Home Forum Chat Forum Physics fans and others who like having their minds bent…

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• Physics fans and others who like having their minds bent…
• neil the wheel
Subscriber

I was looking around for an answer to the question of why the speed of light (or other massless particles) is finite. The best explanation I could find is here:
http://www.thenakedscientists.com/forum/index.php?topic=47562.0

Your question is really asking how fast a universe which lacks Newtonian time can run under Newtonian time. If you do attempt to run it under Newtonian time, you can indeed run it at any speed you like, including running through the whole of time instantly. Einstein’s model lacks Newtonian time altogether, so it also lacks speed altogether and movement too: it gives us an eternal block universe where past, present and future all simply exist as a static block. Clearly it’s difficult to think around such a model, so Newtonian time gets dragged back into it by accident whenever people try to explain how it hangs together through normal langauge, and that repeatedly introduces all manner of confusions. Many of the key words we use to describe things automatically smuggle in Newtonian time along with them, so you have to be continually on your guard.

I think what it boils down to is that light travels at the speed of time (and vice versa). The exact finite velocity is determined by the electromagnetic forces and they are what they are. If they weren’t, we probably wouldn’t be here.

Am I on the right tracks?

molgrips
Subscriber

If I knew what tracks you were talking about… ðŸ™‚

The speed of light is determined by the permittivity and permiability of free space. Why these values are non-zero I am not quite sure.

All that Einstein stuff is a consequence of the speed of light being finite, I think. As to what TIME is, that’s a whole nother question and I’m not sure it’s actually related to the speed of light.

neil the wheel
Subscriber

Well, aren’t time and space part of the same thing? Time goes slower the faster you travel and when you get toward the speed of light it tends towards 0 so that would put a limit on the speed of light!

molgrips
Subscriber

In General relativity yes, I think so, but that’s just a theory we use to describe what we see. What these things actually ARE is anyone’s guess.

Time goes slower the faster you travel and when you get toward the speed of light it tends towards 0

No, time doesn’t slow *for you*. You just look slower to everyone else.

neil the wheel
Subscriber

No, time doesn’t slow *for you*. You just look slower to everyone else.

Ooooooooooooooooooooooooooooooooooohhhhhhhhhhhhhhhhhhhhhhhhhhh Buuuuuuuuuuuuuuuuuuuuuuuuuuuuugggggggggggggggggggggggggggggggggggeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeerrrrrrrrrrrrrrrrrrr

redthunder
Member

Is this Strava time ?

molgrips
Subscriber

How could time slow for you? What would you see as slow? If time was running slowly for you then it might take a marble 5 mins to hit the floor, but your brain would be running slower too so you’d see it as the same.

Fascinating documentary on the nature of time right here

[video]http://youtu.be/NvpbW7JRu0Q[/video]

the teaboy
Member

Tenuously related and at a primary school level, but I spend far too much time just staring at this:

neil the wheel
Subscriber

Thanks sharkattack, that clears that up.

I (in my non physics way) always understood it as:

speed of particle through space plus speed of particle through time = constant.

Therefore the faster a particle travels thorough space, the slower it travels through time.

The constant happens to be 186,000 mps. I have no idea why it isn’t say, 183,000 mps or 189,00 mps,

As a photon travels through space at the speed of light, it cannot travel through time, which means, from its point of view, it similtaneously occupies every point in the universe at once.

Probably a load of bollox, but I find it quite profund.

neil the wheel
Subscriber

speed of particle through space plus speed of particle through time = constant.

Therefore the faster a particle travels thorough space, the slower it travels through time.

The constant happens to be 186,000 mps. I have no idea why it isn’t say, 183,000 mps or 189,00 mps,
Yup, that sounds like what I was thinking of. I think the value of the constant pops out of Maxwell’s laws but as you say, why it is the value it is might just be one of those things…a bit like the values of gravity or the nuclear forces. If they were different the universe would be a different place.

I’m not clever enough to understand any of this.

Why isn’t it possible to travel faster than the speed of light, supposing your car had enough theoretical horsepower?

glenh
Subscriber

Yup, that sounds like what I was thinking of. I think the value of the constant pops out of Maxwell’s laws but as you say, why it is the value it is might just be one of those things…a bit like the values of gravity or the nuclear forces. If they were different the universe would be a different place.

Exactly – it’s just the way the universe is. Different universes might have a different speed of light.
p.s. thinking about it as objects in a 4D space/time with a fixed ‘movement’ is probably a good way to go.

neil the wheel
Subscriber

Why isn’t it possible to travel faster than the speed of light, supposing your car had enough theoretical horsepower?

E=mc^2 innit? As you accelerate towards the speed of light, your mass increases to infinity and it would take an infinite amount of energy to get you beyond the speed of light.
I think..

molgrips
Subscriber

E=mc^2 innit?

No, nothing to do with that!

E being total energy. If v = c in this equation then the energy is infinite. You’d have to add an inifinite amount of energy to the thing you are trying to accelerate, which is clearly impractical at today’s energy prices.

klumpy
Member

speed of particle through space plus speed of particle through time = constant.

No. Because there is no ‘speed through space’, the speed of something is always relative to something else – and it can’t relative to space as the existence of an ether (ie: an absolute or preferred frame of reference) was disproved by Michaelson and Moreley. (Who were trying to prove the opposite at the time!)

neil the wheel
Subscriber

No, nothing to do with that!

so why does your equation have E=mc^2 in it then?

Hmmm klumpy, a veritable spanner in the works!

No. Because there is no ‘speed through space’, the speed of something is always relative to something else

speed of particle through space relative to an observer plus speed of particle through time relative to that observer = constant.

Would that work? or do you have to factor in the speed of the observer, relative to everything else?

And I know space and time are supposed to be the same thing, but I also know I experience them differently!

neil the wheel
Subscriber

And I know space and time are supposed to be the same thing, but I also know I experience them differently!

I wonder what it would feel like if we lived in 1 dimension of space and 3 of time?

waveydavey
Member

The easy(ish) way to think if it is.

Imagine you were on a clock, and if you traveled away from the clock at the speed of light.
The time on the clock would always be still. Thus time will have stopped for you, relatively speaking.

neil the wheel
Subscriber

Imagine you were on a clock, and if you traveled away from the clock at the speed of light.
The time on the clock would always be still. Thus time will have stopped for you, relatively speaking.

That’s the opposite of what molgrips said earlier.

Imagine you were on a clock, and if you traveled away from the clock at the speed of light.
The time on the clock would always be still. Thus time will have stopped for you, relatively speaking

That doesn’t work form me. It just means you are keeping pace with the photons spreading out for the clock. It doesn’t mean that time for you is passing slower, relative to the clock.

waveydavey
Member

That doesn’t work form me. It just means you are keeping pace with the photons spreading out for the clock. It doesn’t mean that time for you is passing slower, relative to the clock.

So imagine you are a photon, and you look back at the clock while travelling away, what time is it?

Time doesn’t pass for you, so in theory you don’t have time to turn and look back.

molgrips
Subscriber

The point is that nothing can travel faster than light, not even knowledge or information. So the image of the clock is basically the same as the time in that location itself, for the sake of argument!

In any case klumpy’s model would only work if two observers were moving away from each other, not towards.

Knock yourselves out:

so why does your equation have E=mc^2 in it then?
Hmmm klumpy, a veritable spanner in the works!

I wondered if someone would spot that. That’s the TOTAL energy of a body. So part of that is due to its mass, and part to its velocity (kinetic energy). That term on top has nothing to do with speed.

klumpy
Member