In
a recent TED talk entitled “Have We Reached the End of Physics?”
the particle physicist Harry Cliff talks about two astonishingly
fine-tuned numbers that are fundamental to the observed structure of
our universe. He repeatedly calls these “dangerous numbers.” This
is a very strange description, because as the transcript of the talk
makes clear, the numbers have just the right values needed for
creatures like us to exist. So why use the word “dangerous”
to describe them? Given the facts Cliff discusses, it might be more
appropriate to use the term “providential” to describe these
numbers.
The
first number Cliff discusses is the value of the Higgs field, which
Cliff describes as a “cosmic energy field.” At 4:05 in the talk,
Cliff says this about the Higgs field.
But there is
something deeply mysterious about the Higgs field. Relativity and
quantum mechanics tell us that it has two natural settings, a bit
like a light switch. It should either be off, so that it has a zero
value everywhere in space, or it should be on so it has an absolutely
enormous value. In both of these scenarios, atoms could not exist,
and therefore all the other interesting stuff that we see around us
in the universe would not exist. In reality, the Higgs field is just
slightly on, not zero but 10,000 trillion times weaker than its fully
on value, a bit like a light switch that's got stuck just before the
off position. And this value is crucial. If it were a tiny bit
different, then there would be no physical structure in the universe.
This
is an extreme case of fine-tuning. Physicists were so bothered by
this case of fine-tuning that they spent innumerable hours (plus
countless tax dollars) working on a very ornate theory called
supersymmetry, designed mainly to explain away this particular case
of fine-tuning. But the theory is really just one of those “rob
Peter to pay Paul” affairs, as it requires the existence of a whole
set of undiscovered particles, the existence of which would be just
as big a case of fine-tuning as the fine-tuning that the theory tries
to explain away. So far, as Cliff notes, the giant particle
accelerator known as the Large Hadron Collider has failed to confirm
the predictions of supersymmetry, leaving it in a state that one
commentator has described as a deathbed state.
The
second of Cliff's two “dangerous numbers” is the degree of dark
energy in the universe. Dark energy is believed to be an energy
within empty space that is causing the universe to accelerate. Cliff
describes the following disagreement between theory and observations
(which is actually the biggest such disagreement ever):
Now, if you use
good old quantum mechanics to work out how strong dark energy should
be, you get an absolutely astonishing result. You find that dark
energy should be 10 to the power of 120 times stronger than the value
we observe from astronomy. That's one with 120 zeroes after it. This
is a number so mind-bogglingly huge that it's impossible to get your
head around. We often use the word "astronomical" when
we're talking about big numbers. Well, even that one won't do here.
This number is bigger than any number in astronomy. It's a thousand
trillion trillion trillion times bigger than the number of atoms in
the entire universe.
You
can get a better grip on this idea if you understand that quantum
mechanics predicts that ordinary empty space should be teeming with
mass-energy, so much so that each cubic meter of empty space should
be denser than steel. In fact, the quantum mechanics prediction is
that each thimble-sized unit of space should have more mass-energy
than if the entire Earth were packed into it.
So
why do we live in a universe so different from that type of universe?
Physicists basically have no clue.
Ever since the invention of the atomic bomb we have enthroned our
theoretical physicists as some kind of towering geniuses, but in this respect it
seems that they are really like someone who predicts this as the
score of the next Super Bowl:
Carolina
Panthers: 345,564,456,786,123,523,236,234,845
Denver
Broncos: 24
Describing
the multiverse theory, Cliff offers this wobbly explanation (perhaps
just summarizing the thoughts of others):
What if all of
these 10 to the 500 different possible universes actually exist out
there somewhere in some grand multiverse? Suddenly we can understand
the weirdly fine-tuned values of these two dangerous numbers. In most
of the multiverse, dark energy is so strong that the universe gets
torn apart, or the Higgs field is so weak that no atoms can form. We
live in one of the places in the multiverse where the two numbers are
just right. We live in a Goldilocks universe.
This
is basically an “anthropic principle” explanation, the idea that
we can explain some lucky number in our universe simply on the
grounds that if it didn't have such a number, we wouldn't exist. But
unless some willful causal agent is introduced within such an
explanation, such an explanation is untenable, because you can't
naturally explain something merely by referring to something else
that came eons later. Causes come before effects, not after them.
If event X occurred millions of years after effect Y, we cannot
explain effect Y merely by referring to event X. The universe's
level of dark energy and the numerical value of the Higgs field are
effects that existed billions of years before life appeared, and we
can't explain such effects naturally merely by referring
to something that came eons later (the appearance of life).
I
may add that the multiverse does nothing to fix the bad reasoning of
trying to explain an effect by referring to something that came eons
later. Nor would the existence of a multiverse make it more likely
that our particular universe would have the right numbers by lucky
coincidences, since the probability of success on any one random
trial is not increased by increasing the number of random trials.
Moreover, while
Cliff uses the statement “suddenly we can understand the weirdly
fine-tuned values of these two dangerous numbers,” his
previous statements contradict that. For based on what he said
earlier, a dark energy level of the type we have (very, very low)
should not just be incredibly improbable but actually impossible.
For quantum mechanics predicts (according to Cliff) that dark energy
should be billions of trillions of quadrillions of quintillions of
times greater than it is. So apparently according to quantum
mechanics, the chance of a universe such as ours is not just very,
very low, but actually zero.
Multiverses
actually are not of any value in explaining the incredibly
improbable, and they certainly are of no value in explaining a
reality that seems to have a natural probability of zero.
See here for more on the "vacuum catastrophe" discussed by Cliff.
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