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A few weeks ago, some very
excitable science journalists
were plastering the
internet with headlines,
like "Fifth Fundamental
Force of Nature Discovered."
What was that all about?
Is there really a new force?
Can I finally get my
X-wing out of that swamp?
Let me make it sound
a little less hyped.
There was something
slightly weird about how
a bunch of beryllium
atoms were acting,
that told physicists that for
a tiny fraction of a second
an unknown particle
may have existed.
Hm.
All right.
Let me make it sound a
little more hyped, but also
a lot more specific.
Atomic nuclei have
energy levels,
just like their
electron shells do.
Protons and neutrons can
occupy excited states,
contain excess energy.
And when they settle
down again, they
give off that energy as
photons, but also sometimes
as a particle or a
particle-antiparticle pair.
One thing that comes out of
a pile of beryllium-8 atoms
is a lot of
electron-positron pairs.
They can pop out at a lot
of different energies.
Researchers noticed a slight
excess in their energies
at 17 megaelectron volts.
It's as though something
with a mass energy
equivalence of 17 MEV was
decaying into those particles.
Now, this might sound
a little bit familiar.
The same sort of excess in the
photons emitted after proton
collisions in the
Large Hadron Collider
led to the discovery
of the Higgs boson.
Just recently a new very
slow excess of the LHC
was originally thought
to be a new particle.
But It was discovered to have
been a statistical fluke.
But this excess in
the beryllium-8 decay
is not slight.
It's now a 6.8 sigma excess,
which is statisticease
for it being pretty darn
certain that something weird is
going on.
But why do they think
that the mysterious 17 MEV
particle is a new type
of fundamental force?
Well, in short, it's
because the anomaly
was observed for a very
particular transition
between the beryllium
nuclear states.
That transition meant
a difference in energy,
but also a difference in
some of the quantum stuff,
spin parity and isospin.
And the easiest
way to explain this
is if a spin-1 gauge
boson was created.
Such a particle would
be a mild extension
of the standard model, not too
crazy, but certainly brand new
physics.
Yes, a new spin-1 gauge boson.
No, seriously, this is
awesome, if it's true.
See, three of the four
fundamental forces,
electromagnetism and the
strong and weak nuclear forces,
are all communicated by
these gauge bosons things.
A new gauge boson means
a new fundamental force.
Why are we only
spotting this thing now?
Well, the standard wisdom
for finding new particles
is to create higher
and higher energies;
hence, the Large
Hadron Collider.
Any particle capable of
existing at lower energies
should have been spotted.
But that's not true if
the particle is a ninja.
By that, I mean dark
to electromagnetism
and generally interacting with
regular matter very little.
If that's the case, it could be
produced at much lower energies
than the gigaelectronvolt
energies produced in the LHC,
like the megaelectronvolt
transitions
of atomic nuclear energy levels.
If the decay product
of such a transition
is very weakly interacting,
these particles
could be everywhere and we
wouldn't know it, like ninjas
and like dark matter.
In fact, this is a
tantalizing possibility.
Not that dark matter is ninjas.
Although, as a
scientist, I'd need
to test that before
I ruled it out.
No.
I mean that this new
particle may have something
to do with dark matter.
It's very weakly interacting.
But the researchers suggest
it could mediate interactions
between the
so-called dark sector
and the visible universe.
OK, on to the solution to
the quantum eraser challenge.
To summarize, I
asked you to tell me
why it's impossible to
send any real data back
in time using the delayed choice
quantum eraser experiment,
and so cheat on the lottery?
Remember, the landing location
of each individual photon
passing through to
the interference
screen of this
experiment does seem
to be influenced
by a decision that
is made regarding each of those
photon's entangled partners
in the future.
That decision was
whether we would
know the path of
the original photon,
thus eliminating any
interference pattern,
or to erase our knowledge
of that path, which brings
the interference pattern back.
That decision is made
randomly by a beam splitter
in the original experiment.
But it's conceivable
that the experiment
could be adjusted so that a
person could make the decision.
So why can't I send winning
lottery numbers back to myself?
The reason is that
there's absolutely
no way to tell if any given
photon at the interference
screen has a known
path until you compare
the results of the screen with
the results at the detector.
In fact, the distribution
of photons at the screen
always looks like a single
blurred distribution.
There's no visible
interference pattern at all.
It's only when you
flag which photons
had twins arriving
at detectors A, B, C,
or D that you see
patterns arise.
In fact, even if you remove
all of the A and B photons,
you still don't see an
interference pattern
until you distinguish
C versus D.
And this is because those
photons have interference bands
that are exactly out of phase.
The peaks of C line up
with the troughs of D.
And together, they look
like the same sort of blur
you get if you combine A and B.
This is pretty insane.
The photon positions are decided
and presumably those patterns
are embedded in
the distribution.
Those embedded patterns are
set by the eventual destination
of the entangled partners
of those photons.
But the distribution
may be in place
long before those twins
finish their journey.
Yet, we can't
extract the patterns
of the photons that
landed at the screen
until we get the information
of which detectors
their entangled twins hit.
That information can't travel
backwards in time or faster
than light.
So unfortunately, this means the
information about the winning
lottery numbers remain
embedded in the pattern
and lost to us until after
the numbers are drawn.
If your name appears
below, you got this right
and described your reason well.
You guys should
email your names,
addresses, US t-shirt sizes,
so small, medium, large, etc.,
to pbsspacetime@gmail.com.
Also, let us know which of
these t-shirts you want.
We'll send it right out to you.
For the rest of
you, you can still
grab a "SpaceTime" t-shirt
of your very own via the link
in the description.
OK, that's the answer.
But there's still
time for a mini-rant
about the role of consciousness
in quantum mechanics.
The delayed choice
in this experiment
is whether or not to know the
path of the original photon
or whether to erase
that knowledge.
But don't take
this too literally.
We don't need to invoke
conscious knowledge
to explain the results.
If either detectors
A or B are triggered,
then there's an asymmetry
in the global wave function,
passing through one
slit versus the other.
And this can lead
to decoherence.
Admittedly, this
decoherence appears
to affect the wave function at
times before the apparent cause
of the decoherence.
But this doesn't end
up violating causality.
And so it's way less
out there than photons
somehow knowing
that in the future
some conscious mind
will know its path.
Frankly, it's all just so weird
and amazing, amazing enough
without inventing mystical
interpretations that somehow
give us psychic wave function
collapsing powers, as much
as we'd all like to
believe we have them.
Nonetheless, there
is a clue somewhere
in all this weirdness to
the fundamental workings
of spacetime.
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