Relativity can make simple things remarkably complicated.
Even as straightforward a question as, ‘How far away is dinner?’ takes on added and problematical dimensions.
The theory of relativity is basically a thought-experiment dreamt up by Albert Einstein. As a description of the fundamental conditions of the Universe it can’t be directly tested, but its effects can be observed, and have been.
The theory is based on two ideas.
First, that the descriptions of how physical things work and interact in the Universe – the Laws of Physics – have the same effects for everyone occupying an equivalent frame of reference. To get your head around this, imagine taking a trip on a train: all the windows are blacked out, and the train travels at a constant speed, in the same direction, and it is all perfectly silent and smooth (ok, only the first condition ever has the slightest chance of being satisfied).
You are, in fact, moving. But everything you can observe is moving along with you at the same rate. In a situation like this you would have no sense of motion, and no way of measuring if you are moving. The train carriage would be your frame of reference.
Different effects would be observed in a train driven by a maniac. Wild acceleration, or spinning around would create motion within the frame of reference – and may induce vomiting.
The technical terminology is an ‘inertial reference frame’ or objects in ‘uniform motion’.
We rely on uniform motion all the time. Every time you drop an Anvil on the head of an enemy, you are tacitly operating on the belief that the Anvil will descend in an orderly and uniform manner.
And all other things being equal, the Anvil does behave in a decently anvillian fashion and come crashing down.
It does this despite the fact that You, the Anvil, and the Enemy, are all whizzing through space at roughly 107,156 km/h.
Breathtaking…
The second idea, and this might seem weird, is that the speed of light doesn’t change.
Don’t argue, it just doesn’t.
Not even orange traffic lights.
The speed of light (in a vacuum) is a constant for all observers, regardless of how they are jiggling about themselves, and regardless of how the light-source is moving.
This contrasts with other objects in the Universe. If I was to throw a Tortoise at you while we were both standing stationary beside the road, the Tortoise would travel at the same speed away from me, as it would be approaching you. The Tortoise would depart my hurling arm at 150km/h (a man can dream), traveling away from me at that speed. And the same Tortoise would approach your Erstwhile Unsuspectingness at precisely the same speed.
However, if you got wind of my cunning plan, and took off like a fleet-footed Achilles, the Tortoise would still depart from me at 150km/h but it would approach you at a relatively slower speed. Assuming a serious turn of pace, say 50km/h – then the Tortoise is only catching up to you at 100km/h.
You see, the speed of the Tortoise is relative to our own motion.
This is exactly NOT what happens with light. It goes at the same speed for all of us, even when I’m standing still and you’re running away. Even if I’m bareback riding a Tortoise and you have bionic legs and can run at 150km/h.
Light is a constant speed and would appear to be the same for both of us, regardless of our own movement.
This has all manner of interesting and humorous effects:
We all know that two Tortoises both traveling at 50km/h would have a combined speed of 100km/h if they were to collide head on. Their speed relative to each other is double their speed compared to a stationary observer.
But the closer you get to the speed of light the more this doesn’t apply.
Two Tortoises traveling towards each other at 90% of the speed of light (from a 3rd party point of view) do not meet head on at 180% of the speed of light. In fact, they meet at a leisurely 99% S.O.L..
Surprised?
Not more than the Tortoises, I can tell you…
It doesn’t matter what all the other objects in space are doing, light just gets on with the job. It is a constant. The speed of light is the speed limit for everything in the Universe.
And considering that the speed of light is 1,079,252,848.8 km/h, I personally think this is quite generous.
The other famous, and bizarre effect is Time Dilation:
If you imagine two clocks – one stationary, and the other moving (really fast).
If you positioned yourself next to the stationary clock, and watched the moving clock very closely (and had pretty remarkable vision), you would appear to see that the time showing on the moving clock ticks by slower than on the stationary clock.
It’s because of the speed limit on light.
Because light is moving at a constant speed, as the clock moves away it takes the light a little bit longer to reach me. So the little bit of light carrying the tick of the clock takes a little bit longer to travel the distance, and then a little bit longer, and so on. As long as the clock keeps moving away, its time will appear to slow down.
All of this has unforeseen consequences for Dinner.
How far away Dinner is, in terms of space, has a very real bearing on how far in terms of Time.
If your dinner happens to be a Tortoise, who isn’t demonstrating much personal commitment to The Cause – then the rapidly increasing Space between Oneself and One’s Dinner can lead to dramatic Time Dilation.
Dinner may be Late.