Relativity 9 replies

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Revenge VIP Member

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#1 12 years ago

The following could be considered delving into what is commonly known as Relativity. You've probably been asked the question "If you're in a car travelling at the speed of light, then turn on the headlights, what will happen?". This is down to Relativity, and the following is my interpritation of it.

Ever heard of clocks going out of syncronisation when one is moving and one is stationary? For instance, a clock on an artificial satellite in orbit needs to be resyncronised with the standard clock on Earth once and a while because the satellite is moving relative to Earth, which appears stationary to the observer.

Astronauts who have been orbiting Earth come back to Earth younger than they would have been had they stayed on Earth for the time they were away. Fred could go into orbit for eight days, being 33 years, 290 days old when he goes. After being in space, he will be 33 years, 298 days old in Earth terms (using our calendar system), but the time his body has measured from his birth to the current point in time would be less than the amount of time in 33 years, 298 days.

They say this is because time slows down for the moving clock and the astronaut and any other particle (or collection thereof). But how can this be? A digital clock on a satellite ticks at exact intervals because a fixed charge will build up in a capacitor (a battery which discharges itself after a certain charge is reached) and then send an electromagnetic (EM) pulse to a processor which increments the time. Won't these intervals be the same as on Earth? Don't EM waves all travel at the universal constant (what is commonly termed as the speed of light), therefore meaning that a clock will tick at exactly the same speed on Earth as in orbit of Earth?

The explaination, sadly, is even more complex than the problem, and understanding it is easier if you've done Mathematics to a high level. This so-called slowdown in time is encompassed in what Physicists call Relativity. You've probably heard of Einstein's Theory of Relativity - this is mostly his work.

Let's take a car travelling at 30 miles per hour as an example. To a man standing stationary on one side of the road, the car drives past and appears to be going at 30 miles per hour. Since the man is stationary - in other words, travelling at 0 miles per hour - the car will be travelling at 30 miles per hour relative to his own speed. However, to a man running next to the car in the same direction at 10 miles per hour, the car will appear to be going 20 miles per hour faster than he is going. To each observer, the car is going at a different speed from their viewpoints.

However, the car is nevertheless still travelling at an absolute speed of 30 miles per hour. If we then take the car and say it is travelling at the speed of light (dispite that being impossible, but it helps when trying to visualise things), and the runner running at the same proportion speed as before (in this case 1/3 of the speed of light) and the observer still standing still, then the same thing happens - the car appears to be travelling at the speed of light to the stationary man, while it appears to be going at 2/3 the speed of light to the running man. The car is moving slower to the running man than to the stationary man - speed, and hence time (because speed and time are related), has slowed down for the running man.

The same can be applied to anything - the thing for which time has slowed down for does not need to have a brain, it does not need to know time has slowed down for it, but it still experiences the change. Therefore the satellite with the clock going out of sync can be explained with relativity, because all EM waves travel at the speed of light, which is dependant on the speed of time.

I just thought I'd share with you this fascinating stuff. Hope you've learnt something, and if you think I'm wrong, feel free to say so because this is in no way a professional's view. Now who wants to give the question about the headlights a shot?

Note from Reven:

That, my chums, is Physics. Chemistry is a subset of Physics, and Biology isn't a real science. No denying it. Bow down to Physics.




Reno

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#2 12 years ago

Yeah Taylor (Charlton Heston) from the Planet of the Apes knows this better than anyone.




Guest

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#3 12 years ago

Amen to that Reven.




Jackthehammer

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#4 12 years ago

Time is relative to the observer :)

Nothing will happen when you switch the headlights on ;) And by nothing, I mean theyll just switch on, like normal.




Nemmerle Forum Mod

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#5 12 years ago

Nothing will happen when you turn the headlights on since it would take an eternity for the energy to go from the battery to the lights.




Chemix2

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#6 12 years ago

Light is a particle, represented commonly as a wave, like any particle could be represented, it has mass and size and is the result of two electrons colliding. It has a specific speed at which it travels which as far as I see it, means nothing to any object than itself, thus I see no real reason why the speed of light would be the end all speed for all matter and energy in the universe. A photon, or particle of light, travels at it's speed because of it's lack of mass (and therefore lack of wheight, though it does have both albeit in extremely small ammounts, otherwise it would be unnafected by blackholes or gravity of any sort which it is) and the kinetic energy exerted upon it by the release of energy during an electron collision. Part of the electrons becomes energy and the other part becomes a photon if I remember correctly.

Time as we know it is relative to gravity, time goes faster for those in space than it does on Earth because of the lack of gravity in space in comparison to it's strength nearer to the center of the Earth (where we are). It's rather slight and unnoticable because Earth has so little gravity in the grand scheme of things.




Revenge VIP Member

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#7 12 years ago

Einstein also happened to explain the Photoelectric effect, among other things, which explains how light gets its energy. It's to do with electrons and their discreet energy levels, but I can't remember all of it.




Jackthehammer

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#8 12 years ago

Reven! you disappoint me! :eek:

:p You should have a drink with Riles sometime, I'm sure you'll have an interesting conversation ;)




Aeroflot

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#9 12 years ago

jackthehammer;3269760Reven! you disappoint me! :eek:

:p You should have a drink with Riles sometime, I'm sure you'll have an interesting conversation ;)

That's stuff you learn in high school. :lookaround:




Revenge VIP Member

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#10 12 years ago

I did Physics to Higher level (A-Level, basically) last year but I didn't do Advanced Higher this year (first year university standard) because the subject clashed with Advanced Higher Computing. What I learnt about Relativity was mostly from Wikipedia and Steven Hawkin's book, A Short History of Time.