Why does
E=Mc
2
?
It's a familiar equation that saw Albert Einstein
bridge the gap between mass and energy,
revolutionising physics in the process
ne of the most famous equations
in the history of science is Albert
Einstein's equation, E=mc², published
in 1905, the year known as Einstein's
‘annusmirabilis’. In this work Einstein established
theequivalence between mass and energy, two
concepts disconnected until then. In such a simple
and beautiful way, the theory of special relativity
governing space, time, matter and energy came to
be. In the subsequent decade Einstein expanded his
theory to include gravity, thereby creating the theory
of general relativity. Both theories are essential for
the functionality of a lot of modern technology, for
instance GPS navigation systems, without which we
could not even dream of self-driving cars.
This simple yet fundamental equation involves
only three quantities: energy, E; mass, m, and the
vacuum speed of light, c. It tells us that mass may be
converted into energy, more specifically that a given
process involving just a tiny bit of mass may lead
to the release of an enormous amount of energy.
An example of the process occurring in nature is
electron-positron annihilation, where an electron
and its antiparticle, the positron, may interact,
leading to their disappearance and the appearance
of two high-energy gamma-ray photons: production
of light from matter. Perhaps more surprising, this
equation also implies that it is
possible to produce mass from
energy. For example, two photons,
which are massless, with sufficient
energy may interact and create an
electron-positron pair: production
of matter from light. Another
example of this relation between
mass and energy is the creation of
helium from two hydrogen atoms,
and a fraction of the hydrogen
mass is radiated into energy in
this fusion process. This is the
underlying physics that allows
stars to shine and remain stable
for long periods of time. We can
thus witness the effects of E=mc²
everyday by noting the light from
our Sun and watching the starry
sky during the night.
Instant expert
O
BIO
Dr Alberto
Domínguez
Domínguez is
an astrophysicist in
the High Energy Group
(GAE) of the Universidad
Complutense de Madrid,
Spain. His main area of
research is understanding
the most energetic regions
of the cosmos, particularly
gamma rays. But this
knowledge of ‘energy’
stems from the century-old
theories of Albert Einstein.Energy,E
Everythinghas– orhasthe
potentialtobe– energy.Thatisa
fact.Eventhepensittingonyour
deskhasenergyassociatedwith
it,andthisisinferredbyEinstein’s
mostfamousequation.More
specifically,a processinvolvingjust
a tinybitofmassmayleadtothe
releaseofanenormousamountof
energygiventheverylargevalue
ofthesquareofthespeedoflight.