Most people believe that matter can not be accelerated to the speed of light. I say that this is not entirely accurate. Matter can not exist at the speed of light or faster. This may seem contradictary but wait until I am finished. if you were to accelerate , say a marble, to the speed of light, it would be converted to energy. This is the energy needed to push it that last bit bit over the speed of light and into the realm of energy. This explains why light behaves both like a wave(energy) and a particle(matter). Light is the state. between matter and energy.

But it is entirely accurate. Since


Matter can not exist at the speed of light or faster.

then it

can not be accelerated to the speed of light.

I was once told (can't remember by who) that there is a theory out there that matter can't be accelerated to the speed of light but IF it could it would be transformed into something else, say 'anti-matter' (I know anti-matter is NOT this but for the sake of naming things, it is called anti-matter in this case) because I can't remember what they called them, lol. And this 'anti-matter' always travels above the speed of light, and can never decelerate below the speed of light and IF it does, it becomes normal matter.

It is an interesting theory (don't know if it's a theory though, probably not) and it would be nice to think that we could somehow travel faster than the speed of light...but I doubt it. The best way that of travelling great distances in short amounts of time (that is plausible, no matter how implausible) is to bend space.

if you were to accelerate , say a marble, to the speed of light, it would be converted to energy. This is the energy needed to push it that last bit bit over the speed of light and into the realm of energy.

What is the basis for this claim? How does accelerating matter turn it into energy? Many scientists accelerate particles for a living, adding enormous amounts of energy to matter without ever seeing the matter reach the speed of light or become energy.

There is a way to travel great distances in a single lifetime. If you travel at nearly the speed of light, due to relativistic length contraction, objects which were formerly thousands of lightyears away are suddenly much closer and you can easily reach them in a normal amount of time. The problem, of course, is that when you come back to Earth everyone who helped make the ship will be long dead.

How does ^^that^^ work out in relativity? does time dilation have to do with acceleration or with velocity?

other question- if two particles were accelerated to near the speed of light, and passed eachother, what would happen? Would they 'happen' to observe eachother travelling at the speed of light? or would one seem to 'approach' the other at a velocity >c?

@heat, please specify ^^that^^

other question- if two particles were accelerated to near the speed of light, and passed eachother, what would happen? Would they 'happen' to observe eachother travelling at the speed of light? or would one seem to 'approach' the other at a velocity >c?

Well, they could be observed (from our frame of reference) as approaching each other at >c, as well as passing each other at >c, but from their frames of reference, well, here's Einstein's equation for their measured velocities of each other: V=(v1+v2)/(1+(v1)(v2)/(c^2))

BTW, I hear lots of people talking about being converted into energy at c. What is that supposed to mean? That at some point, after many years of gunning your spaceship's engines, your entire ship just goes *poof* and now you are dead and all that remains of you is a flash of light?

Well, at some point I remember coming across (I'll post it when I find it) an quantum version of an old Newtonian equation, and it showed that the energy required to accelerate something to c was not a very high number, but was, in fact, infinity.

Your mass increases with your speed. You cannot accelerate to c as you mass tends to infinity as your speed approaches c meaning you would need an infinite amount of energy to get there.

"Your mass increases with your speed. "
So, you are saying that when you go faster, you contain more matter. That would also mean that either your density or your volume also increase. This doesn't seem right to me...

"Your mass increases with your speed. "
So, you are saying that when you go faster, you contain more matter. That would also mean that either your density or your volume also increase. This doesn't seem right to me...

as your speed increases, so does your energy (kinetic/potential). E=mc^2 (well... let's just simplify things and use this). So yes... in effect, since mass is proportional to energy, as your speed increases, so does your mass

and when I said "^^that^^" I was referring to the twin paradox... time dilation.

HeaT - you have it right in that time dilation explains the one-way trip. When someone approaches a distant object - let's say 250 light years - at .99c, an observer on Earth would see the trip taking about 252.5 years. However, the Earth observer would also notice that time in the reference frame of the spaceship would be ticking slower by about 1/7th (that is, every 7 seconds on Earth would be one second for the traveler). However, in the reference frame of the traveler, time is ticking normally (in fact, Earth's time is slower), but the distance between Earth and the object has contracted by a factor of 7 (the object is about 35 light years away). In both reference frames the traveler as aged about 35-36 years in the journey.

The difficulty in the twin paradox arises if the traveler turns around and returns to Earth (acceleration). During the turn-around, in the traveler's frame, Earth's clock jumps WAY ahead, and even though it will still tick slower in the traveler's frame, Earth's total elapsed time will be much greater than the traveler in all frames. Google "relativistic rocket" for good explanations of acceleration in relativity.

To clear things up a bit for bobfish - when mass is described as being increased by speed, what is being referred to is not mass as we think of it (quantity of matter), but "relativistic mass," which acts as mass in force/momentum equations and is inversely proportional to acceleration. It's equal to m/sqrt(1-(v/c)^2) where m is the "invariant mass" we all know and love (notice how it increases as v increases). Thus the real equation for total energy (kinetic plus rest) is E = mc^2/sqrt(1-(v/c)^2). When there's no velocity, E = mc^2; as velocity approaches c, E approaches infinity.

One more thing I'd just like to add. All these relativistic effects (mass gain, length contraction, time dilation, etc.) are just that. Relative. If you were in a spaceship with no windows , you'd have no way to tell whether you were traveling .0000000001c or .9999999999c (relative to destination). Without any way to see the universe, you'd have no way of knowing which. Until, of course, you slammed into something and created a blast roughly equivalent to the big bang.

Dont you need infinite energy to accelerate something to the speed of light or more? Not sure where i heard it, but it was a while ago. But it would basically mean for anything to go faster then the speed of light, it would have to destroy the universe.

E=mc^2

where:
E = energy
m = mass
c = speed of light

Correct?

edit: nm read the rest of the thread, but im leaving this here :)

One more thing I'd just like to add. All these relativistic effects (mass gain, length contraction, time dilation, etc.) are just that. Relative. If you were in a spaceship with no windows , you'd have no way to tell whether you were traveling .0000000001c or .9999999999c (relative to destination). Without any way to see the universe, you'd have no way of knowing which. Until, of course, you slammed into something and created a blast roughly equivalent to the big bang.

Even if the craft had windows, it would be perfectly valid to surmise that all outside is moving with uniform velocity and that you remain at rest.

@wolfy E=mc^2, doesn't refer to what you want it to. It refers to potential energy of on object capable of being turned into energy via exothermic reaction. It doesn't take much matter to make alot of energy, however it takes alot of energy to make matter.

@wolfy E=mc^2, doesn't refer to what you want it to. It refers to potential energy of on object capable of being turned into energy via exothermic reaction. It doesn't take much matter to make alot of energy, however it takes alot of energy to make matter.

That would depend upon context. But it is strictly not potential energy in the sense physicists use it, because in special relativity all motion is inertial and thus the potential energy of bodies is zero, because there are no external forces.

The E can be the energy required to create a particle of mass m, say in a one loop diagram, where a mater-antimatter pair is created, but is more often used to refer to the rest energy of a body of rest mass m or kinetic energy of a body of relativistic mass m.

Your mass increases with your speed. You cannot accelerate to c as you mass tends to infinity as your speed approaches c meaning you would need an infinite amount of energy to get there.

would 'your inertial mass' perhaps be a better way of saying it?

Would you have a higher gravitational pull, or would it just be more difficult to change directions?

I imagine with time dilation, as you pass by a planet, since to you it would seem you are going through the field of gravity for a relatively short time (compared to what the planet sees), that would mean you would experience a disproportionately low deflection due to it, which is consistent with the idea of inertia, but not mass, increasing.

This could all be bullshit, I'm pulling it out my ass every step of the way.

would 'your inertial mass' perhaps be a better way of saying it?

Would you have a higher gravitational pull, or would it just be more difficult to change directions?

I imagine with time dilation, as you pass by a planet, since to you it would seem you are going through the field of gravity for a relatively short time (compared to what the planet sees), that would mean you would experience a disproportionately low deflection due to it, which is consistent with the idea of inertia, but not mass, increasing.

This could all be bullshit, I'm pulling it out my ass every step of the way.

Yes, inertial or relativistic mass (as distinct from rest mass) is clearer and more accurate.

In a way it does increase gravitational "pull", as the body would have a greater kinetic energy.

A particle with mass would have to become massless to achieve c. It's that simple.

We just went over this in class today. Let's start with Newton's 2nd law, F=ma. This can also be written as F=m (dp/dt), which means a force is equal to a rate of change in momentum. To clarify, momentum is mass times velocity, and since a change in velocity is an acceleration, and an acceleration is defined as a rate of change in velocity, so this all makes sense. Now, this equation is not quite correct due to Newton not knowing anything about relativistic effects. In reality force is equal to your rate of change in relativistic momentum. (Note also that when I say "time" or am talking about "rates" I mean from an observer's inertial reference frame, which means that he is not accelerating. The time according to the thing moving really fast is different). But what is your relativistic momentum? It is mass times velocity times the Lorentz factor, γ (gamma), which is (1-(v^2/c^2)^-1/2, where c is the speed of light = 3e8m/s. It can be written simply as Prel= γmv. So we can think of a force as the rate of change of relativistic momentum, or F=d(γmv)/dt. This can also be written F=(γm) dv/dt, or F=γma. This means that your mass is actually γm, which in expanded form is m/(1-(v^2/c^2)^1/2. What happens when you increase v? The quantity (v^2/c^2) approaches 1, so the quantity in the denominator approaches zero, which makes the mass approach infinity as v approaches c. Also, since m increases, the force needed to accelerate it towards c increases until an infinite force is required to get it to c. This also means that an infinite amount of energy is required to move it any sort of distance. (W=Fd).

However, if your mass is zero then you can go the speed of light, which is exactly how light does it. In fact, you'll always be moving at c.

So we can think of a force as the rate of change of relativistic momentum, or F=d(γmv)/dt. This can also be written F=(γm) dv/dt, or F=γma. This means that your mass is actually γm, which in expanded form is m/(1-(v^2/c^2)^1/2.

you have to remember to keep the gamma inside of the derivative since it is time dependent. then m*d(v/(1-(v/c)^2)^1/2)/dt = γ^3ma