24 | New Scientist | 30 November 2019
T
HERE may not have been
a beginning to the thing
we understand as
“the universe”. Before I explain
what I mean, I should say:
of course, this isn’t the story
I expected to tell audiences
when I was a child who wanted
to be just like Stephen Hawking.
I was certain, in fact, that the job
I was signing up for was the one
where we figured out exactly what
happened in the very beginning,
to a level of detail that humanity
has never before known. As a
grown-up scientist, I have had
the wonderful opportunity to
investigate that era and to
discover again and again that
the universe is more bizarre
than we previously imagined.
The old story from 1980 or so
goes that in the beginning of space
and time, space-time exploded
out of nothing and then rapidly
expanded. The expansion was
so fast that it grew faster than the
speed of light, because it turns
out that the only thing that can
violate the universal speed limit
is space-time itself. This era,
known as inflation, was first
simultaneously hypothesised
by Alan Guth, Alexei Starobinsky,
Andrei Linde and a team
comprised of Martin Einhorn
and Katsuhiko Sato. They were
all motivated by a desire to try
to explain phenomena that
astronomers had observed.
Before we even try to imagine
what inflation means, we have
to grapple with the expansion of
space-time and what space-time
even is.
The idea that space and time
aren’t completely separate entities
is a relatively new one. Their
merger is a theoretical necessity
induced by Albert Einstein’s
relativity, which tells us that when
two of us are moving with respect
to each other, your space and mytime can mix: time and space
aren’t as independent as they
feel on everyday, human scales.
The expansion of space-time
itself can also be hard to fully grasp
because it is so different from
everyday life. Readers may have
previously heard an analogy that
space-time expansion is akin to
galaxies racing away from each
other like fast cars driving in
opposite directions. The reality
is more fantastical than that.
Imagine a not-yet inflated
balloon covered in little dots.
As you blow up the balloon
(hopefully not with precious
helium), the distance betweenthe dots grows. This is what the
expansion of space-time is like.
Galaxies aren’t racing apart but
rather space-time is growing
between them.
This expansion isn’t anything
to worry about, because it is only
happening on very large scales,
not on the scale of our solar
system, where gravity is playing
its part to keep things together.
When our space-time was less
than a second old, this expansion
accelerated faster than the speed
of light for a very brief moment.
Imagine a percentage of a second
with 40 zeros after the decimal.
That is how long cosmic inflation
occurred for. This expansion
was exponential.
To get a sense of what this
means, buy a loaf of bread and
wait until it shows signs of mould.
Once there is a little, it will become
a lot very quickly. This is because
the microorganisms ruiningyour bread are reproducing
at an exponential rate.
One of the challenges that
inflation theory faces is that while
it fits all of our cosmological data
almost perfectly, we haven’t been
able to work out the details. We
still don’t have an exact equation
to describe the energy that
governs inflation.
What we have learned,
however, is that many reasonable
candidates for this energy
equation implicate space-time in
a fantastic trick: it may be eternal.
New bubbles of space-time may
pop up and grow continuously,
with no beginning and no end.
Not everyone loves this idea.
In fact, one of the early architects
of inflation, Paul Steinhardt, has
since become one of the fiercest
critics of inflation – and especially
eternal inflation – and a source
of many editorials challenging its
status in mainstream cosmology.
But so far, no one has offered an
alternative idea for why the
contents of space-time look the
way they do that matches the data
as gracefully as inflation does.
In the meantime, the search
for the right energy equation
continues and there are those
of us who are thinking beyond
inflation to the energy that is
left over after the process is done.
In a series of papers, I and my
colleagues have begun to unravel
how the energy from inflation can
plant the seeds of all the matter
we see in space-time: galaxies,
planets and us. I struggle with the
idea that inflation could be eternal
and the whole of space-time may
not have had a beginning.
That aspect of inflation theory
may not be testable, which makes
many people ask whether it is
still science. I think it is, and I try
to remember that the universe
wasn’t designed to be easy for
me to understand. ❚This column appears
monthly. Up next week:
Graham Lawton“ To understand
cosmic inflation’s
exponential
expansion, watch
how mould spreads
on a loaf of bread”The beginning that has no end Investigations of the universe’s
origins make us repeatedly rediscover that the cosmos is stranger
than we ever imagined, writes Chanda Prescod-WeinsteinField notes from space-time
What I’m reading
I am really enjoying
Hazel Carby’s
Imperial Intimacies:
A tale of two islands.What I’m watching
I’ve been marathon
watching the reboot of
Charmed, and it is great!What I’m working on
What if dark matter
and dark energy were
connected?Chanda’s week
Chanda Prescod-Weinstein
is an assistant professor of
physics and astronomy, and
a core faculty member in
women’s studies at the
University of New Hampshire.
Her research in theoretical
physics focuses on cosmology,
neutron stars and particles
beyond the standard modelViews Columnist