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Q&A: General Astronomy and Space Science
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Q:
Someone once said : "Time and space are modes by which we think
and not a condition in which we live." I did not get exactly
what it meant. Can you help me?
A:
Albert Einstein (Credit: Caltech)
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Maybe what was meant was that since Albert Einstein's work on
the nature of space and time, we realize that the two are not
independent. There is no such thing as absolute space and
time.
It is impossible to say that two things happen at the same
time. It depends on the motion of the observer. For example,
suppose you were standing in your room and saw two distant
flares go off at the same time, one in the southwest, and one in
the northwest. A pilot flying from south to north in a
supersonic aircraft would see the two flares, too, but because
he is moving toward the flare in the northwest, then the light
from it would reach him a fraction of a second before the light
from the flare in the southwest. This effect has strange
consequences for speeds close to the speed of light. Particles
that are known to have a lifetime of two micro-seconds when they
are at rest appear to have lifetimes of 100 micro-seconds when
they are moving at speeds very close to the speed of light. The
same thing would happen to us if we could move close to the
speed of light. We would think we were living a normal life, but
a person on Earth would think we were living much longer than
normal. The same holds for the length of an object. Its length
depends on the speed at which it is moving relative to the
measuring device. Fortunately we can work it all out with the
formulas given by Einstein's theory.
So, we don't live in just space or time, but in space-time.
Here is a quote from Hermann Minkowski, one of Einstein's
professors who once called Albert "a lazy dog", but later became
famous for working on Einstein's theory of relativity:
"Henceforth space by itself, and time by itself, are doomed to
fade away into mere shadows, and only a kind of union of the two
will preserve an independent reality."
Strong gravitational fields, like those thought to exist around
black holes, can also warp space and time and cause even weirder
effects, but that is another story.
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