Sinister Security: Origin of the UNiverse

New Calculation Could Spell Trouble For a Popular Theory of the Universe's Origin

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The universe began. But what did it begin from? What did it begin into? We know it began by expanding rather quickly, and ended up with lots of big galaxies made from little particles. But what happened before then? What were the laws of physics like when it all started?

Famous physicists James Hartle and Stephen Hawking proposed some answers to some of these problems several decades ago. A new paper from another team of physicists analyzed Hawking and Hartle’s popular interpretation of the geometry of the big bang, and ran into some trouble. These results shed light on a problem in the universe’s beginning; a new hurdle that any future theories will need to hop over.

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“We tried to do the calculation more rigorously and obtained this different solution. This theory we use sheds some new light on this existing idea and shows that it might not work the way [we] expected it to work.” Job Feldbrugge, a resident PhD student at the Perimeter Institute, told Gizmodo.

Researchers usually try to understand the beginning of the universe by taking a look at Einstein’s laws of gravity, called general relativity, and playing them in reverse. Eventually, you should get to a point long ago in which the universe was really tiny. But questions arise as to what the baby universe looked like, including whether it was small enough to obey the laws of quantum mechanics, which seems to govern the way that the smallest particles like atoms and photons behave.

There are a few ways our present universe could have started. Maybe, Hawking and Hartle thought, this condensed universe was just one point in space with a special quantum state, a so-called wave function that described the whole thing with quantum mechanics. Then, time started. Philosophy and religion require a lot more conversation for that statement, but math sort of just requires a pen and paper. This point-sized universe evolved based on the mathematics of general relativity with the initial probabilities of quantum mechanics built into its structure.

The teeny, random energy fluctuations in space would then, through a quick-expanding process called inflation, turn into the large-scale density differences we see in our universe today, with galaxies and voids. Hawking and Hartle’s theory is one of several ways to account for the start of the universe without a singularity, a point of zero volume and infinite mass that doesn’t make a whole lot of sense. Other ideas, like the ones posed by Tufts cosmologist Alexander Vilenkin, don’t mind this initial singularity.

But this new paper, published recently on the arXiv physics preprint server, introduces a problem. When running Hawking and Hartles’ as well as Vilenkin’s, math, the new team didn’t get the teeny quantum fluctuations required to create today’s universe. Instead, those fluctuations are gigantic, and create a universe complete unlike our own.

“The calculation we do results in violent gravitational waves after the Big Bang. It couldn’t result in a universe like today’s. The calculations conflict with the stuff we see.” said Feldbrugge—enormous fluctuations in the shape of spacetime itself. Hartle wasn’t so concerned by Feldbrugge’s team’s results.

“In cosmology… we still have a very small amount of data compared to what we might hope to have. Therefore we do the best job we can, supplying the piece of the theory which is motivated by all of our observations and see how it does. Researchers can decide if they will pursue one of these [ideas] rather than another.” he told Gizmodo.

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He felt this new work is another attempt to turn the crank, offering more information and another mathematical pathway that researchers can pursue. His team has also published another recent paper, reviewing their own mathematics, and demonstrating why things still work. Still, Feldbrugge and his team’s math seem to show that a smooth beginning to the universe without some sort of singularity is “not an option.” Their math seems to directly dispute Hartle and Hawking’s.

Linking quantum mechanics and general relativity to explain the start of the universe is neither a new story nor a problem close to being solved. It’s one of the core things that theoretical physicists are trying to do, given its importance both for understanding the origin of the universe when both sets of laws applied at the same scale, and its importance in black holes, places where gravity is so strong that light can’t escape its pull.

But the main point is that Feldbrugge doesn’t think a universe beginning with the laws of quantum mechanics and relativity alone would create small fluctuations that result in a universe like ours—he thinks there has to be something else. “It’s not clear which solution will be the ultimate option,” he said.

Other physicists had varying opinions on the matter. Paul Steinhardt, physics professor at Princeton University, told Gizmodo that there are already alternative routes to go down to avoid the problems in the new paper, as well as some of the other complaints with the Hawking-Hartle model. This so-called no boundary model requires some mathematical workarounds to create a universe like ours.

“What’s the alternative? It’s a non-singular bounce,” he said, a model that he and Princeton theoretical cosmologist Anna Ijjas are working on, where a past universe collapses and then turns around into our own universe, all before having to worry about the effects of quantum mechanics.

I also reached out to Sabine Hossenfelder, Research Fellow at the Frankfurt Institute for Advanced Studies, who wasn’t entirely convinced by the new results.

“The only thing I conclude is that we didn’t know how the universe began before the paper was written and we still don’t know how it began after it was written.” she wrote in an email.

She said that theorists take math very seriously, and are performing these calculations for times and spaces far beyond what telescopes can see. The only way to really tell what’s going on is with experiments, she said. Today, most of these theories can be proven or disproven by observing the oldest light to reach us, the cosmic microwave background. Researchers all hope that their theories’ implications will turn up as specific signatures in this data.

Can Feldbrugge and the team’s work be tested? They’re really only at the beginning stages. And then there’s the problem of black holes, which also must obey the laws of general relativity and quantum mechanics simultaneously. Figuring them out “is certainly on our to do list,” he said.

Obviously, all of this work is going to take a very, very long time. Scientists need to end up with a universe that acts like ours, but, said Hartle, “the details are up in the air.”

[Gizmodo]

Stephen Hawking and 32 Top Physicists Just Signed a Heated Letter on The Universe's Origin

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For centuries, people have puzzled over how our Universe began. But the heat just got turned way up on a debate that's quietly been raging between cosmologists, with 33 of the world's most famous physicists publishing a letter angrily defending one of the leading hypotheses we have for the origin of the Universe.

The letter is in response to a Scientific American feature published back in February, in which three physicists heavily criticised inflation theory - the idea that the Universe expanded just like a balloon shortly after the Big Bang. The article went as far as claiming that the model "cannot be evaluated using the scientific method" - the academic equivalent of saying it isn't even real science.

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In response, 33 of the world's top physicists, including Stephen Hawking, Lisa Randall, and Leonard Susskind, have fired back by publishing their own open letter in Scientific American. The Cliff's note version is this: they're really angry.

Inflation theory was first proposed by cosmologist Alan Guth, now at MIT, back in 1980. It's based on the idea that a fraction of a second after the Big Bang, the Universe expanded rapidly, spinning entire galaxies out of quantum fluctuations.

"By the time it slowed down, what had been a tiny, quivering quantum realm was stretched out until it looked smooth and flat, save for speckles of denser matter that later became galaxies, stars, and planets," writes Joshua Sokol for The Atlantic.

In the following years, Guth's original idea was improved and updated by Stanford physicists Andrei Linde, and they've since spent their careers refining the inflation model - which has become the leading theory for how the Universe was born.

In fact, most of us were taught inflation theory at high school and university when discussing the Universe's origins. Guth and Linde, along with cosmologists David Kaiser and Yasunori Nomura, were the ones who recruited the other 29 signees behind this week's letter.

Interestingly, one of Guth and Linde's former colleagues, physicist Paul Steinhardt, is part of the trio they're rallying against. Guth, Linde, and Steinhardt all shared the prestigious Dirac prize "for development of the concept of inflation in cosmology" back in 2002.

But in the years since, Steinhardt has gone rogue, and has become an active critic of inflationary theory. He was one of the authors of Scientific American's February feature, originally titled "Pop goes the Universe", along with Princeton physicist Anna Ijjas, and Harvard astronomer Abraham Loeb.

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That article highlighted recent research into the cosmic microwave background, which doesn't match up with the predictions of inflationary theory. It also criticised the fact that inflation would have generated primordial gravitational waves, which have never been found.

"The data suggest cosmologists should reassess this favoured paradigm and consider new ideas about how the universe began," summarises an In Brief wrap up of the article.

That criticism in itself wasn't a huge deal - these kinds of arguments are healthy in the science world. But what really pissed off Guth, Linde, and the 31 other signees, was the suggestion that inflationary theory couldn't actually be tested in the first place, and therefore wasn't really science.

"They [made] the extraordinary claim that inflationary cosmology 'cannot be evaluated using the scientific method' and go on to assert that some scientists who accept inflation have proposed 'discarding one of [science's] defining properties: empirical testability,' thereby 'promoting the idea of some kind of nonempirical science'. We have no idea what scientists they are referring to. We disagree with a number of statements in their article, but in this letter, we will focus on our categorical disagreement with these statements about the testability of inflation." the physicists write in their open letter.

Their argument is that inflation theory is based on many models, and there's no illusion that all of these models are correct. Over the past 37 years, some of the models have made correct, testable predictions - including the average mass density of the Universe, and its flat shape. Many are still unresolved. But either way, these models are all testable, which means they're proper science, and they can be proven or disproven depending on the evidence we find in the coming years.

Ryan F. Mandelbaum has done incredible coverage of this feud over at Gizmodo, and points to a blog entry by Sean Carroll, one of the physicists who signed the letter, on the controversy:

"We judge theories by what predictions they make that we can test, not the ones they make that can't be tested. It's absolutely true that there are important unanswered questions facing the inflationary paradigm. But the right response in that situation is to either work on trying to answer them, or switch to working on something else (which is a perfectly respectable option). It's not to claim that the questions are in principle unanswerable, and therefore the field has dropped out of the realm of science."

The authors of the original article have since responded to the letter with their own extended FAQ on the debate. And they maintain their position - that inflation was once testable, but "what began in the 1980s as a theory that seemed to make definite predictions has become a theory that makes no definite predictions".

Which takes us right back to where we started... some cosmologists have publicly slammed inflation theory, and others have angrily responded.

Unfortunately there's no neat resolution to this debate on the horizon, with both sides standing pretty firm. The one thing they both agree on is the fact that inflation theory isn't perfect, and we should all keep an open mind about what really happened at the birth of our Universe as new data comes in. Or as Guth told Mandelbaum in the ultimate mic drop when asked what would happen next: "I think we'll all continue on with our research."

You can read the original article here, the responding open letter here, and the original authors' response here.

Sinister Security

New Calculation Could Spell Trouble For a Popular Theory of the Universe's Origin

Stephen Hawking and 32 Top Physicists Just Signed a Heated Letter on The Universe's Origin

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