The holy grail of physics is a theory of everything. It would describe the true
nature of reality. It would give us the answer to the questions like, "what is
dark energy?" And, "what is dark matter?" It would unite quantum mechanics with
general relativity, and help us understand the behavior of gravity at
the smallest scales. Such a theory would likely show the origin of all forces
emanating from perhaps one master force, and the origin of all particles
emanating from perhaps one super particle. It would be the ultimate answer
to every question that asks why something is the way that it is. Do we
have such a theory? No, but we have something that comes close to it. And it
may give us a clue as to the true nature of reality. Let's look at what this is
and figure out what it may be trying to tell us about the true nature of
existence. That's coming up right now...
We don't have a theory of everything, but we have something that comes a
significant fraction of the way to being there. This is called the standard
model of particle physics. This is the most successful and tested model
describing the true nature of reality that we have ever had. This model is so
good in fact, that when the theory of everything is discovered, it will have to
be a refinement of the standard model - just like Einstein's theory of General
Relativity is a refinement of Newton's law of universal gravitation. This model
explains the subatomic makeup of all atoms, explains chemistry, magnetism
nuclear physics, and many other things. The only thing it's missing is gravity.
Gravity doesn't work using the equations of quantum mechanics. And there's no
quantum theory of gravity yet. But the standard model does not predict
absolutely everything. It shows us the fundamental particles that make up all
matter, and three of the four forces governing them. But there are 19
parameters that it does not predict. These parameters have to be calculated
through measurement and put in as constants within the model.
What are these 19 parameters? These are masses of the six quarks and three of
the leptons, mass of the Higgs boson and strength of the Higgs field, how four
of the quarks decay, strength of the electromagnetic field, strong, and weak
forces, and the number describing the strong force interaction between quarks
and gluons. These are called free parameters. And there 19 of them. So these
are all constants that have to be measured, and put into the equations.
There's nothing that predicts these. If you were to ask, "why are these constants
equal to the number that they are?" I would just have to tell you that it's
just the way that our universe happens to be. From what we can tell, in a
different universe, these parameters could have been different. Now, there may
be an underlying theory that shows us that these numbers could not be anything
other than what we observe, but that doesn't seem to be the case from what we
understand about physics so far. What would happen if these constants or some
other number, rather than the number that we observe? Well, depending on the number
you're talking about, and the magnitude of the change in that number, our
universe would be anywhere from being slightly different, to being completely
different. So for example, if the strength of the electromagnetic force was
stronger, we would likely have smaller atoms. But chemistry would probably still
exist. The universe may only be slightly different in that case. However, if the
masses of the up and down quarks was much different, there would be no atoms
and we would have a completely different universe. why? Because it would change the
relative mass of protons and neutrons. Neutrons in our universe are only about
0.1% more massive than protons. But this difference is crucial because it allows
neutrons to decay into protons, and an electron, and an anti-neutrino. If the
relative mass was reversed, then protons would decay instead into neutrons. And
eventually, we would end up with the universe full of neutrons. No protons
means no atoms. And no solid structures. And no chemistry. This is the crux of the
fine-tuning argument - that these constants along with other constants in
the universe such as the gravitational constant of general relativity, and the
cosmological constant, appear to be such that life in our particular
universe can exist. I'll get into the details of the fine-tuning argument in
another video, but for now, let's take a look at what would happen if these
constants were different. Potentially, you could have a set of universes that was
something like this number. the "R" represents the variations of the numbers
that would make a different universe. This could be a very large number,
depending on the magnitude of the change that could cause a completely different
universe, because some of these numbers only have to be different by one in a
thousand parts or more. So for example a thousand to the nineteenth power is a
huge number. Added together, these numbers may indicate a truly mind-bogglingly
large number of different universes. if these constants turn out to be indeed
arbitrary, not based on any underlying theory, then it may lend credence to the
multiverse theory of reality. In other words, there could be universes where
every variation of these numbers has happened. In fact, a version of the most
studied theory of everything and the one that has the greatest number of
physicists working on it, predicts such a vast number of multiple universes.
This is m-theory, or membrane theory, which is a theory that unites all the
consistent versions of string theory. M-theory brought all the string theories together
by asserting that strings are really one-dimensional slices of a
two-dimensional membrane, vibrating in 11-dimensional space-time. This is a
candidate for a theory of everything, that many physicists support. And if true,
it could represent the true nature of reality. Some estimates have shown that
the number of multiverse predicted by this theory is 10 to the 500 power.
That's 1 followed by 500 zeroes. This is unimaginably huge. Now this theory has
some problems though. Like it predicts the existence of a subatomic particle
called a graviton which has not been detected so far. It also requires the
universe to have up to 11 dimensions, because the strings have to be able to
vibrate in these number of dimensions in order for the theory to work
mathematically. 11-dimensional mathematics is also so complex that the
theory has been derided by many including me because its mathematics
can be manipulated to represent almost any imaginable universe. But what if it's
true? Maybe almost any imaginable universe actually exists. Maybe, given the
number of physicists that support it and are working on it,
could it be that they're in fact on the right track? Could they be onto something?
But if this is really true, then where are the other dimensions? We only see
three spatial dimensions, and one time dimension. Where are the other six to seven
dimensions required by this theory? String theorists say that these
dimensions may be compactify on a very small scale. So for example, a rug looks
two-dimensional from very far away, but close up, you can see that it has a third
dimension of thickness. And it also has small loops and textures on its surface
similar to representing other potential dimensions. For example, if you go down to
the scales that are closer to the scale of a Planck length, extra dimensions may
be loops as shown on the grid here. Now imagine the loops being more complex
shapes, like a Calabi-Yau manifold. This is a mathematical shape that can
containt all of the six missing dimensions. Now imagine a string vibrating not only
in our three dimensions, but since strings can be really small, they can
vibrate in these smaller dimensions as well. The way they vibrate determines the
particles that they represent. One vibration can be a photon. Another
vibration can be gravity. Another can be an electron, or other form of matter. In
string theory, the strings and their vibrations are affected by the geometry
in which those strings are moving. The issue is that the shape of those extra
dimensions is not known. But if it was known, then the mathematics of string
theory could tell you exactly what the vibrations would be. And this would give
us a theoretical basis for why the parameters are the numbers that they are.
In other words, the shape of the extra dimensions may determine the exact
magnitude of those parameters. And if these shapes were any different, then the
numbers would be different. And the universe as we know it would not exist.
A different universe would exist perhaps. Does this mean that the numbers
could have been different if the shape of the dimensions was different? That is
possible. Is there any way to test for these extra dimensions? It turns out
there is - using the Large Hadron Collider. If after a collision of particles at
extremely high energy, scientists detect less energy than was present in the two
particles before the collision, then this would be an indication that the missing
energy may have been transferred to these extra dimensions. So what has the
LHC found? Well so far, the LHC has not found extra dimensions. But even if we
found out the shape of the extra dimensions, and determined that the math
of string theory predicts the exact numbers that we measured, this may still
leave the question of why the shape of those extra dimensions is the way that
it is. So even if string theory answers the question of the true nature of the
universe, it may still imply that there could be other universes where the
shapes of those extra dimensions are different than what we observe. So why
does our universe happen to be the way that it is? Why do we find ourselves in
this relatively peaceful, orderly universe
that supports life? Why should nature favor one kind of
universe, or one type of existence over another? There doesn't seem to be any
reason for that. You could invoke God here, and say that it was a supernatural
force that caused this through his or her sheer will, or divine intervention. An
intriguing alternative and possibly testable theory, is that we are part of a
large multiverse, perhaps one of a multitude of membranes of the m-theory.
How could we test for this? The LHC could give us a clue. The soon-to-be-launched
James Webb telescope will allow us to peer farther in space, and further back
in time, and perhaps find an anomaly that indicates the influence with another
membrane. In the future, we may even be able to simulate multiple dimensions and
universes. It may be that we just happen to find ourselves in that one universe,
out of innumerable other ones, were the shapes of our compacted dimensions
happen to be such that life is possible. There's no other membrane where we would
find ourselves. This universe perhaps is nothing special. It is but one of many
possible universes that may number something like 10 to the 500 or more. And
the only thing that may make this universe unique, is that you are in it.
And I my friend, am glad that you are!