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Imaginary experiments seem more than a little odd.
Could human imagination really mimic the thoughts of God?
Could little fantasies of mathematical laws by human mind conceived
tell the truth of Reality well enough to be believed?
We answer that silly question with an example shining bright;
a phenomenon deduced from a simple effect – the force exerted by light.
A tight, narrow beam of light comes streaming out of its source
and upon the lamp it exerts a faint and steady force.
A flashlight or a lamp that is plugged into a socket
are what science-fiction fans call a photon rocket.
Take two tight-beam lamps and place them back to back
and mount them on a carriage on a straight railroad track.
Jack sits on the moving carriage and measures out what counts;
the lamps’ light comes out yellow in precisely equal amounts.
To Jill, sitting by the track, that description’s just not true:
the rear beam has turned red for her and the forward beam is blue.
What Jill is seeing in the light is the relativistic Doppler shift
and from our understanding it we gain a wonderful gift.
The difference between the beams exerts a strange and spooky force.
It doesn’t cause acceleration, yet it pushes on its source.
The rocket equation has two terms, this we all know;
mass times acceleration and velocity times flow.
The second term is strange to us; it doesn’t seem quite right.
And yet it tells us something important about the force exerted by light.
It tells us that mass is energy and that energy has mass;
and that from one into the other, occasionally they pass.
So now mass becomes energy in one fixed proportion,
wrought from inert matter by nuclear distortion.
From pure imagination we have gained a gift so rare.
As Einstein put it so elegantly, "Ee equals em cee square."
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