[Tony Speer]

Tony Speer  asked the Naked Scientists:

Dear Chris,

If speed is relative then why is it you can't go past the speed of light? For example if you had a space ship that had a infinite amount of energy and there was nothing else in the universe and you tried to go fast as you could then why can't you go past the speed of light? How would you even know your moving at all?

Tony Speer from Caldwell, Idaho in the US

What do you think?

[lightarrow]

Tony Speer  asked the Naked Scientists:

Dear Chris,

If speed is relative then why is it you can't go past the speed of light? For example if you had a space ship that had a infinite amount of energy and there was nothing else in the universe and you tried to go fast as you could then why can't you go past the speed of light? How would you even know your moving at all?

Tony Speer from Caldwell, Idaho in the US

What do you think?

If there is nothing else in the universe then you can't measure the ship's speed, so you can't even say that you can go faster than light's speed...

[DoctorBeaver]

Plus infinite energy is a nonsense; it cannot be acheived.

[DarthTutor]

Velocity is relative for sure, however the constant of nature "c" we usually call "the speed of light in vacuum" is not relative. The main reason for this is that the origin of this constant is rather unrelated to light but embedded in the geometry of "Spacetime". The fact that space and time together form a single entity calls for the existence of a fundamental constant that allows the conversion of length-units into time-units. This constant typically takes the unit meters-per-second (or seconds-per-meter if you please). That constant better be "asolute" for all observers in order for the idea of spacetime to make any fundamental sense.
With this as a starting point it is fairly straightforward to show that clocks in relative motion suffer a relative time-dilation that increases with increasing relative speed. This time-dilation effectively becomes infinitely large when the relative speed approaches the value of c. As a result any acceleration driving you to higher velocities gets bogged down by ever increasing time-dilation in a struggle to reach "c" that it cannot win. Saying that it requires infinite energy or infinite momentum to attain the speed "c" is effectively the same thing.

[DoctorBeaver]

DarthTutor - nicely put.

[LeeE]

To accelerate you need to use energy.  At low speeds the amount of energy you have to use to go faster seems to follow a linear relationship - put in a bit more energy and you'll go proportionally faster - but once you start approaching the speed of light the relationship between how much energy you use and how much faster you go trails off and instead your mass increases, your rate of time decreases and your length, in the direction you're traveling in, also decreases.

Although this seems weird, it might help if you separate out the different factors of the situation.  These are mass (from the matter comprising the object being accelerated) and distance and time (from velocity), and all of these are actually affected when you apply energy to something to make it move.  As I said earlier, at low speeds, nearly all of the energy goes into moving the mass over the distance in the period of time, but as you get faster and faster the energy you put in begins to have more of an effect on the other factors instead i.e. mass, distance and time.

Now as to why there should be an upper speed limit is still one of the unsolved mysteries of the universe but it's been proved satisfactorily enough that as the velocity of something approaches the speed of light we do actually start to see the effects upon mass, distance and time.  This has been demonstrated in lots of experiments, from comparing pairs of clocks at different altitudes, where the slight difference in gravitational strength simulates acceleration, to comparing clocks where one is moving and one is stationary.  Perhaps the best demonstration though, is in particle accelerators such as the LHC (cough), where unstable particles start living much longer than they would normally do and where more energy is needed to keep them on course than would be the case if their mass didn't increase.

The relationship between an object's velocity and the relativistic effects such as time dilation, foreshortening and mass increase is actually quite simple and follows a circular sin law.  It's perhaps easiest to show if we normalise the speed of light to '1' and use Pythagorus, where the hypotenuse represents the speed of light - 1, to get a factor we can multiply the normal rates of time and length by to get the relativistic values.

For example, if our velocity (v) is zero then the factor for our rate of time will be:
  SQRT(c^2 - v^2)
= SQRT(1^2 - 0^2)
= SQRT(1)
= 1

So multiplying the normal rate of time by 1 gives us time passing at 100% of it's normal rate.  However, if we've got up to half the speed of light, so v = 0.5, we get:
  SQRT(1^2 - 0.5^2)
= SQRT(1 - 0.25)
= SQRT(0.75)
= 0.866025404

And now time will only be passing at 86.7025404% of it's normal rate i.e. slower.  Relativistic length contraction follows the same rule but for mass increase you need to divide the normal mass by the factor instead of multiplying it, so the mass increase at 0.5 'c' would be 1.154700538 times it's normal mass.

Now if you try to get factors for speeds greater than the speed of light - say 1.5 times 'c' we'd get:
  SQRT(1^2 - 1.5^2)
= SQRT(1 - 2.25)
= SQRT(-1.25)
= ERR   []

[Will]

Why the focus on the infinitely large E? With constant energy, I would suspect that smaller masses would achieve the same effect.
I'm way out of my league here and this is a very simplistic approach. But, if you rearrange the equation, you get c=sqrt(E/m). Given that c is a constant, the ratio of E/m must be constant. Therefore, one must conclude that at infinitely small mass, energy must be equally small (something like zero)? Perhaps in this realm of the unbelievably tiny, energy and mass are so much alike that they are actually entangled. What happens if that entangled state were disrupted? Would E still = mc^2?
Just a random thought......

[lyner]

I think you have ignored the fact that the energy you have put into getting the object to go 'very fast' has, effectively, increased its mass (a relativistic increase in mass - sorry lightarrow but it seems the easiest way to put it). So it requires even more energy to get it to go 'a bit faster'.

[lightarrow]

Why the focus on the infinitely large E? With constant energy, I would suspect that smaller masses would achieve the same effect.
I'm way out of my league here and this is a very simplistic approach. But, if you rearrange the equation, you get c=sqrt(E/m). Given that c is a constant, the ratio of E/m must be constant. Therefore, one must conclude that at infinitely small mass, energy must be equally small (something like zero)? Perhaps in this realm of the unbelievably tiny, energy and mass are so much alike that they are actually entangled. What happens if that entangled state were disrupted? Would E still = mc^2?
Just a random thought......

Just some threads after this one, there is the thread:
"Do photons have energy equivalent mass at light speed?":

that equation is valid ONLY at zero velocity.
You have to use this one E² = (cp)² + (mc²)².
if m = 0 (e.g., photons) then E = cp; photons do have momentum (even classical light) so they have energy.

[edgeArchitect]

Why the focus on the infinitely large E? With constant energy, I would suspect that smaller masses would achieve the same effect.
I'm way out of my league here and this is a very simplistic approach. But, if you rearrange the equation, you get c=sqrt(E/m). Given that c is a constant, the ratio of E/m must be constant. Therefore, one must conclude that at infinitely small mass, energy must be equally small (something like zero)? Perhaps in this realm of the unbelievably tiny, energy and mass are so much alike that they are actually entangled. What happens if that entangled state were disrupted? Would E still = mc^2?
Just a random thought......

My apologies for raising the old thread.

I was trying to address the same issue, on a completely unrelated forum, and I, too, came up to this formula your mentioning and google it.

c=sqrt(E/m)

This is also quite a bit out of my league,

In layman terms if this is true, then is it possible that c is not only the speed of light in a valuum, but also a density of space in which a mass of a photon equals to 0 ( <1×10−18 eV actually ( newbielink:http://en.wikipedia.org/wiki/Photon [nonactive]))

And, if everything is relative, then would it be false to assume that a mass of a photon is actually the energy/ratio of itself comparing to the new 0 mass:

a Energy of a yet undiscovered density ( which is most likely outside of our observable spectrum or  further than 13 billion - 1.3x10^-10 eV ) = ~1×10^−18 eV / (3x10^8)^2


Not sure if the numbers (i dunt know how to convert these into something solvable) are correct, but hopefully you see the logic.



ruslan

[Bill S]

"infinitely small mass"

.

Will, how do you distinguish between "an infinitely small mass" and "nothing"?

[lightarrow]

I was trying to address the same issue, on a completely unrelated forum, and I, too, came up to this formula your mentioning and google it.
c=sqrt(E/m)

To what you want to apply that formula?

[Vereava]

So basically, in order to go the speed of light, you would need an infinite amount of mass to create an infinite amount of energy which you would be burning off for an infinite amount of time?

[lightarrow]

So basically, in order to go the speed of light, you would need an infinite amount of mass to create an infinite amount of energy which you would be burning off for an infinite amount of time?

But the more mass you start with, the more energy you need to accelerate it...

[Farsight]

If speed is relative then why is it you can't go past the speed of light? For example if you had a spaceship that had a infinite amount of energy and there was nothing else in the universe and you tried to go fast as you could then why can't you go past the speed of light?

You can't go faster than light because you are, in essence, made of it.

That might sound unfamiliar, but look to the hard scientific evidence, and it's simple. You know you're made of protons and electrons, and neutrons too. But a free neutron decays into a proton an electron and an antineutrino, so forget about neutrons. Forget about neutrinos too because they muddy the waters. That leaves the electrons and protons, and they have spin angular momentum. We can make them out of light in pair production, and we can destroy then in annihilation. What we then get is light:



In the electron and the proton, the light it isn't moving linearly at c. Instead it's going round and round, spinning. You are made of this light, and you cannot go faster than the light from which you're made. 

[Vereava]

So basically, in order to go the speed of light, you would need an infinite amount of mass to create an infinite amount of energy which you would be burning off for an infinite amount of time?

But the more mass you start with, the more energy you need to accelerate it...

Well, if you have an infinite amount of both, then that's not an issue... I understand what you're saying, I was just trying to reach a logical possibility based off of the information you provided.

[lightarrow]

You can't go faster than light because you are, in essence, made of it.
...
In the electron and the proton, the light it isn't moving linearly at c. Instead it's going round and round, spinning. You are made of this light, and you cannot go faster than the light from which you're made. 

You should have told him that this is just your theory and nothing more.

[Farsight]

Pair production, annihilation, electron spin, the Einstein de-Haas effect, and electron diffraction and refraction aren't my theory, lightarrow. What they tell you is that we can create an electron out of light, then within that electron something is going round and round, that the electron behaves like light in certain respects, and its annihilation releases light. So what's the electron made out of? Cheese?

[Bill S]

Whatever kind of cheese electrons might be made of []; we have another problem which could be even more serious.  We talk glibly about infinite quantities, but do we really think about the implications of this?  Cantor may have tamed mathematical infinities, but physical infinity is a very different thing.  It is easy to confuse "infinite" with "boundless", but they are not the same.

[lightarrow]

Pair production, annihilation, electron spin, the Einstein de-Haas effect, and electron diffraction and refraction aren't my theory, lightarrow.

The fact an electron is "made of light" *is* your theory and you know very well I was referring to that.