Speed Limits

The best description I've ever seen of the speed of light comes from "The Elegant Universe" by Brian Greene. I'll have to paraphrase because I don't have the book here, but the basic idea was this:

Everything in the universe is always travelling at the speed of light, but the "movement" is occurring in the time dimension(s) as well.

Simplifying to two spatial dimensions and one time dimension gives a great visual analogue for the idea. Your movement through time/space is a vector with length "c" that is centred at the origin and points in your direction of motion. The projection of this vector onto the spatial plane is your rate of movement in space, and the projection of this vector onto the time line is your movement in time! As you approach the speed of light in the spatial plane, you can see that the projection of the vector onto the time line gets smaller and smaller, meaning time slows down for you. When viewed this way, the speed of light isn't really a "speed limit", more of a "speed imperative". 😉

Of course, this brings up other questions like "what happens if we swing the vector past the spatial plane into the region where time is negative?". I don't have the answer, but I believe the reason why this can't be has to do with entropy (which directs time's arrow), and energy (the required amount of which increases exponentially as you try and divert the vector closer and closer to pure spatial travel).

A question about the speed of light came up in my S.S. class recently. The question was "Has the speed of light always been what it is calculated as today?" I never considered this--I just assumed that it was a constant, never-changing thing. But I suppose there's no reason for me to assume that. Could light have travelled faster--or slower---in the distant past?

Originally posted by PBE6
The best description I've ever seen of the speed of light comes from "The Elegant Universe" by Brian Greene. I'll have to paraphrase because I don't have the book here, but the basic idea was this:

Everything in the universe is always travelling at the speed of light, but the "movement" is occurring in the time dimension(s) as well.

Simplifying to ...[text shortened]... y as you try and divert the vector closer and closer to pure spatial travel).

Yes, I remember reading that as well. It made a lot of sense to me. I'm surprised it isn't more widely used. However I still do wonder why there needs to be a maximum vector length.

Originally posted by ark13
Yes, I remember reading that as well. It made a lot of sense to me. I'm surprised it isn't more widely used. However I still do wonder why there needs to be a maximum vector length.

Not maximum. Fixed, sounds like. Speed is determined by the angle of the vector, not the length of it.

If you varied the length of the vector, you would change the rate of time change when at rest as well as the speed of light I think.

http://www.space.com/businesstechnology/080813-tw-warp-speed.html

Originally posted by PinkFloyd
A question about the speed of light came up in my S.S. class recently. The question was "Has the speed of light always been what it is calculated as today?" I never considered this--I just assumed that it was a constant, never-changing thing. But I suppose there's no reason for me to assume that. Could light have travelled faster--or slower---in the distant past?

That is one of the theories floating around about how to eliminate the need for the inflationary period of the universe, that light moved a LOT faster near the BB than it does today. Mostly the evidence shows no such thing.

The famous "double-slit" physics experiment was on the Disc. channel again last night. I still don't grasp it's importance completely, but the narrator claimed that this "proved" that something (a photon) could be in 2 places at the same time--and in 2 times at the same place. Aside from the seeming mumbo-jumbo there, and to get back to the speed of light issue--if it takes energy to get something to move, and more energy to make it move faster, suppose we could create a teeny-weeny ramjet and strap it to a teeny weeny photon. Wouldn't that theoretically make light go faster-than-light?

Originally posted by PinkFloyd
Aside from the seeming mumbo-jumbo there, and to get back to the speed of light issue--if it takes energy to get something to move, and more energy to make it move faster, suppose we could create a teeny-weeny ramjet and strap it to a teeny weeny photon. Wouldn't that theoretically make light go faster-than-light?

There are some technical/practical problems with your idea.

First, the Newtons action/reaction law.
Second, if the teeny-weeny ramjet have zero mass, then you cannot get *this* into the speed of light.
Thridly, light has only one speed in vacuum, and one speed only, and that is (you guessed it) speed of light. Light cannot go faster than light.

Nothing with mass cannot go in the speed of light, but if the particle is born in a supralight velocity, it can thrive there pretty well. The funny thing is then that it takes energy to slow it dowsn, and if you don't do anything about it, it wants to accelerate to an infinite velocity (= lower energy).
But mass *in* the speed of light - impossible.

Originally posted by FabianFnas
There are some technical/practical problems with your idea.

First, the Newtons action/reaction law.
Second, if the teeny-weeny ramjet have zero mass, then you cannot get *this* into the speed of light.
Thridly, light has only one speed in vacuum, and one speed only, and that is (you guessed it) speed of light. Light cannot go faster than light.

No ...[text shortened]... erate to an infinite velocity (= lower energy).
But mass *in* the speed of light - impossible.

I knew there was a flaw in my logic somewhere 😉