From: Inflated Expectations: A Cosmological Tale

Physicists are pretty good at coming up with memorable phrases to express their scientific disdain.

Einstein famously decreed, God does not play dice with the universe, as his justification for denying the inherently statistical nature of the world that quantum mechanics seemed to present.

Of course, the development of quantum mechanics was known to wreak considerable intellectual havoc among even its most significant contributors, such as Einstein. Erwin Schrödinger became so uncomfortable with the implications of his celebrated equation that he even came up with a notorious thought experiment involving a half-dead and half-alive cat to demonstrate the palpable absurdity of a standard interpretation of the theory, while plaintively summing up his view on quantum theory later on in his life with a pithy, I don’t like it, and I’m sorry I ever had anything to do with it.

Not all such dismissive remarks were specifically geared towards quantum mechanics, however. Perhaps the most notorious physics put-down is attributed to Wolfgang Pauli, who was said to have summarily rejected the work of a young physicist that was put before him by archly declaring, It is not even wrong.

Pauli’s meaning, it seems reasonable to conclude, is that the young physicist’s work was not only incorrect, it couldn’t even be coherently expressed in such a way as to be clearly and explicitly falsified. For falsification, too, is a form of scientific progress — albeit of a much less triumphant sort — that sometimes paves the way for deeper and more accurate theories.

Enter Paul Steinhardt, the Albert Einstein Professor and Director of the Center for Theoretical Science at Princeton University. Paul is a remarkably broad theoretical physicist who has made singular contributions to both cosmology and condensed matter physics. Among cosmologists he is perhaps best known for his seminal work in the early 1980s, together with Alan Guth and Andrei Linde, that led to the establishment of the theory of cosmic inflation as the primary paradigm of modern cosmology.

These days, however, Paul has decidedly broken ranks with his erstwhile inflationary colleagues, consistently drawing attention to the fact that there are deeply unsettling aspects of the theoretical framework of inflationary cosmology that should give all of us serious pause.

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Howard Burton in conversation with Paul Steinhardt, Princeton University

“Instead of driving the universe the way we had hoped from some random, initial state into a common, final condition consistent with what we observe, in fact the story of inflation is the following: it’s very hard to start; and if you do manage to start it, it produces a mess — what we call a “multiverse” — consisting of an infinitude of patches of possible, cosmic outcomes.”

Given the propensity of today’s theorists to invoke the notion of infinity, the reader might well be excused for not appreciating the seriousness of this problem. But this, Paul explains, is hardly the sort of thing to be swept under the rug, as it implies that, since any outcome is possible, there is no conceivable way we might one day be able to rule out the theory, even in principle.

Even worse still, however, sweeping it under the rug is precisely what many of his colleagues seem very much determined to do.

“I’ve had this discussion where I’ll say, ‘Well, what do you think about the multiverse problem?’ and they reply, ‘I don’t think about it.’

“So I’ll say, ‘Well, how can you not think about it? You’re doing all these calculations and you’re saying there’s some prediction of an inflationary model, but your model produces a multiverse — so it doesn’t, in fact, produce the prediction you said: it actually produces that one, together with an infinite number of other possibilities, and you can’t tell me which one’s more probable.’

“And they’ll just reply, ‘Well, I don’t like to think about the multiverse. I don’t believe it’s true.’

“So I’ll say, ‘Well, what do you mean, exactly? Which part of it don’t you believe is true? Because the inputs, the calculations you’re using — those of general relativity, quantum mechanics and quantum field theory — are the very same things you’re using to get the part of the story you wanted, so you’re going to have to explain to me how, suddenly, other implications of that very same physics can be excluded. Are you changing general relativity? No. Are you changing quantum mechanics? No. Are you changing quantum field theory? No. So why do you have a right to say that you’d just exclude thinking about it?’

“But that’s what happens, unfortunately. There’s a real sense of denial going on.”

Dogmatic denial is not terribly good for science. In fact, it could well be regarded as precisely the sort of closed-minded, unreflective attitude that the modern scientific temperament has emphatically, and so successfully, struggled against for centuries.

ut it’s not just a question of scientific stubbornness. Because theorists unwilling to grapple with inflation’s “multiverse problem” aren’t simply resolutely clinging to their theory despite any objective observed support for it. As Paul points out, they are clinging to their theory independent of any observed support for it.

Take the case of the reported findings of the BICEP2 experiment.

In March 2014 it was announced that BICEP2 had found a signal that was declared to have resulted from primordial gravitational waves consistent with inflationary theory, leading many to immediately crow that this result was irrefutable proof of inflationary theory.

A few months later, however, the signal was clearly identified with something quite different (dust within our own galaxy). Despite this observational about-face, however, proponents of inflation remain strikingly — and depressingly — undeterred.

“So you would think, If you just declared victory on the basis of the discovery of them, doesn’t that mean that you have to declare defeat on the fact that you didn’t see them?

“And the immediate response of the proponents of inflation was, ‘Absolutely not. Our theory is flexible enough that we can do that too. And we immediately got a litany of papers saying, Here’s how we’ll do that’.

“So you might well ask, Is there anything you could observe that would tell you that inflation is wrong?

“And, again, for many of the leading proponents of the field, the way they answer that question is to say, ‘No. Inflation is so flexible that no test or combination of tests can possibly disprove it’.

“In fact, in their view it has three degrees of flexibility: there are initial conditions that I’m allowed to fiddle with, parameters that I’m allowed to fiddle with, and then a multiverse that I’m allowed to fiddle with. So according to them it’s super-flexible.

“And my reaction to that is, ‘Okay, then, doesn’t that mean that you concede?

“And their response is, ‘No, what’s wrong with that?’”

What’s wrong, Wolfgang Pauli would dismissively inform us, is that it’s not even wrong.

This is the introduction written by Howard Burton of the book, Inflated Expectations: A Cosmological Tale, which is based on an in-depth, filmed conversation between Howard and Paul Steinhardt, the Albert Einstein Professor in Science and Director of the Center for Theoretical Science at Princeton University.

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The book is broken into chapters and includes questions for discussion at the end of each chapter. The book is also available as part of the 5-part Ideas Roadshow Collection called Conversations About Astrophysics & Cosmology which also features Roger Penrse, Scott Tremaine, Rocky Kolb and Justin Khoury.

Visit the dedicated page for Paul Steinhardt on Ideas On Film: https://ideas-on-film.com/paul-steinhardt/. On our Ideas On Film YouTube channel you can watch a clip from the filmed conversation: https://youtu.be/2s1V0gjmCmk.

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