28. Spacetime and the Doppler effect ---------------------------------------- Previous - Next - Contents
The description of spacetime being like a block of ice (as I
outlined yesterday) would
perhaps reinforce a religious person (who believes in a Personal God)
in his belief in Predestination, or a non religious one in a degree
of so called determinism.
Writing yesterday's story
about John, Pete and Max, the Doppler effect suddenly came to mind. I am sure you
are familiar with it. Say you are standing along the road while a car
is approaching. Its speed towards you changes the wavelength and
frequency from its engine noise (to YOUR ears) to a higher than its actual pitch.
Then, as soon as the car passes you, its pitch instantly drops (again to your ears' perception) as it
moves away from you.
Astronomers use the Doppler effect to determine
the speed and direction of stars and large glowing meteorites. When its
observed light moves towards the (low frequency) red of the spectrum
(a so called "red shift") it reveals that the star is moving away from us. If on the other
hand the light is shifted to the (higher frequence) blue of the
spectrum (a so called "blue shift") the object is moving towards us.
As a layman I see a resemblance of (sort of) a Doppler effect in
spacetime. On the diagram below, Pete is moving towards me at high
speed from my distant future. As Pete moves closer he traverses ever
(for me) closer future points. For an instant he joins my NOW slice,
then moves away deeper into my past.
Pete, throughout his travel remains in his own NOW slices, but from my
perspective he moves from my high frequency (?) future into my lower
frequency (?) past. Just like a Doppler effect. Interesting ? Space and time as we understand them now are closely interrelated, and combined into one single entity : spacetime, which is not "absolute" (fixed) but flexible and can buckle, stretch, contract, bend under the influence of gravity or energy. As Einstein put it :
Einstein's publication of his Theory of General Relativity in 1916 put the sciences of physics and cosmology on an entirely new path of discoveries, uncovering amazing aspects of reality, which are hard or even impossible to comprehend by the limited human mind. Brian Greene in his book Fabric of the Cosmos (I have referred to previously) has documented much of this, explaining it in easy to understand common layman's language. Here follows his visualisation of time.
Time is not like a dynamic flowing river, rather it is like a frozen
block of ice. Consider an elongated block of ice, cut in parallel
slices like a loaf of bread. Each slice represents a "NOW"
moment in your life. And of course as your notion of time progresses
you proceed from one "NOW" slice to the next, and the next, and so on.
On the Diagram below your past is shown in purple. The thin dark purple
lines are "NOW" slices you lived through moments ago. The thick purple
line is you NOW point right now, while the pink future is ahead of
you.
John, who was with you talking to you a minute ago, steps into his car
and drives away from you. As an immediate result his NOW time
slices are rotated at a small angle to yours, cutting through your
past. It is important to realise that this is not just theory. It has been proven with high precision clocks in airplanes flying around the world. The larger the speed difference between the two people the larger will be the angle between their two sets of NOW slices. And the farther away the two people are from each other the deeper they cut into each others past or future.
Here on earth the differences are minute and not noticeable in daily
life. Modern planes however do take the above into account with respect
to their flight navigation.
Do the same imaginary exercise while Max is sitting in an airplane and
the NOW time slice difference has increased to a wacking 10,000 years
!!
Copyright © 2010 Michael Furstner
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