What if we held a giant mirror up to our
universe and then built that reflection?
Everything is pretty much the same just
flipped. Are the laws of physics, gravity,
Newton's forces, magnetism, still working
the same way they do in ours? If we
checked back in a trillion trillion years
would they still be perfect reflections?
This seems like a simple question. Yes
right? If everything is exactly the same
just flipped, why wouldn't everything
behave the exact same way just flipped?
Well what does flipping or mirroring
something actually do? If you've ever
looked into a mirror
you'll probably notice just one
difference. Everything that's on your
left is now on your right and everything
that's on your right is now on your left.
This is all reflection really is
swapping left and right. But does this
have any kind of impact on the laws of
physics?
Would physics even you notice if left
and right were swapped? For example if
things all of a sudden started falling
up physics would be like "hello" what
happened to gravity? This is against the
rules. But if left and right were switched
is this breaking any rules? This is kind
of a hard concept to grasp and not one
we would usually ask ourselves, so I'm
going to borrow an analogy from the
great physicist and Bongo player Richard
Feynman. He says imagine you're talking
to an alien in a faraway galaxy. Let's
call him Simon. Simon is old-school and
he's not big on smartphones, so sending
pictures is out of the question. All you
really have in common are the physical
laws of the universe, so if you can
explain to him what left and right are
using only physics then there must be
some kind of rule that says left has to
be left and right has to be right. So can
you do it? Maybe you'd warm up with
geography. If you're standing in
Melbourne looking at Adelaide, Sydney is
on your right, so we can define left and
right on earth, but try telling this to
Simon he'd have no idea what you were
talking about. There's nothing in the
laws of physics to say that Sydney
couldn't be to the left of Melbourne.
Defining left and right by geography is
just convention in
vented by us humans and doesn't mean
much to Simon. Okay that was just a
warm-up. A better example that seems to
distinguish between left and right is
life. Amino acids are the building blocks
of life and one that shows up a lot is
called alanine. Amino acids usually have
a left and right-handed version but when
we find alanine in nature it's always
left-handed. What's even stranger is that
when we make it synthetically in a lab
equal amounts of left and right-handed
molecules are created, yet life is all
left-handed. So if we bubble up a
synthetic right-handed fly and fed it to
a frog, it wouldn't be able to digest it
because all of its digestive enzymes are
the wrong way around. They're made for a
left-handed fly. So it would seem as
though life does make some kind of
distinction between left and right. So
you say "hey Simon, take a look at the
alanine molecules in life on your planet,
whichever way they're facing that's
left-handed'. But wait, is there a reason
life on his planet couldn't be
right-handed? Our synthetic right-handed
fly didn't work but that's just because
of the way it reacted with a left-handed
frog. If Simon's planet had
right-handed flies and right-handed
frogs, that would work out fine. But
didn't we just say all life was
left-handed?
Well yes, life on earth. 3.8 billion years
ago when life was first forming on earth
some left-handed molecules just happened
to win over some right-handed ones and
from then on life gradually became
left-handed. It could have easily gone
the other way and physics had no say in
the matter. It was just pure chance. So if
we told Simon that life on his planet is
left-handed there's a 50% chance we'd be
wrong. There's just as good a chance that
life on Planet Simon is right-handed as
there is left. But now we come to
something which sounds pretty promising.
Left and right in physics.
Physics has many left and right hand
rules, for example if you take a magnet
and wrap a wire around it
the magnetic field will produce a
current through
the wire. If the north pole is pointing
up the current flows to the right, if the
South Pole points up the current flows
to the left.
Magnets are the same everywhere in the
universe, electrons are the same
everywhere in the universe, so the
current should flow to the same way
everywhere in the universe. You tell
Simon "find a magnet and wrap some wire
around it,
make sure the South Pole is pointing up
and then the direction the current flows
is left and the opposite of that is
right", to which he'll say: "which is the
South Pole?". You could say the difference
between the North and South Pole is that
the North Pole points north and the
south pole points south, which seems fair,
but the thing is, that doesn't mean
anything outside of Earth. The north and
south pole of a planet depend on its
spin. The Earth spins counterclockwise
but if it spun the other way the
north and South Pole would be reversed. So
let's just ask Simon which way his
planet is spinning, easy right? Then we
could tell him what north and south are
and he could figure out left and right
from the magnet and wire. Unfortunately
that kind of leads us back to where we
started.
If you look closely enough into any
right or left-hand rule in physics it
always breaks down at some point. What
would be a physical difference is if
the South Pole were growing tiny hairs
for example. Then we could tell Simon the
South Pole is the one with the tiny
hairs and he'd know instantly what we
were talking about. But so far we are no
closer to telling him what left and
right are and he's getting pretty
impatient. But we've still got one more trick
up our sleeve. In the 50s an experiment
was performed at the University of
Columbia using a very strong magnet at a
very low temperature. At extremely low
temperatures it turns out a certain
isotope of cobalt becomes magnetic.
These tiny cobalt magnets will line up
in the magnetic field and when they
disintegrate they emit an electron and
it was discovered that the majority of
electrons will always fly away from the
South Pole. This may not sound like much
but we've just discovered a physical way
to distinguish the South Pole from the
North. When a
magnetized cobalt atom disintegrates the
majority of electrons will fly in the
direction away from the South Pole.
Basically the magnet has grown hairs! And
if there's a physical difference between
the North and South that means there's a
physical difference between left and
right. Put it this way: we can now tell
Simon "cool your magnet and wire system
down to nearly zero degrees Kelvin, then
get some cobalt atoms and line them up
in the magnetic field. Now arrange
everything so that when the cobalt
disintegrates the electrons fly up
towards the sky, then the direction the
current flows is to the left and the
opposite of that is right", to which he'll
say "Thank You human, I understand". This
type of reaction is called
weak decay and it's very rare, but even
so it means physics would notice if left
and right were switched. Remember how we
said the Earth's North and South Pole
depend on the direction it's spinning?
This is the same for magnets, the North
and South Pole depend on the direction
the electrons within it are spinning. So if
in our universe they were spinning to
the right the electrons in the mirror
universe would be spinning to the left,
which means that the North and South
Poles would be opposite. So when our
cobalt atoms disintegrate the electrons
in our universe would go up whereas the
electrons in the mirror universe would
go down, breaking the reflection. This may
not sound like enough to throw our
mirror universes off but when we're
talking trillions and trillions of years
any tiny difference becomes massive. I
don't know what we'd see when we looked
back but I do know it wouldn't be this...
Thanks for watching guys I hope you
enjoyed this! Make sure to leave a like
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