The Double Slit Experiments
Now just for those that aren’t familiar with the double slit experiment. We did this in my high
school physics class and maybe you did it in high school too. But the background for this is the
single slit experiment. If a beam of light is shined on a narrow slit, just one simple band of light
forms on the dark screen on the other side of the slit. Now if two parallel slits are used there
is an interference pattern of many alternating bands of light and dark that is formed. The idea
is that the waves of light from one slit interferes with the waves of light from the other slit. So
where both waves hit and the peaks of both waves are in sync there is a band of light. Where
they both hit and one wave is at its peak the other wave is at a low, they cancel each other out
and there is a dark band. I think the light may also need to be in-phase parallel light of just
one frequency for the clearest results.
OK, now this makes sense so far. But photons are usually considered particles not waves. So
instead of shining a light on the slits, scientists can fire a single photon at the two slits and fire
them at say 10 second intervals. But guess what – they get the same interference pattern
formed after a period of time.
How do the photons interfere with each other when they are fired one at a time? So is light a
wave or a particle? Now for some of the answers I have heard over the years. I don’t think
any of them hit the nail on the head.
1. When particles move they move as a wave. This seemed to make sense but did not
really explain what was happening.
2. The photon goes through both slits at the same time and therefore interferes with itself.
3. The photon takes every available path to the other side including going to the
Andromeda galaxy first and coming back. So it can end up anywhere on the other side
of the slits, but most only in one of the bands of light. I think it was Feynman that came
up with this originally.
4. The photon behaves according to a wave probability function that gives more
probability to the light bands and less probability to the dark bands and hits as a particle
at that spot according to the distribution this wave function gives it.
5. One author said the wave function is like a storm cloud with a photon bouncing all
around inside the large cloud. When the cloud hits the screen the photon hits at the
location it was in at that point. This makes some sense.
6. Victor Sanger gave this explanation, which I like: There are no waves, everything is a
particle. The interference pattern only appears when photons en masse are involved.
This discussion also involves the Heisenberg Uncertainty principle. This states you cannot
simultaneously determine both the mass/energy and the location of a particle. This seems to
be exactly what we are trying to do. If it is a wave where is the particle? If it is a particle how
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can it interfere with itself? Stenger also says scientists can confuse their math with the reality
of the subject. I think I have seen this in several authors. What happens if light is a wave, is
different than if it is a particle. The dark bands are where waves cancel each other out, or they
are where the photons can’t go. Wave theory says the waves are additive. Particle theory
says they can’t be in the same place at the same time.
My take on this is that the probability wave function gives a mathematical function that
describes what we observe, but that is not what is actually happening. The fact that light
appears to be a wave and a particle says to me that maybe it is neither one. What intrigues
me about string theory is it seems to have possibilities of answers for this and for other
problems where our math fails us.
String Theory
A string is something that can vibrate and can have a quark on each end with each quark
moving at the speed of light. Plus it exists in 11 dimensions and can vibrate in at least 10 of
them. Now it would seem this object would have a behavior that could be like a wave and a
particle at the same time. 11 dimensions could explain a very complex interaction
(interference?) between itself and itself. And why would an 11 dimensional universe be
limited to just 1 dimensional objects – strings. Why not 2 or 3 or 6 dimensional objects?
Those are called branes. I think String Theory has all the complexity a physicist trying to come
up with the theory of everything can stand. Maybe it hurts Lee’s brain too.
Now string theory has several brick walls that theorists are trying to break down before other
theorists and physicists consider it as accepted science, if they ever do. One of course is the
size of the strings that are many orders of magnitude less than subatomic, but there are other
very complex issues. Such as: which of tens of thousands of Calabi-Yau shapes describe how
the 6 rolled up dimensions are rolled up in our universe.
As far as the discussion on determinism goes I think any talk of probabilities seems to be
saying there is element of randomness here, when in fact it is really saying there is a pattern
here of which we have no understanding, but we can create a mathematical function that
mimics the pattern. We can use that function until we have a theory that can actually explain
the pattern we are seeing and make predictions we can check.
Virtual Particles, Quantum Foam
They call them virtual particles, but that doesn’t mean they are imaginary. They have mass
and movement. The reason they are called virtual is because they pop into existence and then
disappear. They occur around an atom and part of the atoms mass is due to the virtual
particles. They are virtual and disappear, but it happens so frequently that there are always
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virtual particles there. It also happens around the particle itself. That is the reason Hawking
said a black hole will eventually evaporate. A photon is just inside the event horizon and a
virtual photon appears just outside the event horizon. The one inside can’t escape gravity, but
the one outside shoots off away from the black hole at the speed of light.
Now these virtual particles also appear in empty space where there are no other particles
around. This has ramifications for cosmology both for understanding our own universe and its
origins and even aspects of a wider multiverse. So the virtual particles or quantum foam may
help explain the double slit experiments and the Heisenberg Uncertainty Principle.
Quantum theory also says two particles cannot occupy the same space. This also is part of the
discussion on locality and mass/energy when we talk about waves or particles. Interestingly,
this limitation means there is a finite limit to the places a particle can be in our finite universe.
That means given the finite number of particles in our universe there is also a finite number of
ways to arrange those particles. This number is very large and has been calculated. Of course
it is growing as our universe expands.
Inflation (an amazing aside)
And it is ridiculous now to talk of the visible universe as being the size of our universe. We had
thought that the galaxies beyond Hubble limit were receding from us faster than the speed of
light and also they haven’t existed long enough for us to see them farther away than 13.8
billion light years. But with inflation we know the universe was expanding orders of
magnitude faster than light. Consider that the most distant galaxy we can see 13.8 billion light
years away is as it was shortly after the big bang. But an observer on that galaxy, now just as
old as ours, would look in our direction and would see us at the edge of his universe. That
observer would not see the 13.8 billion light years of galaxies that we can see in the opposite
direction. Just as we cannot see the 13.8 billion light years that lie beyond his galaxy. With
inflation Guth estimates that our universe may contain 1023 times as many as the 150 billion
galaxies we can see and maybe much more. Now that is a fair sized universe I would say. But
that is just my opinion. Stenger says that the galaxies we see at 13.8 billion light years are
now actually at 46 billion light years away considering the inflation and expansion that took
place in those 13.8 billion years. He says the multiverse is the natural result of eternal
inflation.
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