The speed of light... Much of the science based around the speed of light is thanks to Einstein.
e=mc2, for example, energy is equal to mass times the square of
the speed of light in a vacuum (c stands for 'constant', here).
An interesting point about that - if 'c' is a constant, 'c2' is also a constant. So the equation would be less misleading if it read "e=mc". After much thought on the subject, I consider that it is for clarity that the number is squared.
Presumably there has been some derivation through what are accepted to be the three measures, distance, time and mass. Speed being distance/time, that would mean energy is measured in (mass * (distance/time)2), which would be kgm2s-2. (kilogram metres squared per second squared). I don't know if that's what a Joule is, and don't feel like looking it up. If it's not then there's something even more dodgy in Physics than I thought.
On to the next dodgy point, relativity. Time is relative, says Einstein. Motion is relative, says Newton. Both are accepted as fact.
Time being relative to motion is Einstein's point; as one approaches the speed of light, time slows down. If one could exceed the speed of light (which it is usually assumed one can't) they would go backwards in time. The catch is, apparently, that if one were to travel at the speed of light away from Earth for a light year, then back again, the time on your watch would match the time on Earth because your travel has been accelerated out and decelerated in (or some such). However (this bit makes no sense to me), it is also said that if one flew in a circle at the speed of light, the clock you have would not match the stationary clock on Earth, but be a short time behind.
Accepting this as fact, for no good reason but argument, I then go on to apply Newton. Motion is relative. So, as far as the moving clock is concerned, it was the other clock that was moving. So it's the other clock that's a short time behind.
So, what's going on here? Clock A looks at clock B and says "You're two seconds behind, mate."
Clock B looks at clock A and says "Nonsense, you're the one that's two seconds behind."
I think not.
People have suggested to me that it's because of acceleration. This doesn't help at all - acceleration being a motion/time comparison, and motion being relative, clock A says clock B is accelerating, and vice versa, just as with moving.
How to explain this discrepancy? I have two ideas. Reject the time is relative proposal (which at face value looks to be the less likely), or reject the motion is relative proposal. If one were to do the latter, then motion needs something to be compared against. A control, as it were. (Cross reference : Aether)
The argument in favour of this is that if one were to reject relative time, travelling faster than the speed of light would be possible. Consider in relative motion without time dilation, object A travels west at two thirds of the speed of light, while object B travels east likewise. Relative to each other they would be travelling at one-and-a-half times the speed of light.
How about if it were possible to travel faster than the speed of light, and time dilation occurs, such that one goes back in time? Paradox becomes the order of the day, what happens if I go back and stop myself building the time machine? What happens if I go back and stop myself being born? The whole idea of time travel is preposterous unless there's some way to sort this out. Two ways spring to mind for me. Multiple time lines, as explored vaguely in Back To The Future 2, meaning that all you do is create or travel to a different branch of the 'universe' (Cross reference : Multiverse), or linear fourth-dimensional predestination-filled time, wherein you obviously can't go back and stop yourself being born because you didn't. Whatever you might try won't work, and you know this because it didn't work, because you were born. You can go back and affect things, but you can't change things. Any changes you make go to make the world the way it already is.
On to another tack, along the same lines. If time is a fourth dimension, what amount of time is the equivalent of a metre? Picture some primitive four-dimensional shapes... How about the pyrasphere, a sphere that shrinks slowly into nothing. I think of this being to a cone what a pyramid is to a square. Try to picture it with the fourth dimension being something other than time. Just another form of distance. If you can see that then you should be able to manage to ponder a five-dimensional shape. Get the pyrasphere and shrink it. About there it starts to get tricky to picture, for me. With a little effort I can go as far as imagining a six-dimensional form without using time.
If you managed the relatively simple task of imagining the pyrasphere using time as your fourth dimension, try rotating it ninety degrees through the dimensions. Time becomes up, up becomes right, right becomes back and back becomes time. What does the pyrasphere look like now? Tricky, isn't it? I may write a program to do such tranformations, because I'd like to see a person moving the wrong way through the dimensions.
Ah well... I'd write more, but I haven't got time.
[ Think back... ]
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