For
several decades scientists have discovered more and more examples
suggesting our universe is seemingly tailor-made for life. A list of
many examples is discussed here. One dramatic example is the fact
that even though each proton in our universe has a mass 1836 times
greater than the mass of each electron, the electric charge of each
proton matches the electric charge of each electron exactly, to 18 decimal places, as discussed here (the only difference being that one is
positive, the other negative). Were it not for this amazing
coincidence, our very planet would not hold together. But scientists
have no explanation for this coincidence, which seems to require luck
with a probability of less than 1 in 1.000,000,000,000,000,000. As wikipedia
states, “The
fact that the electric
charges of electrons
and protons seem to
cancel each other exactly to extreme precision is essential for the
existence of the macroscopic world as we know it, but this important
property of elementary particles is not explained in the Standard
Model of particle physics.”
Wishing
to cleanse their minds of any suspicions that our universe may not be
the purely accidental thing they imagine it to be, quite a few
materialists have adopted the theory of a multiverse. This is the
idea that there is a vast collection of universes, each very
different from the other. The reasoning is that if there were to be,
say, an infinite number of universes, then we would expect that at
least one of them would have the properties necessary for intelligent
life, no matter how improbable it may be that such properties would
exist.
I will refer to such a collection of
universes as a varying-constants multiverse, since the concept is
that the fundamental constants of different universes in this
collection would vary. The fundamental constants are items such as Planck's constant, the gravitational constant, the speed of light, the proton charge, the electron charge, and the mass ratio of the proton and the electron.
The
question I will consider in this post is: is there any possible way
that such an idea of a varying-constants multiverse could be verified?
Why a Varying-Constants Multiverse Could Not be Verified Through Telescopic Observations
You
might think that we could verify the idea of a varying-constants
multiverse by long-range telescopic observations. You can imagine
scientists building some giant telescopes a thousand times more
powerful than any ever built. If such telescopes were to allow
scientists to look a thousand times farther than they ever looked
before, then you might guess that one day scientists might be able to
see other regions of space where the constants of nature differ. You
might, for example, imagine that scientists looking as far as
possible in one direction might see some distant area where the speed
of light was much higher, and scientists looking as far as possible
in some other direction might see some distant area where the
gravitational constant was much different than it is on Earth.
But
nothing of the sort has happened, and there is a reason why it cannot
ever happen. The reason is that because of the limit set by the speed
of light, whenever we look very far away in space, we are looking
back in time. So when we look 10 billion light-years away (near the
current observational limits of our telescopes), we are looking 10
billion years back in time. Scientists say that our universe began in
the Big Bang about 13 billion years ago. So we have a built-in limit
as to how far our telescopes will ever be able to look. We can never
hope to observe anything, say, 16 billion light years away, simply by
building more and more powerful telescopes.
Our
most powerful telescopes (such as the Hubble Space Telescope) can
look almost as far as humans will ever be able to see with
telescopes, which is about 13 billion light years. There is no chance
at all that by looking a little farther we will be able to see some
sign of another universe. As we approach the observational limit of
about 13 billion years, we are looking back a little more to the
beginning of our own universe. Scientists say that various aspects
of the very early universe and the Big Bang (such as what is called
the recombination era) act as a barrier that will forever block us
from observing all the way back to the time of the universe's birth
in the Big Bang.
So
there is no hope at all of being able to verify any theory of a
varying-constants universe just by looking farther and farther out in
space. But some have suggested two other ways in which we might be
able to lend credence to a multiverse theory by telescopic
observations: (1) by observing strange, unexplained motions of parts
of our universe; (2) by finding evidence of previous cycles of our
universe.
The
first of these involves the idea that we might be able to see that
some fraction of our universe is moving around in an unexplained way,
possibly because of gravitational influences by some nearby universe.
Such an observation is theoretically possible, but would not actually
be any observational support for the idea of a multiverse with
varying constants. If we observed such an unexplained motion, it
would best be explained by postulating new factors and physics within
our observed universe. Even if we were to be forced to conclude that
our universe is being gravitationally tugged by some other universe,
that would at best be support for the idea that our universe has a
“sister universe,” rather than the almost infinitely more
complicated idea that there are a vast collection of universes.
Moreover, such an observation would provide no support for any idea
that other universes have a variety of different physical constants.
The
same thing can be said about the idea of finding evidence that our
universe had previous cycles. If such evidence were found, it might
lead us to think that the universe existed before the Big Bang, and
that the universe is older than 13 billion years. But such evidence
would not give any basis for believing in anything like a
varying-constants multiverse. If our universe had previous cycles,
there is no reason to think that its fundamental constants such as the proton charge would change from one
cycle to the next. Science knows of no mechanism by which the
fundamental constants of the universe could change (here I exclude
the Hubble constant, a measure of the universe's expansion rate,
which is not really a fundamental constant).
Could
we ever verify the theory of a varying-constants multiverse by
verifying the theory of cosmic inflation, the idea that the universe
underwent an exponential expansion during part of its first instant?
No. I may first note that the prospect of being able to verify any
theory of cosmic inflation is far dimmer than many now think. It
is very doubtful that the current technique being pursued (based on
looking for b-mode polarization) will ever provide any real verification.
There are many sources of b-mode polarization that are not caused by
inflation (gravitational lensing, dust, synchrotron radiation, and
others), so trying to find a fingerprint of inflation is like trying
to extract a DNA sample from a bandage that was passed around and shared by ten different people with bleeding wounds.
But
even if scientists were to confirm a theory of cosmic inflation, that
would not verify any theory of a varying-constants multiverse. For
one thing, while some versions of the inflation theory imagine inflation
producing multiple bubbles of space that might be called other
universes, we would have no way of knowing whether such other bubbles
of space had ever formed, as they would be forever unobservable. More
importantly, we would have no license for assuming that such bubbles
of space would be universes with fundamental constants that differed
from our own. If one universe produced bubbles of space that branched
off to become spatially separated from that universe, the
most natural assumption is that such “universes” (or, more
properly, other regions of the same universe) would have the same
fundamental constants as their parent universe, particularly since science knows of no mechanism by which one universe could somehow produce a different universe with different fundamental constants.
There
is still one other technique that might be proposed for verifying the
idea of a varying-constants multiverse: the technique of actually
launching a mission into another universe. One
can imagine some amazing machine that might allow us to travel from
our universe to a different universe. In theory, if mankind or its
successors were to launch several trips to other universes, and
verify that they had different fundamental constants, that might
verify the idea of a varying-constants universe.
But
there are huge problems with such an idea. The first is that science
offers no clue as to how we ever could travel to another universe.
The idea seems like pure fantasy, a thousand times more fanciful and
extravagant than the farfetched idea of instantly traveling to
another star through a space-time wormhole.
The
second reason is that if we were somehow to create some machine
capable of traveling to another universe, there is no reason to think
that it would be capable of traveling back to our universe or sending
signals back to our universe (either of which would be necessary for
any real verification to occur).
The
third reason is that if we were somehow able to create a machine that
traveled to another universe, it would still be all but impossible
for such a device (or people or robots traveling in it) to verify
that the other universe had a set of fundamental constants different
from ours. The measurement of our universe's fundamental constants
has taken decades of work by scientists around the world. There's no
reason to think that a machine transported to another universe would
be able to verify that the fundamental constants of that universe
were different.
The
fourth reason is that if one imagines the scenario of a varying
constants universe (many universes, each with random fundamental
constants), there would be an overwhelmingly high likelihood
(such as 99.999999999%) that any machine transported to such a universe would
be instantly destroyed, along with any robots of humans that came
along for the ride.
To
understand this point, you have to consider the astonishingly high
degree of fine-tuning that allows stable matter to exist in our
universe. In his book The Symbiotic Universe, astronomer George
Greenstein says this
about the equality of the proton and electron charges: "Relatively
small things like stones, people, and the like would fly apart if the
two charges differed by as little as one part in 100 billion.”
There are quite a few other cases of fine-tuning required for the existence
of stable matter, including fine-tuning of the strong nuclear force.
So
if we then imagine a machine being transported to another universe
with random physical constants, we have to imagine the machine (and
any one inside it) being instantly destroyed as soon as it was
transported to another universe. With a 99.9999999% likelihood the
coincidences which allow for stable atoms and molecules in our
universe would not exist in such a universe. As soon as the machine
got over to the other universe, its atoms and molecules would split
apart, as the machine would (with overwhelming likelihood) no longer
be in a universe which favored the existence of atoms and molecules.
A recruiting poster from 4000 AD ?
Because of these various reasons, we can conclude that there is no substantial possibility that any machine could ever be transported to another universe to help verify the concept of a multiverse consisting of many universes, each with a different set of fundamental constants.
It seems that it is quite impossible to ever verify the theory that there are multiple universes with varying fundamental constants. The theory is neither falsifiable nor verifiable. Consequently, the theory is more of a metaphysical theory than a scientific theory, as all truly scientific theories can be either verified or falsified under some reasonable scenario.
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