Physics is full of constants. These are values or properties for which there is no theoretical
basis. They are only determined by measuring them. Some of these constants are things like
the charge of the electron, the gravitational constant, Planck’s constant, and many others.
If any of these numbers were different, our universe, as we know it, would not be the
same. And we probably would not be here if that was the case. Why do these numbers have
the values that they do? For that matter, why are we here? This is
the core of fine tuning argument. It goes something like this:
The constants of nature are statistically improbable. These constants are on a razor’s
edge such that even a slight deviation would likely result in no life as we know it in
the universe. Some take the argument further and say that
this fine tuning is so unlikely, that it could not have occurred by pure chance, that there
must be some agent that set up the constants to enable life.
There are others that reject this argument for various reasons. But the discussion of
finetuning is a very important existential question.
In this video, I will take a look at both sides of the picture, and give you what I
think are compelling arguments both, for and against, the fine tuning of the universe,
so that you can be well informed enough to make your own judgement. And that’s coming
up right now.
Before we look at both sides of the fine tuning argument, I'd like to take a brief moment to
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In considering the case for fine tuning, we can start simply by looking at the constants
associated with the different forces. The most significant force on a cosmological
scale is gravity. The magnitude of the force that one massive object has on another is
determined by the gravitational constant. If this constant was too small, gravity would
be too weak, and planets wouldn’t form because small objects may not be able to conglomerate
to form bigger objects so easily. But if it was too big, the stars would burn
up too fast, and there would not be enough time to form complex life.
This is because, stars and planets form as the gravitational force pull its constituent
particles together to form a celestial body. Stars exist in an equilibrium between the
gravitational force which tries to collapse the star, and the pressure from the energy
of fusion in the core which tends to counteract this force, preventing the star from collapsing.
If gravity were stronger the star would have to burn more fuel to increase the counteracting
pressure to avoid collapsing the star. This means the star would run out of fuel
more quickly, and so the life of the star would be greatly shortened.
The problem is that astrobiology experts say that it takes at least a billion years for
life to form on a planet. But if the stars powering any solar system can’t survive
for that long, then its orbiting planets likely could not contain life. It’s therefore very
important to have the right strength of gravity. Just a 5% increase in the gravitational constant
would result in at least a 1.2 billion year decrease in the lifespan of the sun.
More importantly, earth would orbit around 9-10% closer to the sun. This would lead to
huge climate changes, and this in turn could mean the end of the human species.
If we now consider the electromagnetic constant,
the situation is similar. This electromagnetic force is responsible for the distance at which
electrons orbit in atoms. It determines the size of the atom. If the force was weaker,
the atomic size would increase because electrons would be further away from the nucleus.
This could have an impact on chemistry, as it would change the strength of chemical bonds.
Since the electromagnetic force influences the atomic size, varying the constant of this
force would also change the temperature of the stars. A higher constant would lead to
cooler stars, and a lower constant would lead to hotter stars that would not last long,
just like in the case of gravity. The reason for this is that if the constant
is lower, then the coulomb barrier would be smaller, making it much easier for fusion
to occur. This would make stars burn faster. If on the other hand, the constant is sufficiently
bigger, atoms larger than hydrogen atoms could not form and stars may never ignite, because
protons may not have been able to overcome the coulomb barrier to fuse in the first place.
Also related to the stability of atoms is the strong coupling constant. This is the
constant related to the strength of the strong force which keeps neutrons and protons glued
together in the nuclei of atoms. If it were lower, then again you wouldn’t
have stable heavy atoms as it would not be enough to overcome proton-proton repulsion,
similar to the situation with making the electromagnetic force larger.
If the strong nuclear force was only 1% weaker for example, atoms crucial for life such as
Oxygen, carbon and nitrogen may not form in sufficient quantities inside stars, because
the strong force would be too weak to keep protons and neutrons bound together in the
nucleus. If, on the other hand, the strong force was
2% stronger NO atoms might form, and we could be stuck with only hydrogen atoms. The reason
for this is that the strong force would overpower the beta decay that is necessary for protons
to be transmuted to neutrons. Neutrons are crucial to make the nucleus stable for larger
atoms to form. If neutrons can’t be formed, then all the
heavier atoms beyond hydrogen and helium, that we need for life may not form.
Finally, if the value of the weak force constant was sufficiently bigger, then hydrogen would
have turned into helium during the big bang in such large volumes that stars would either
not exist, or be much more rare. This is because helium forms from the fusion
of 4 hydrogen nuclei. But 2 of these nuclei
have to transmute into neutrons to form helium. This is enabled through a process called beta
decay, which is due to the weak force. If this force was stronger, than it would enable
this fusion process to occur in more abundance, creating less hydrogen and more helium in
the universe. This would not only mean less hydrogen for
stars to use as fuel, but also less hydrogen to make H2O. This means little to no water,
and this means little to no chance for life as we know it to occur in the universe.
If on the other hand, the value was smaller, neutrons wouldn’t have changed into protons
in significant numbers. This would leave us with a universe awash with neutrons, and very
few atoms in the universe. Free floating neutrons would be stable unlike the way they are in the
current universe. But there are many other constants and parameters
which represent other fundamental properties of the universe. And if you similarly changed
those, they could also have some significant effects on how our universe looks.
So as you can see, the idea of fine tuning does appear to be a compelling argument.
Some say that these constants being so finely tuned in order to have the relatively stable,
life producing universe that we have, could not have happened by chance.
But is there another side to this coin? Just
like everything else in life, there are always two sides to every story. So what are the
counterarguments? In general, while the universe appears to
have constants that need to be within a very precise range, such that even slight variations
could result in a different universe, it does not follow that this is unnatural.
There would be no basis to make that judgement because unnatural would mean that other constants
could or should exist naturally. That is not the case.
There is no alternative existence of nature that we can conceive of, in which nature would
have different constants. And we have never measured any alternatives to these constants.
We can’t even say that it’s improbable because probability indicates how likely an
event is to occur. But this presumes that more than one event could occur. When it comes
to this universe, and the constants that it has, this may not be a valid presumption.
We would need to assume that other universes with other constants were possible. We don’t
know whether that is the case. And if it was the case that other universes
with other constants could occur, then there could have been or could be an infinitely
many universes with all combinations of constants. In that scenario, it would be inevitable that
a universe with our constants would be among them.
Statistics can’t be done with one sample. There are lots of things that could be statistically
improbable or impossible, such as the chance of flipping a coin and getting heads 50 times
in a row. This is about one in one quadrillion. I can calculate the probability of that, because
getting a heads or tails are both possible, and I know the probability of each.
No probability based on statistics can be calculated for the different constants of
nature.
But these are philosophical arguments. Are there any scientific ones?
One example which shows that precise fine
tuning may not be the case is in the masses of the different fundamental particles. They
are all measured. But their masses may not be independent. And some studies find that
they must have certain values with respect to each other.
Problems could arise, for example, with the stability of atoms if you changed the quarks’
masses. The same can be said for the electron. Although it is important that the down quark
has a higher mass than the up quark to enable beta decay, which allows neutrons to transmute
into protons and vise versa, the precise value of these quark masses appears somewhat arbitrary.
They could have different values, but as long as the difference between them was about the
same, not much seems to change. For example the mass of the proton overall
would not change much since the quark masses only constitute about 1% of the total mass
of the proton. The same applies to the neutron. It will have an effect in particle physics
experiments such as that at the LHC, but in terms of macro level effects on life, it may
not make any difference. Another case against fine tuning appears to
be the mass of the neutrino. In the classic standard model it was predicted to be massless,
but we know now that it does have a very small mass because of measurements made on solar
neutrinos. However, the exact mass of the neutrino seems to be arbitrary.
The most important thing is just for the mass to be very close to zero, and the ratio of
the masses of the three different neutrinos – electron, muon and tau neutrinos is important.
But the precise number that the mass takes does not seem to make a difference.
So the mass of the neutrino appears to be somewhat arbitrary, which is really the opposite
of finetuning. The same thing applies some other masses, such as the mass of the Higgs
Boson – which also appears to be somewhat arbitrary.
Some finetuning arguments focus on the necessity of carbon. But carbon just happens to be very
abundant, and it is a very versatile element because it can form bonds with other elements
to make complex molecules. But biochemists suggest that life can be based
on elements other than carbon too, such as silicon and Germanium. It would be very different,
but not impossible. Our anthropic bias may be constraining our imagination.
I am reminded of the story of the sentient puddle. This was told by science fiction writer
Douglas Adams. A puddle wakes up one morning after a night of rain and says, this is an interesting hole I find
myself in. Fits me rather well, in fact, it fits me perfectly. It must have been made
to have me in it. And as the sun rises, and the water evaporates, the puddle keeps thinking
that the hole was made to have him in it, until he disappears. But there could be lots
of holes with lots of sentient puddles with different dimensions of the hole.
Similarly, if we change the constants, analogous to the dimensions of the hole, it would be
an alternate universe. But life as we know it then, may be different. And would we continue
to say in that alternate existence, this universe must have been made to have us in it.
What is the definition of life. Could life a be Boltzmann brain, for example, a sentient
information processor existing in space, or any is it any entity that uses energy, responds
to change, and replicates itself? There could be many ways that life could exist,
but our brains may be confined to think of life like ours being the only kind of life.
And this universe made uniquely for that kind of life in it.
If the universe was fine tuned for life, why doesn’t life play a central role in the
universe? Why isn’t it everywhere? Why is most of the universe hostile towards
life. We could not exist for example, in space or on any other planet without lifesaving
technologies. Even if the universe is finetuned, it does
not necessarily mean that there is an agent that created it. If an agent, such as a God
created life, presumably this agent would be outside the bounds of physics that he created
in this universe.If that is the case, why must there be finetuning in the first place?
This agent can do whatever the heck he wants. If he wants there to be life, he can create
life in a totally chaotic universe. Why is he bound by finetuning?
He could create life in a universe that had a lot of slop, where the constants could vary
a lot. He could create life if the mass of the electron was as much as a house. The
agent is not bounded by any laws of physics, because he would have created those laws to
begin with. So it may not follow that an agent exists even if there is fine tuning.
The precise reasons why the masses are what they are, and the constants are what they
are is an open question though. We can only speculate at this point. But one of the main things
we should keep in mind is that our understanding of the universe, is incomplete. And we know
it is incomplete. We can’t explain dark matter, dark energy, the asymmetry of matter
vs antimatter, and a host of other things. It is quite possible that a future more complete
theory that may extend the standard model and perhaps incorporate a quantum theory of
gravity, could not only answer these questions, but also explain the theoretical bases for
the constants being what they are. We saw a similar breakthrough with the electroweak
theory, which united the weak force with electromagnetism. It showed that when we go to higher energies,
two seemingly unrelated forces – electromagnetism and the weak nuclear force,
unite, giving us a deeper understanding of the universe.
There is a lot more physics for us to learn. And the future is probably going to be full of
aha moments. Einstein said that “Nature shows us only the tail of the lion…but there
is no doubt the lion belongs with it…we see the lion only as a louse sitting upon
him would.” It is possible we simply have not yet seen
the lion that awaits at the end of the tail. And if you have a question, post it in the
comments because I try to answer all of them. And if you like videos like this, then hit
the subscribe button. It costs you nothing. I will see you in the next video my friend.