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In defence of dark energy

Nobel Laureate and dark matter pioneer answers critics

2nd March 2023
| Winner of the 2019 Nobel Prize in Physics, and dark matter pioneer. He is the Albert Einstein Professor in Science, Emeritus, at Princeton University
2,075 words
Read time: approx. 10 mins

The evidence is that Dark Energy is responsible for the rate of expansion of the universe. The name makes it sound like a spooky force, but, in fact, it’s the cosmological constant, Λ, that Einstein added to his theory of gravity back in 1917. Einstein regretted it, but we have been forced to put Λ back in the theory to fit the evidence. There is theoretical backing of a sort from quantum theory, which also predicts the presence of a cosmological constant, Λ, but with a value that is far off what we need. Finding a way to unify the predicted value of Λ by quantum theory, and the observed value of Λ from the expanding universe, would be a great discovery. But even the most sophisticated theory is constrained by observational evidence, which always will be imperfect and incomplete, and hence our theories always will be an approximation, never an account of ultimate reality, argues James Peebles. 

 

The standard theory for explaining the expansion of the universe from a hot dense state requires the presence of Einstein's cosmological constant. The usual symbol for it is the Greek Λ, and today Λ is more commonly known as Dark Energy. Maybe the name is an improvement, but nothing else has changed. Our well-tested theory of the expanding universe needs something that acts like Λ, but we still do not know how this Λ fits in with our standard physics.

Our model of the universe has been falsified.dc SUGGESTED READING Our model of the universe has been falsified By Pavel Kroupa

It has been known since the 1930s that quantum physics naturally predicts the presence of a cosmological constant, Λ, but the predicted value is absurdly large. A quarter of a century ago, when we had much less evidence of how the universe is evolving, we tended to say that since the quantum estimate of Λ is clearly wrong, the only natural alternative is that Λ is zero. Einstein would have agreed with this hopeful argument; he regretted adding this term to his new theory of gravity, the general theory of relativity. But the accumulated evidence now makes a compelling case that we must learn to live with Λ, Dark Energy.

James Peebles
2nd March 2023

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Bud Rapanault 15 March 2023

This is quite a piece of work. It claims to be a defense of dark energy but it is in fact just a limp special pleading on behalf of the Standard Model of Cosmology, filled out with vague philosophical musings and a diversionary nod to actual physics (Maxwell's theory electromagnetism). Apparently this is the best the SMC's defenders can do in response to the recent claim (published here at IAI) by the astrophysicist Pavel Kroupa that the SMC has been falsified.

If you want to grasp just how deeply the contagion of mathematicism has settled into the scientific academy this article is a good place to start. The hyper-advanced model-fitting exercises that pass for science in the theoretical physics community are on full display:

"... I introduced it [dark matter] in 1982 to allow a more comfortable fit of the expanding universe theory to what we knew then."

"... I reintroduced the old idea of including the value of Λ [dark energy]. As before, it was meant to get the theory to continue to fit the growing evidence."

The terms "more comfortable fit" and "continue to fit" are just ways of eliding the fact that the standard model of the time did not fit the observations, Note the illogical progression from the simple fact that the General Relativity/Expanding Universe model was being contradicted by the observational evidence to the supposition that it was physical reality that was at fault, not the mathematical model itself. James Peebles proudly lays claim to this bit of intellectual jujitsu, correcting the model's failings by the ad hoc, implicit addition of dark matter and dark energy to physical reality.

The fact that physical reality has subsequently failed to provide any empirical evidence for the existence of Peebles' "dark sector" might give pause to a scientist but it is not a problem for a mathematicist. Mathematicists are those who adhere to the ancient, philosophical belief that math underlies and determines the nature of physical reality. There is no scientific basis for that belief whatsoever but it has, unfortunately, become the default operating paradigm of the theoretical physics community. This allows Pebbles to make this preposterous special pleading for dark matter and by extension, all of the SMC's undetectable entities and events:

"Perhaps Dark Matter will never be detected, apart from its gravitational effects. Even so, that would not be an argument against its existence. It would instead exemplify the obvious fact that we are limited in what we can hope to discover."

And there you have the so-called crisis in physics reduced to the fundamental error of mathematicism. While science may be restricted to studying the empirical realm of those things that can be directly observed, detected, and measured, mathematicists hold esoteric knowledge of things that lie beyond the range of science in the verdant, boundless realm of the human imagination lying between the mathematicists' ears.

Unfortunately for the mathematicist project, it is a well known and oft demonstrated fact that the human imagination is not a reliable guide to the nature of physical reality. It does give rise to amusing metaphysical speculations of course, like how many angels can dance on the head of a pin or how much vacuum energy lies between the SMC guess and QFT (Quantum Field Theory) guess?

Dark matter and dark energy are the angels and devils of the modern mathematicist's worldview. They are, by Peebles' account, unfalsifiable conjectures of mathematical convenience. They are beliefs unconnected to physical reality; they are wholly imaginary entities that do not exist in the realm of scientific knowledge. One can make the same argument against the entirety of the SMC: it is a set of mathematicist beliefs about the nature of physical reality that lack any empirical basis in physical reality. Professor Kroupa and Moritz Haslbauer in conclusion to their IAI piece, sum up the situation nicely:

"Thus, rather than discarding the standard cosmological model, our scientific establishment is digging itself ever deeper into the speculative fantasy realm, losing sight of and also grasp of reality in what appears to be a maelstrom of insanity."