1. The speed of travel, light and time
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Today something completely different for a change.
I try to be informed about the current discoveries in modern physics and
cosmology. I find it important to have a greater awareness of the Universe
in which we live and my own personal place within it. "Try" I say, but that
is not so easy. I have struggled through a number of books in the past and
although they have given me some ideas, it has never provided me with the
clear insight I am searching for.
Last year however I got hold of a great
book by Brian Greene called "The Fabric of the
Cosmos". I am only halfway through it and also need to go through it
once more to firm up my understanding, but it is easy to read and it is
giving me great insights.
Let me try to explain to you for example Einstein's basic concepts of
time and space time. Here we go.
Say you have a good friend with the police (always good to have) who is
willing to lend you his radar speed gun. With this hot little instrument you
step into your car, drive to the nearest highway and get out.
your speed gun at that vintage car on your right, and measure its speed.
That is right, it is coming towards you at 100 kilometers per hour
That was a piece of cake, wasn't it ?
Now get into your car and drive
towards it at 50 kph and measure that vintage's car speed again.
still drives towards you at 100 kph and you drive towards it at 50kph, you
are getting closer to each other at a speed of 100 + 50 = 150 kph. Agree ?
The radar gun definitely says so !
You get out of your car again and this time point your speed gun at an
un coming particle of light ("photon"), from the sun, the moon, a street
light, does not matter.
Wow ! That is coming at you fast, at somewhere
around 300,000 km per second. In physics this speed (speed of light)
is represented by the letter c.
You are very well connected and also happen to have a friend in the Air
force who is willing to take you on a joy ride on the latest jet fighter
they are just testing. Crammed in your seat you aim your speed gun through
the windscreen again at an incoming photon as you fly towards the sun. What
happens ? Is this gun not working properly ?, You shake it, bang it against
the windscreen, try again. The same reading again. It has not changed from
when you were standing still on the ground.
You would think that 4,000 kph in this jet should make a difference. But it
does not. No matter how fast you fly, or in what direction, the speed gun
will always show the same speed, c.
This was the great puzzle facing scientists around 1900. No one could figure
it out. So Albert Einstein, an unknown clerk in a Government office, set his
mind to it. The answer he came up with has changed the way we look at the
world forever !
And it is so simple. A speed is a distance (in kms) divided by a time unit
(1 hour or 1 second). Einstein did not (like everybody else) look at the
distance part of the equation, but instead at the time unit and came
to the startling conclusion that when you traveled at increasing speed
through space the time unit (second) would stretch, become longer !!
other words the faster you move the more time slows down. You
can keep increasing your speed, but not infinitely, because when you reach
the speed of light time actually stands still altogether.
startling fact has been confirmed as correct by numerous subsequent
Time is not absolute, fixed and independent, but instead
flexible and an extra dimension added to the three dimensions of space. It
is part of what is now called space time.
But wait (as the TV adman says), there is more !!
You, me, we all travel at the speed of light. Not through space, but through
space time. Here is how it works.
Say you want to travel to a place which is 500 km
exactly due North of where you start of from. So you get into your car, get
up to speed and set your cruise control on 100 kph. As long as the road you
travel on is heading due North you will approach your destination at 100
But as soon as the road turns say to the North East things change.
You still travel on it at 100 kph, but only part of the speed is getting you
North, the other part is moving you to the East. As the Diagram below on the
left shows you now approach your North target at the speed of around 70 kph.
The same thing happens in space time.
Uncle Jo above, quietly sitting in his dinghy waiting for the fish to bite,
is blissfully unaware that he is traveling through time at close to the
speed of light (remember : the earth is moving through the universe,
therefore so is Jo). The hungry fish darting backwards and forwards underneath
his boat is on a slightly slower time setting. Just as well because if it
does go for Jo's lure there may be little time left for it no matter how
long time is stretched.
The passengers in the plane going overhead are on a
slower time scale yet. And for the light particles coming from the sun
bouncing on Jo's bald head the time is standing still altogether.
Isn't this an amazing scenario ? Have you ever thought about life around you
in this way ?
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Copyright © 2010 Michael Furstner