About a hundred years ago, our understanding
of the fundamental governing rules of the
universe changed in a radical way.
Rather than the simple and relatively intuitive
world of pendulums and pulleys, Newton's law
of gravity and Maxwell's equations of electromagnetism,
the discovery of quantum mechanics and Einstein's
theory of relativity showed us that, at its
core, the universe behaves in rather unexpected
and non-intuitive ways.
We learned that moving and stationary clocks
tick at different rates and that Schroedinger's
cat was simultaneously dead and alive.
These ideas, and others like them, have bothered
scientists both professional and amateur,
for nearly a century.
In fact, it's unusual that a week goes by
when I don't receive an email or letter from
some curious soul who thinks they have found
a fatal flaw in the theories of quantum mechanics
and relativity.
It is very rare that these communications
include an idea that wasn't asked and answered
years ago.
The simple fact is that, while these theories
are counter-intuitive for most people, they
also agree remarkably well with measurements.
Like it or not, they're here to stay.
Special relativity was developed in 1905 and
it was in the 1920s in which a cadre of physicists
worked out the rules of quantum mechanics.
Initially, these two theories were invented
independently, but if they were both true,
then the two ideas needed to be blended together
into a theory that is now called relativistic
quantum mechanics.
In 1928, British physicist Paul Dirac began
that process.
His equations predicted a new form of matter
existed, what we now call antimatter.
I talked about antimatter in another video,
but the upshot is that the discovery of antimatter
in 1932 by Carl Anderson gave physicists considerable
reason to not only believe in quantum mechanics
and relativity separately, but also to believe
that Dirac had combined them properly.
The 1940s brought with them a fuller understanding
of the quantum realm.
Physicists Richard Feynman, Julian Schwinger
and Sin Itiro Tomonaga developed what we now
call Quantum Electrodynamics or QED.
QED is not only a fully relativistic quantum
theory; it also "quantized" the electric field.
In much the same way that early quantum mechanics
showed that matter came in discrete packets,
QED showed that the electric field also came
in packets that we now call photons.
If you feel that quantum mechanics and relativity
have made unsettling claims about reality,
Quantum Mechanics will give you an ulcer.
QED describes two electrons scattering from
one another as one electron emitting a photon,
while the other absorbs it.
That's not so hard to imagine.
However, the exchanged photons differ from
the familiar massless photons of ordinary
light.
For one thing, the photons of QED can actually
have a large mass.
This is not a problem in the quantum world,
which is governed by, among other things,
the Heisenberg Uncertainty Principle.
Boiled down to its essence, this principle
says that extra energy can simply "just appear"
for a brief moment, as long it disappears
quickly.
The bigger amount of energy that appears,
the shorter amount of time it can exist.
Although the idea of massive photons already
sounds pretty crazy, QED isn't done yet.
If you follow that idea a little further,
you find out that QED predicts that nothing
is really something.
I'll wait while you process that last sentence.
Nothing is really something.
So let's see what that means.
We'll start by taking this box, which is filled
with air.
The next step is to take all the air out of
it and shield it so there are no external
energy fields seeping into it.
With nothing inside, surely it's empty.
Right?
Well let's start zooming in.
Maestro, can you zoom a bit?
Nope... not seeing anything.
Maybe a little more?
This isn't getting us anywhere.
Time to pull out the big guns.
Maestro, can you do the quantum zoom?
The image you�re seeing gives you an idea
of the smallest quantum reality.
The flickering colors represent the constant
creation and destruction of matter and antimatter.
Electrons and antimatter electrons, quarks
and antimatter quarks... they are created
from nothing and disappear back into nothingness.
We can see that when we look at what is going
on at the smallest and most quantum of scales
that empty space is actually extremely busy.
Scientists have a name for these effervescent
subatomic objects.
They are called virtual particles.
There are lots of other ways to visualize
this, but one way is to think of the foam
on a particularly fizzy root beer.
If you look closely, you can see bubbles appearing
and disappearing in an ever-changing way.
For this reason, some scientists call these
virtual particles "quantum foam."
Yeah, yeah, I know.
This just sounds entirely impossible.
So, how do we know it is true?
There are lots of reasons, but we can talk
about two that are really totally cool.
The first one is what we call the Casimir
effect, first predicted by Hendrick Casimir.
This effect is pretty easy to understand.
The way it works is the following.
Start by assuming that virtual particles exist
everywhere in space.
Now take two metal plates and put them near
one another.
Let's think about what is going on.
You've heard that in quantum mechanics that
particles have both particle and wave properties
and this is true of virtual particles as well.
These virtual particles have both long wavelengths
and short ones and everything in between.
Furthermore, they occur everywhere.
However, the plates introduce a new factor
to the situation.
Outside the plates, both long and short wavelength
particles can exist.
However, between the plates, long wavelength
particles can't fit.
Thus there are more virtual particles outside
the plates and the imbalance causes the plates
to move together.
So, what do we see?
Well, when we do the experiment, we see exactly
what Casimir predicted.
This is considered very strong evidence for
the existence of virtual particles.
There is another measurement that supports
the virtual particle idea.
This has to do with the strength of the magnet
formed by individual electrons.
Electrons have electric charge and they also
act as if they spin.
Just as in the classical world, a rotating
charged object becomes a magnet.
And, because we know the electron's charge
and spin, we can predict the strength of the
magnet each should electron should be.
When the prediction and measured strength
of the magnet formed by an electron were compared,
there was a tiny discrepancy.
They disagreed by 0.1%- one part in a thousand.
A small effect to be sure, but a disagreement
nonetheless.
However, when the simple calculation was replaced
by one using quantum electrodynamics and virtual
particles, the agreement between data and
theory was restored.
And the restoration was better than anyone
had dreamed.
The two numbers now agree to 12 digits.
This is the most accurate measurement mankind
has ever made.
This incredible level of agreement is believed
to be definitive evidence of the existence
of the quantum foam.
Now, let me whet your appetite for something
interesting.
When we make a similar measurement of the
magnetic strength of the muon, which is a
cousin of the electron, the agreement is still
good - it goes out to 8 places - but a disagreement
appears in the 9th digit.
While this discrepancy could be because of
a faulty calculation or measurement, scientists
are pretty confident that the disagreement
is real.
It could be the first sign that our theories
are breaking down.
Scientists are so intrigued that they have
embarked on a new experimental program to
better measure the magnetic strength of the
muon.
The g-2 experiment studied the muon for many
years at the Brookhaven National Laboratory.
Limitations in the existing accelerator complex
led scientists to move portions of the accelerator
and detector to Fermilab, which has the ability
to make more muons and thereby study this
phenomenon more precisely.
The g-2 experiment is expected to begin operations
in 2016 or so.
We scientists are incredibly interested in
the outcome of this experiment, as it may
lead to a new and better understanding of
the universe.
However, even with this exciting discrepancy,
we must not lose sight of the fact that the
agreement between the predicted and measured
strength of these subatomic magnets is spectacularly
good.
This agreement, combined with the observed
Casimir effect, gives incredible confidence
in the quantum foam.
And the idea of quantum foam leads to an entirely
new paradigm- a completely different way of
thinking about space.
Empty space isn't empty.
It's a bubbling, writhing, frantic place,
with energy converting to matter and back
to energy again.
I understand if the claim sounds hard to believe.
But this new view of the subatomic world is
real and scientists can prove it.
You may never look at foam 
the same way again.
