A few weeks ago, scientists revealed an
amazing discovery. 100 years after Albert Einstein had formulated his General
Theory of Relativity, an experiment had confirmed the existence of one of the
predictions of his theory – gravitational waves. Prof Karsten Danzmann, from
the Max Planck Institute for Gravitational Physics and Leibniz University in
Hannover, Germany said that "It is the first ever direct detection of
gravitational waves; it's the first ever direct detection of black holes and it
is a confirmation of General Relativity because the property of these black
holes agrees exactly with what Einstein predicted almost exactly 100 years
ago."
Of course, all this seems rather esoteric
to the average man, whose only recollection of Einstein is his famous equation
E = mc2 and his letter to Franklin Delano Roosevelt concerning the
atomic bomb. Few know the implications of his work, and perhaps that is why the
confirmation of his theories even a 100 years later don’t quite shake up the
world as much as it should.
And while we may wonder what effect this
could have on the average person, consider the following – in most cellphones
these days, you have a GPS transceiver. This transceiver receives precise time
signals for the up to 24 GPS satellites around earth, each with an atomic clock
accurate to 1 nanosecond (1 billionth of a second). To determine your position,
the transceiver compares the time signals from 4 different satellites, and
trilaterates your position from the time difference in the satellite signals,
and their known positions above the earth.
These satellites are 20 000 km above
the ground, orbiting the earth at 14 000 km/h. Special Relativity predicts
that due to their speed, they’ll be slower than your clock by 7 microseconds
per day. General Relativity predicts that because they’re further from a
gravitational object, they’ll be faster than our clocks by 45 microseconds per
day. For the navigational calculations to work, the clocks on all our devices
should remain accurate within 30 nanoseconds. A microsecond is 1000 times
longer than a nanosecond – if Einstein’s theories were not taken into account,
the GPS system would be inaccurate in about 2 minutes, and off by 10km in a
day.
Because E = mc2 is only the
start of the story. It is part of a solution to a paradox Einstein encountered
in formulating his Special Theory of Relativity. Einstein’s Special Theory of
Relativity was originally proposed to reconcile the Laws of Motion of Isaac
Newton with electromagnetism as described by James Clerk Maxwell.
Einstein started from the proposition the
speed of light was constant regardless of the motion of the observer, and from
that, a lot of what sounds counter-intuitive flowed. Einstein’s work on Special
Relativity showed not only that mass and energy are equivalent (E = mc2),
but also that space and time cannot be separated from one another – that time
was a dimension just like any other. From this, a few other strange features
emerged.
Since the speed of light in a vacuum had to
remain constant, something else happened when objects started travelling close
to the speed of light. In order for light observed by such an object to remain
at constant speed, time had to slow for such objects, since light could not.
This is commonly known as time dilation. And in order for the speed of light to
be constant, those observing an object travelling close to the speed of light
would see its length shorten in the direction of travel. This is called a
Lorentz contraction.
But Einstein’s Special Theory of Relativity
only explained motion in bodies without the effect of gravity, hence the term
‘special.’ Even so, up to today, it is still the most accurate model of motion
tested. But ultimately, all bodies are under the influence of gravity. And thus
Einstein worked for 8 more years, and in 1915, he published his General Theory
of Relativity.
This General Theory of Relativity combined
the Special Theory of Relativity with Newton’s Law of Universal Gravitation,
describing gravity as a property of the curvature of space and time, or
spacetime. Einstein postulated that heavy objects curved spacetime in much the
same way a heavy iron ball on a bed curves the surface of a bed. And in the
same way a smaller ball would fall into the curve created by the heavy one, so
too do all objects in space curve toward the heavier one. In fact, Einstein
showed gravity bends even light. It predicts gravitational time dilation, to
allow the speed of light to remain constant as it goes deeper into and then out
of gravity (i.e. time passes slower the stronger gravity is), it predicts
gravity can be used as a lens to focus light (gravitational lensing), it
predicts gravity can be too strong for even light to escape (black holes), and
then also predicts that when two spinning black holes collide, they’ll set off
waves in spacetime similar to the effect that waves have on a puddle if you
drop a stone in them.
This all sounds very counter intuitive,
which is why Einstein’s theories have always been the subject of extensive
testing. Thus, when on September 14, 2015 at 09:51 UTC, the Laser
Interferometer Gravitational-wave Observatory (LIGO) detectors, located in
Livingston, Louisiana, and Hanford, Washington, went off, the scientific
community cheered. Einstein’s theories had their reliability to predict
confirmed.
As our technology advances, we become more
and more dependent on them being built to model and anticipate the universe as
it is, not as one wishes it would be. The confirmation of scientific theories
not only provides us certainty about the universe we live in now, it also gives
us hope that we can find answers in the future. After all, if simple theories
on the progression of time was capable of providing us pinpoint navigation to
the entire human race a mere few decades later, who knows where this one will
take us?
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