Page 22 - All About Space 68 - 2017 UK

Mirror universe
Mirror
universe

An alternative universe would have erupted from
the Big Bang, almost 14 billion years ago

Could we ever see into this other region, witness Think of inflation as expansion on steroids. It says
time running backwards, and see how the two the region we now see as our universe swelled in size Evidence for a
compare? “We have about as much chance of seeing from smaller than an atom to the size of a grapefruit
what happens there as we have sending a message in a trillionth of a trillionth of a trillionth of a second. mirror universe
back in time to tell people to vote a different way in What we know as the Big Bang – the beginning of
the Brexit election,” says Hartle. For them to send a time in our universe – happened at the end of this
message to our future, they'd need to send it back process after space had grown by a tredecillion (that's Quantum gravity
through their past to cross the Janus point, and vice ten followed by 78 zeros!). This inflationary period Reversed time arrows
versa. To compound the problem, the concepts of helps explain the variations in the CMB. Natural appear in some models,
which try to explain the
space and time break down in the transition region quantum fluctuations were blown up so rapidly Big Bang in terms of
between the two. that they became set in, leading to slightly hotter
quantum gravity
But that doesn't stop the evidence stacking up and colder spots in the juvenille universe. Such a
that another universe with its time reversed could rapid growth spurt would also have ironed out any
be a real possibility. It also crops up when poking curvature our locallregion of the universe had, Time reversibility
holes in the Big Bang theory. The Big Bang theory is and quickly separated areas that were originally of physical laws
© Mark Garlick/Science Photo Library, Moonrunner Design LTD Cosmic Microwave Background (CMB). However, caused it to happen in the first place. The most likely – don't care which way
a great one – among other things, it explains why the
causally connected.
We know that some laws
So far, so good. But the catch is that, if inflation is
of physics – including
universe is expanding, why its composition is largely
Newton's Laws of Motion
75% hydrogen and 25% helium, and why we see a
to be believed, you need to find a mechanism that
time runs.
cause suggests it doesn't just happen once – multiple
there are some things the simple Big Bang model
regions are constantly inflating to create multiple
alone cannot explain – such as the tiny temperature
Inflationary era
universes, in a process known as eternal inflation.
variations in the CMB. It also cannot explain why the
Inflation best explains
If there are enough of these other universes then it
curvature of the visible universe appears flat, or
the birth of our universe,
how two distant parts of the universe can be
is statistically likely, if not certain, that somewhere
and it implies there
out there in the multiverse there are copies of you
causally connected. So, in the early 1980s,
are probably multiple
physicists, including Alan Guth at the Massachusetts
reading copies of this article.
universes, each with
Institute of Technology (MIT), came up with a
More recently, Guth has been working with
solution called inflation.
22 cosmologist Sean Carroll from the California Institute different physics.