There’s a number that holds some of the deepest secrets in the universe. It’s responsible
for how chemical reactions happen, how stars burn, and is so key to our existence that
if it were off by just a few percentage points — you, me, all of this, might not even be here.
And somehow, it comes out to 1/137. It’s a number that’s baffled scientists
for nearly a century, and according to physicist Richard Feynman,
is “one of the biggest damn mysteries in physics.”
1/137, otherwise known as the fine structure constant, or alpha,
is a fundamental constant of nature.
These numbers are the laws of the cosmos, governing everything
from the force of gravity to the behavior of quantum particles. And to understand
how we get alpha, we need an expert who’s been studying it for decades.
My name Is John Webb, I'm a professor of astrophysics at the University of New South Wales in Sydney,
and we're gonna be talking about varying constants of nature.
The fine-structure constant is formed from a ratio
involving the electron charge, the speed of light, and Planck's constant.
That is the quantity that physicists use to describe how
strong the electromagnetic force is. The electromagnetic force is one of the known
four forces of nature. Very important, the force involved in keeping the structure of
atoms the way that they are.
Because alpha dictates the strength of the electromagnetic force,
it's not tied to the units we typically use to measure things like weight or distance.
It comes straight from nature itself, and that’s why alpha is dimensionless. A dimensionless
constant has no units associated with it, no meters, no seconds, nothing like that.
It's a pure number.
Alpha is a mystery, because its value, 1/137 comes to us with no explanation
as why it has that value. It’s a numerical coincidence, with huge implications for us.
If you change alpha, you change the way that atoms are held together. If it had been a
few percent different in the early universe, hydrogen, for example, might not have been
the most abundant element, but helium might have been. Stars would have evolved very differently,
the evolution of the chemical elements would have been very different to what it was, and
indeed human beings, rocky planets, might not even exist. For a small change in alpha.
And this notion of whether the constants of nature are as constant as we think, has
kept many physicists up late at night. The first mention of it in the scientific literature
was in 1874 by Lord Kelvin, and a friend of his Peter Tait. There were speculations
by Eddington and Hermann Weyl.
Paul Dirac wrote a paper speculating and physicist Wolfgang Pauli
famously quipped, “When I die, my first question to the Devil will be:
What is the meaning of the fine structure constant?”
Ironically, he passed away in Room 137 in a hospital in Zurich.
And to this day, no one’s figured it out.
I first started getting interested in alpha in the 1990s actually.
At that time the Keck telescope was collecting some amazingly good data.
By using observations from Keck and the VLT telescope in Chile, Webb and his team
published papers that found variations in alpha, depending on where you are in the universe,
and that’s been the subject of a spirited debate.
We've been working on this for quite a while, searching
to check whether there's any time or space variability of the fine-structure constant,
and so we do that by looking at quasars all over the sky. They're very bright
and they're quite small, actually.
They emit a huge amount of light from a very small volume of space.
It is thought that they are essentially the centers of galaxies, black holes powered
by accretion from material nearby.
Whilst they're fascinating objects as far as we're concerned, really,
they're just beacons of light shining along a huge path length through
the universe. Whilst that light is on the way, between the quasar and us, inevitably
it gets absorbed by things that intersect the sight line.
When light passes through the halo of an early galaxy,
it's as if it takes a snapshot of physics at that time.
Gaseous halos of early galaxies cause absorption dips in the spectrum of the quasar.
We see all sorts of elements in these absorption dips: iron, magnesium,
nickel, chromium, zinc, aluminum.
They use instruments called spectrographs to analyze the light coming from the quasars to our telescopes.
You can split the light up from the quasar
into its spectrum, and look at all of the different wavelengths that fall
onto your detector.
We know what the elements are. We know how much gas is present.
You can measure it very accurately and we can measure the physical conditions in the gas
clouds that are giving rise to this absorption. So you can think of it like a barcode on a
supermarket product, you see the black lines, and if you change alpha, they all change their
positions. If the fine structure constant were different at that time, then the amount
of energy required to get an electron to change its orbit from one level to another, would
be slightly different. We have a tentative signal that there is some kind of something
strange going on, a spatial variation. Because when we look in one direction in the universe,
we see alpha a little bit smaller.
And if you're looking in the opposite direction, it tends to be a little bit bigger.
Of course, that's been met with several criticisms, quite correctly. That's exactly how a science should proceed.
This is not a confirmed result. It was statistically kind of fairly significant, but the trouble
is the data are very complicated. The instruments are very complicated.
The calibration is very complicated.
As Carl Sagan once said, extraordinary claims require extraordinary evidence —especially
when you're challenging the law of the cosmos.
So the European Southern Observatory
is going to put a brand new instrument called ESPRESSO to the test.
It’s a souped up spectrograph handled by lead project scientist, Paolo Molaro,
to hopefully nail this mystery.
Espresso is a spectrograph that is under vacuum and determines stabilities at the level of one milliKelvin.
The first thing that we had to make
is a cadre tray of optical elements to bring the light from the telescopes
to the lab. And this tray is composed of prisms, lenses, mirrors,
which exactly break the light from the telescope to the lab. When the light of the source is injected
in fibers and the fibers feed the spectrograph, which is contained in a vessel under vacuum
and there are different enclosures that make it terminally stable.
This is the different ball game now.
We will get very, very accurate data.
We had the first run and we are now in the middle of that processing.
We have to verify everything. So the first results will be about in one year.
And if ESPRESSO finds that the fine structure constant varies, it would be a very big deal.
It'd open the door to theories that predict multiple dimensions in space time and potentially,
a grand unified theory of physics.
But whether this number signifies some larger metaphysical
truth remains to be seen. There are kind of two schools of thought. One is that actually,
yes, we will one day when our knowledge advances, be able to explain why the fundamental constants,
including the dimensionless ones, have the values that they do. That's my belief too.
I think we will, one day. But there are other alternative ways of looking at this. It is
interesting that the constants that we do have seem to be finely tuned for our existence.
It leads to this idea of the anthropic principle, and the anthropic principle says basically
this, we shouldn't be surprised to see that the constants of nature are finely tuned for
our existence, because if they were not we would not be here, sitting around talking
about it. And maybe that's from this point of view, all you need.
In fact, they're finely tuned by the hand of God, that's one point of view that
many people probably do hold. There's another point of view, and that is, well, actually
there's an infinite number of universes, and each one of those universes has a different
set of physical laws and we just happen to be in one that we're able to, um, talk about.
I think Stephen Hawking liked that idea.
So there's multiple ideas, there's a lot of thoughts, and
we're probably still at the early days of our understanding.