Thread: speed of light

uh, why cant we go at the speed of light again?

As speed increases mass also increases, so that more energy is required to accelerate the increased mass to higher speeds. It would take infinite energy to achieve light speed.

Photons do it instantaneously because they have no rest mass.

Why is this? It's just the way things are.

As John said, attempting to go to the speed of light results in ever larger mass and consequently ever larger amounts of energy. At the speed of lighjt, mass is infinite. Consequently, the energy becomes infinite, so no hope of ever going as fast.

No, please do not say that the mass increases. This is physically wrong.

http://en.wikipedia.org/wiki/Mass_in...c_mass_concept

You can mathematically express the increase of energy needed to attain higher velocities as an increase of the mass, but it is in fact not true. The real reason is that the total relativistic energy does not increase linearly like the classical kinetic energy, but is modified with the gamma factor.



If you say that the mass increases, you immediately suggest that the gravitational force increases as well. But this is not true either. So, either you clearly specify, what you mean with an increase of mass, or you explain it in a different way.

Inertia increases? Would that be accurate enough? I.e. attempts to affect the velocity of the particle parallel to its motion in either direction would require more and more energy, the nearer the velocity comes to C, to gain the same acceleration.

Originally Posted by KALSTER

Inertia increases? Would that be accurate enough? I.e. attempts to affect the velocity of the particle parallel to its motion in either direction would require more and more energy, the nearer the velocity comes to C, to gain the same acceleration.

Yes, inertia. That would be accurate.

If you say that the mass increases, you immediately suggest that the gravitational force increases as well. But this is not true either

Wouldn't the principle of equivalence require that? SDaty an observer moves close to the speed of light, constantly accelerating. Now, the principle of equivalence states that he will not be able to differentiate between a stronger gravitational field and his own acceleration . i. e no way to state what exactly is happening. If, we assume, he was completely alone, then obviously he would have to measure either acceleration or a stronger graviational field, the source of which can only be himself. A stronger gravitational field implies greater mass.

Wouldn't you say then, that, logically speaking, the principle of equivalence demands an increase in mass? After all, initial mass is equivalent to gravitational mass. If one increases, then naturally so does the other.

That would be true for the obeserver in the accelerated reference frame, but not for someone outside that frame. An external observer would not experience an increase of the gravitational force of the accelerated particles.

correct me if im wrong, but isnt there also something about how time slows the faster you travel, and somehow time distorts in such a way that you can never reach the speed of light? im not sure about the details, but is there such a thing?

Originally Posted by Liongold

If you say that the mass increases, you immediately suggest that the gravitational force increases as well. But this is not true either

Wouldn't the principle of equivalence require that? SDaty an observer moves close to the speed of light, constantly accelerating. Now, the principle of equivalence states that he will not be able to differentiate between a stronger gravitational field and his own acceleration . i. e no way to state what exactly is happening. If, we assume, he was completely alone, then obviously he would have to measure either acceleration or a stronger graviational field, the source of which can only be himself. A stronger gravitational field implies greater mass.

Wouldn't you say then, that, logically speaking, the principle of equivalence demands an increase in mass? After all, initial mass is equivalent to gravitational mass. If one increases, then naturally so does the other.

There are a couple of things wrong with this.

If a observer accelerates at a fixed acceleration, he wouldn't be able to tell his acceleration from a gravitational field of a fixed strength. For example if he accelerates at 9.8m/s^2, it is the same as standing still in a 1g gravity field. As he maintains this acceleration and he nears the speed of light, he will not feel any increase in gravity.

Secondly, the equivalent gravity field would have to originate from outside the observer. For example, if traveling in a spaceship, it would have an apparent origin underneath the floor he is standing on. This not what the observer would experience from an increase in his own gravitational mass.

So the guy in the spaceship would experience 1 G indefinitely, no matter how close he comes to C? This would make sense from an increase in inertia perspective I think. How could the spaceship determine how fast it is going from inside the spaceship (when limiting accuracy of his instruments means he cannot do it by direct observation of the observer), or is it impossible?

The speed of light on earth is slower than the speed of light in a vacuum right? So is there a limit to how slow light can go? Can we stop light in its tracks?

The speed of a photon is the same on Earth as anywhere else. The overall average speed of a large group of photons is reduces by passing through material.

And yes, photons can be trapped. I don't know the details of how this works, just that it can be done.

If you're asking how large (right word?) of an index of refraction a material can have, that I don't know, but it'd be cool to see a material you could walk around and see your own image. Of course, a high index of refraction does more than just slow down the light. It also bends it more, so such a material may not be particularly transparent anyway.

Here is an interesting link for FTL.

http://math.ucr.edu/home/baez/physic...Light/FTL.html

Apparently there are many ways to go faster than light.

The two options that people seem to be talking about that could apply to a space ship are worm holes and warp bubbles.

Someone at work thought that there was a third theory, but I cannot recall what that one was about.

Don't warp bubbles suggest changing the laws of physics (or the speed of light)? Not sure but that's the impression I got. As for wormholes you are not travelling past the speed of light, you are just travelling a smaller distance (like drilling your way to China, ya I know that wouldn't work).

The two options that people seem to be talking about that could apply to a space ship are worm holes and warp bubbles

Firstly, while wormholes are theoretically possible, they do not entail going faster than light, simply hopping from one point to another using a 'shortcut'.

What, by the way, is a warp bubble?

Secondly, the equivalent gravity field would have to originate from outside the observer. For example, if traveling in a spaceship, it would have an apparent origin underneath the floor he is standing on. This not what the observer would experience from an increase in his own gravitational mass.

Thank you, Janus.

I'm pretty sure that warp bubble is referring to an Alcubierre drive, which creates a bubble of warped space to move the object without having it exceed the speed of light locally. It's a cool idea, but not without problems.

Originally Posted by Golkarian

Don't warp bubbles suggest changing the laws of physics (or the speed of light)? Not sure but that's the impression I got. As for wormholes you are not travelling past the speed of light, you are just travelling a smaller distance (like drilling your way to China, ya I know that wouldn't work).

I don't think warp bubbles require changing the laws of physics. However, there is debate about whether it would work.

I think the analogy of "drilling to China" is closer to the worm hole concept.

Liongold:

Magimaster gives a link to the Alcubierre drive on Wikipedia that has the relevant references in the bibliography. I think Alcubierre gets the credit for starting the "warp bubble" idea w/ a letter to the editor he wrote in 1994. My understanding is that a wave of expanding space-time could propel a space ship contained in a warp bubble.

The bubble moves faster than light. The space ship does not move in the bubble.
The concept requires enormous energy.

Originally Posted by Liongold

The two options that people seem to be talking about that could apply to a space ship are worm holes and warp bubbles

Firstly, while wormholes are theoretically possible, they do not entail going faster than light, simply hopping from one point to another using a 'shortcut'.

What, by the way, is a warp bubble?

Secondly, the equivalent gravity field would have to originate from outside the observer. For example, if traveling in a spaceship, it would have an apparent origin underneath the floor he is standing on. This not what the observer would experience from an increase in his own gravitational mass.

Thank you, Janus.

Wormholes, if they were to permit one to travel through them would in fact be a means of getting from point A to point B faster than a photon, by taking a different route. However, the available theory indicates that womholes, if they exist at all, cannot be held open without the existence of a HUGE amount of "negative energy" and hence would not provide a viable route for the travel of either matter or information.

Moderator note:

Certain posts in this thread have been split off to a thread in pseudoscience.