On the Coast – Over 55 Issue 28 I March/April 2019 | Page 28

General
Relativity
by David Fletcher
I
t was 100 years ago in 1919,
that Albert Einstein got
divorced and then became a
worldwide celebrity. Happily,
there was no correlation
between these two events,
but let’s look at what caused
Einstein’s sudden rise to fame.
photoelectric effect (for which he won the
Nobel Prize and which also was an
important milestone in the burgeoning
theory of Quantum Mechanics) and of
course, his theory on Special Relativity,
which soon gave rise to an additional
thought where Einstein postulated that
mass and energy were equivalent (e=mc2).
All these works were enough to give
Einstein ‘proper’ physics jobs in German
Universities where he was allowed to
develop a totally new theory of gravity
known as General Relativity (GR). [1]
Notoriously difficult to explain, GR is
usually given just a passing paragraph
in non-specific physics texts, which
are often coupled with a picture of a
ball sitting on a 2-D line graph bending
around it. Culminating in an equation
(known as the Einstein Equation) that
involves tensor mathematics, differential
geometry, spacetime metrics and a
cosmological constant, it is not surprising
that introductions to the topic invariably
get a little poetic. In that vein there is
perhaps none more succinct a description
of GR than given by the physicist John
Wheeler, “Spacetime tells matter how
to move; matter tells spacetime how to
curve.” [2]
Our Moon is of such a size and orbital
distance that when it passes perfectly
between us and the Sun it blocks out
almost all visible sunlight and the
phenomenon is known as a Total Solar
Eclipse. This kind of event is not too
frequent as the Moon orbits the Earth at a
slightly more tilted angle than the Earth’s
orbit around the Sun.
You may recall in August 2017 a
certain president, against all
recommendations, decided to look
directly at an eclipse as the Moon
traversed North America. Although it is
not advisable to gaze upon a solar eclipse
without proper eye protection, it is a
perfect opportunity for astronomers to
observe objects that are normally
overwhelmed by our Sun’s intensity. In
May 1919 two expeditions took advantage
of an eclipse to measure whether or not
light from distant stars
appeared to bend as it passed
close to our Sun on its path to
Earth. The confirmation that
this light did bend was the
second proof that Einstein’s
new theory of General
Relativity was holding fast.
The general public learnt the
name, Albert Einstein, as
1919 excerpts from the New York Times
newspapers in London and
New York exclaimed,
“Revolution in Science” and “Einstein
One hundred years on from the
Theory Triumphs.” [1]
initial tests of GR there are many more
confirmations that Einstein’s theory of
Whilst working in Switzerland as a
curvy spacetime, due to the stuff in it, is
patent clerk, Einstein had developed and
the best model we have to explain gravity
published many pivotal physics theories.
and its effects. The Global Positioning
Amongst these was a theory on the
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S EN I O R S O N T H E C OAS T
72-year-old Albert Einstein – photograph by
Arthur Sasse https://allthatsinteresting.com/
albert-einstein-tongue-photo
System would quickly become wildly
inaccurate were it not for corrections
governed by GR. [3]
But in spite of its success, no one
has yet reconciled gravity with the
incredibly successful theory of Quantum
Mechanics. With modern scientists
exploring frontier areas, such as Loop
Quantum Gravity and String Theory,
perhaps one day soon we will see,
“Revolution in Science,” declared again. [4]
REFERENCES
[1] Kumar 2008, Quantum, Icon Books
[2] Wheeler 1998, Geons, Black Holes
and Quantum Foam, W.W. Norton and
Company
[3] Zee 2013, Einstein Gravity in a Nutshell,
Princeton University Press
[4] h
 ttps://www.preposterousuniverse.
com/podcast/2018/10/15/episode-18-
clifford-johnson-on-whats-so-great-
about-superstring-theory/ (website
visited 21-12-2018), Sean Carroll
David Fletcher is a 45 year old undergraduate of
Physics at Macquarie University.
twitter contact @phys_fletcher