight moving away from you at c. Since your second is very long relative to Earth time, the separation speed that seems slow to Earth is fast to you.

If you could generate 1 G of continuous thrust in a rocket your would never quit accelerating but you would also never reach c. You would however go 100,000 light years in just 12 years on your clock. Over 100,000 years will pass on Earth though.

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Then shouldn't someone on the ground see the light going a speed of 2c ?

In special relativity velocities do not sum in the same way as they do in galilean relativity (which is what we use every day for normal speeds).

Gives a simple over view.

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• 3 weeks later...
Why can't we *or something we create* go faster than the speed of light? What limits us? Is it an actual physical reason or just a theoretical reasoning based on some really advanced math and physics?

somebody described it to me once as saying that the funtion 1/x will never reach zero. As x goes to infinity, the limit will be zero, which i think means it will get infinetesimally close to zero, yet never reach it. They said to think of light speed in this way.

Well, if they are right, I understand it, but what disallows us from going 3.09x10^8 meters pers second?

Whats holding us back?

I hope the prevoius posts have answered your questions. I would like to add that in a dielectric media the light velocity is smaller than c, and there are particles moving in the media with v>c. If such a particle is charged, it emits Cherenkov's radiation (I mean the media+charge both work on radiation). If such a particle is neutral, no radiation is produced. So it can be faster than light. Nothing special.

Bob.

Merged post follows:

Consecutive posts merged

Another trick: Take a rectangle and launch a fast particle from one corner to the closest side (a short-cut), and launch the light along the rectangle diagonal from the same corner at the same time (a long-way). It is well possible that the particle reaches the opposite side before the light.

Bob.

Edited by Bob_for_short
Consecutive posts merged.

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