from Space Website
My night musings often drift to deep truths of existence: thoughts on cosmos, consciousness, meaning (if any). I can't help it...
That's why I'm entranced by the idea of a multiverse, the theory that there are many universes, multiple universes, innumerable universes, perhaps an infinite number of universes.
But the same set of facts, theories and inferences that imply a multiverse also severely limit, and perhaps proscribe completely, humans' capacity to conduct high-grade scientific studies, experimental or observational, to detect a possible multiverse.
So is the search for a multiverse "science?"
It depends on what the word "science" means
I studied science (my doctorate is in brain research) because science discerns how the world works.
If there is any way to find agreement among disparate cultures and creeds, there's no way better way than through science. Some scientists say that the scientific method is the only way of knowing.
If science cannot know something, these scientists say, then that something is either not knowable or not worth knowing.
A multiverse, as we shall see, is a test case.
The essence of science - what science is actually doing - may seem obvious to scientists, but not to philosophers of science.
Bas van Fraassen is just such a philosopher of science, at San Francisco State University, and a professor of philosophy emeritus at Princeton University in New Jersey, and he is a strict empiricist, meaning that he believes knowledge qua knowledge must come directly from observation and data.
Van Fraassen said he is not a "scientific realist," meaning that he does not accept that the scientific criterion of success is "truth in every respect" or "truth, period."
He said he rejects the prevailing notion that science can penetrate deeper than,
He has argued that we must decouple what we observe from whatever underlying reality may be generating those observations.
In other words, there are (at least) two levels of reality:
Strict empiricism offers a more modest mission for science.
So does its philosophical cousin, anti-scientific realism, which rejects, for various reasons, the common-sense idea that what we perceive is what really exists (for example, doubting that reality is mind-independent).
Both strict empiricism and anti-scientific realism see an unbridgeable gap between deep reality and human cognition, because, like in a relay race, the "baton of information" is passed from one medium to another:
At each stage of that "information relay," argues the strict empiricist (and the anti-scientific realist), information is lost.
There are several gaps, which combine to constitute an overall, unbridgeable gap. As a strict empiricist, van Fraassen affirms only that which human beings can know for sure.
He allows only observations and models into his realm of certitude, but not the underlying realities that generate them.
Princeton physics professor J. Richard Gott described the boundaries of science in terms of what science can and cannot know.
Is there anything in the middle, so to speak, between what science can and cannot know?
The multiverse, stretching the limits of understanding
In answering that question, Gott pointed to a multiverse.
A multiverse, awesome if real, is indeed a test case for exploring the limits and boundaries of science.
Here's the question:
In response to my essay "Confronting the Multiverse - What 'Infinite Universes' Would Mean," Russia-born, Stanford-based cosmologist Andrei Linde challenged the skeptical, empirical position that postulating a multiverse is, in essence, not science.
South African cosmologist George Ellis sharply asserted that view in the journal Nature (Defend the Integrity of Physics - Scientific Method).
Ellis, who is well known for challenging the multiverse, argued that,
To make sure I understood what he meant by,
This oddly profound principle constrains theories of physics and cosmology by human existence, because humans must obviously exist if they are to observe the facts that they try to explain.
This seemingly trivial, tautological or even nonsensical claim is, depending on one's views, either a surprisingly powerful predictive and explanatory tool or an embarrassing abandonment of the scientific method and an excuse for failure.
Two Nobel Laureates in physics have offered me their diametrically opposing views on the anthropic principle.
Steven Weinberg at the University of Texas at Austin, one of the pioneers of this new way of thinking about science, said that assuming,
The reason, he said, was that,
In other words, if the cosmological constant, which is a kind of repulsive gravity, would be greater than a certain maximum amount, then its anti-gravity force would resist and overpower gravity, preventing gravity from forming agglomerated bodies (galaxies, stars, planets).
On the other hand, when asked his view of the anthropic principle, physicist David Gross at the University of California at Santa Barbara said,
In other words, in studying the energy density of empty space, the vacuum, why is the cosmological constant so astonishingly small but still not zero?
Linde said there are multiple problems in physics and cosmology, and only a multiverse can solve them, thus validating the theory of the multiverse as "science," even if justified in this new kind of way.
This theoretical finding was that there are (very roughly) 10500 different, theoretically feasible configurations or ways that string theory can generate different, theoretically feasible laws of physics (based on all the possible stable, geometrical or topological configurations of an infinitesimally small, higher-dimensional "manifold" that string theory proposes as the foundation of space and time and particles and forces).
Each one of this vast number of specific configurations or ways characterizes its own kind of universe - and perhaps doing so in reality innumerable times to define innumerable universes - all of which taken together compose the multiverse.
(This does not mean that the multiverse is inextricably tied to string theory, however elegant; there are other mechanisms that could generate multiple universes.)
Moreover, Linde claimed, this also means that the same facts that can serve as observational or experimental evidence in favor of a multiverse can simultaneously serve as observational or experimental evidence in favor of string theory.
In defense of his position [in recent correspondence following first publication of this essay], Linde stressed that no one has developed a better, more robust theory to explain the cosmological constant than the multiverse and string theory (not even after 18 years - the cosmological constant was discovered in 1998 with the stunning observation that the expansion of the universe was accelerating, not slowing down due to gravity as everyone had expected).
Linde admitted that this is an unusual way to think about science, and he cited Weinberg:
The failures of multiverse theory
With Linde's permission, I circulated his remarks to others quoted in my "Confronting the Multiverse" essay, and I received everyone's permission to post the remarks that follow.
In response, Ellis stated that Linde's argument requires three parts: experimental or observational facts to be explained, a viable theory that can explain these facts and no other theory that can work as well.
And Ellis claimed that for the multiverse, "there are problems with each part."
In summary, Ellis said arguments for the multiverse fail,
Pointedly, Ellis asserted that Linde’s multiverse-generating theories of cosmic inflation are ruled out or disfavored by recent observational data.
In response, Linde denied that "eternal chaotic inflation" is ruled out or disfavored by recent observational data, stressing differences among eternal chaotic inflation, chaotic inflation in general and its simplest version (all of which Linde discovered, or invented, depending on one's views).
Only inflation's simplest version, he said, is ruled out by recent observations.
Linde stressed that just because he rejects Ellis' arguments against the multiverse does not mean that he thinks the theory of the multiverse is complete.
After reviewing the contrasting positions, Rees wondered whether it is "inconsistent" that Ellis gave,
Personally, in my epistemology of a multiverse, as it were, I am influenced by Weinberg's simple statement:
Challenging current belief
Although in questioning the multiverse, Ellis is in the minority - certainly among contemporary cosmologists - I admire his challenge to current belief.
After all, that is what MIT physicist Alan Guth (the originator of cosmic inflation theory), Linde and others did in postulating cosmic inflation theory and multiple universes in the first place.
Ellis has made people think hard about the assumptions underlying the purported reality of multiple universes, which, if real, would radically expand the scope of existence.
Paul Davies, physicist and director of the Beyond - Center for Fundamental Concepts in Science at Arizona State University, stated that the multiverse theory can be indirectly tested in two ways.
In other words, Davies made a provocative point about the fit between the actual, measured value of (repulsive) dark energy and the theoretical maximum value that such (repulsive) dark energy could take, but still allow for human existence by not overpowering, and thus not nullifying, the gravitational attraction needed to form galaxies, stars and planets.
The tighter this fit, Davies said, the greater the consistency with a multiverse.
But, dare I say it, the same would also be true for consistency with a Design/Designer, would it not? ("The Multiverse and God" will be the topic of my third and final essay on the multiverse.)
Yet Davies challenged the multiverse by combining the implications of a multiverse with the so-called "Simulation Argument."
This draws on two premises or assumptions, that,
Given those two premises, then randomly chosen observers, like human beings, would most likely find themselves living in a simulated or "fake" universe (unless there are cosmic or technological "showstoppers" preventing whole-world simulations).
Davies argued that in a multiverse,
Let's unpack the argument and lay it out.
As a result,
Fake universes, Davies said,
And if the whole of physics is a fake, Davies said, then the whole argument for a multiverse collapses.
The reason is that while the multiverse argument proceeds from the physics humans have discovered in this universe, people cannot use this argument because it then leads, surprisingly, to the conclusion that this is a fake universe, with fake physics.
That, Davies claimed, is an internal contradiction of the multiverse theory.
The best way to avoid this circular contradiction, in my opinion, is by asserting that simulating whole worlds, especially the simulation of consciousness, is impossible - even impossible in principle, even with an infinite number of universes, a claim that causes its own set of problems.
Another way might be to suppose that any simulated laws of physics in simulated universes would likely be based on "real" laws of physics in the simulators' "real" universe. (But for this counterargument to work, there would need be no exceptions, none whatsoever - which in such a vast universe, I think, is a bar too high.)
At first, the Simulation Argument (the possibility that this universe is a fake) seems to have nothing to do with arguments for the multiverse, yet each, curiously, threatens the other.
Just as Davies showed how simulations would undermine the multiverse, a multiverse of infinite numbers of universes would play havoc with the Simulation Argument of this universe.
(The reason is that infinities mess up measurements and statistics, because when all things occur an infinite number of times, the relative occurrences of all things acquire a kind of strange equality.)
In support of a multiverse, philosopher John Leslie posed a novel argument.
That Creative Factor would be a principle, force, God - it doesn't matter what, he said.
Human beings seem hardwired to want to know things, all things; people want to push knowledge to its ultimate limits, plumb the depths of ultimate reality.