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The Big Bounce: Why our universe might be eternal

When it comes to theories of the universe, the Big Bang theory is almost accepted as a fact. However, it's still uncertain, and some scientists believe that the universe didn't began with a bang, but a bounce.

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  • The Big Bang theory is treated as the de facto way the universe began, but it's had some issues.
  • One issue was that it could not describe how the universe became uniform and homogeneous, which is what we observe today.
  • Physicists tweaked Big Bang theory to accommodate this, but the Big Bounce theory can address these issues without too much tweaking.


Most of us are familiar with the standard narrative of how the universe began. There was an infinitely dense point of an infinite temperature with no size called a singularity. This singularity exploded, creating all the space, energy, and matter that we consider to be our universe in an event called the Big Bang. Between 10-36 seconds (that's 0.000000000000000000000000000000000001 seconds) and 10-32 seconds, space expanded exponentially, growing much, much larger in size. After this period, space continued to expand, but at a much slower rate, and eventually we see the universe that we observe today. This is the inflationary Big Bang theory, the most popular and broadly accepted theory of how the universe began. However, we have yet to prove this theory, and some think it doesn't paint an accurate picture.

Why we need inflation

A graph of the expansion of the universe. On the far left of this image, you can see the very brief moment of inflation that many physicists believe counterbalanced the randomizing effects of early quantum fluctuations.

Wikimedia Commons

Among these critics is Princeton physicist Paul Steinhardt, who actually contributed to the development of the theory described above, the idea that there was a moment of massively expanding space referred to as the inflationary epoch that quickly slowed down to the rate of expansion seen today. But including the inflationary epoch seems odd — why would there be this sudden change in the pace of expansion? It's actually something of an invention, a means of patching a troublesome quirk in the vanilla Big Bang theory.

"The Big Bang is not something that we really deeply understand, we have no theory of the Big Bang," says Steinhardt.

"But our notion is that it's some random, highly turbulent, quantum beginning from nothing to something. And so, it would leave a universe which is very random and distorted. Yet we don't observe that in the way the universe looks today. So we need some idea to fix that."

Today, when you zoom out far enough, the universe looks fairly flat and uniform — matter and energy are all fairly evenly distributed, and spacetime doesn't appear to have any curves. Inflation helped bridge the gap between the very random explosion of the singularity and the uniformity we see today — space expanded so rapidly that it smoothed out all the irregularities that would have occurred due to quantum effects during the Big Bang.

Does inflation cause more problems than it solves?

Despite helping to develop it, Steinhardt sees a few issues with the inflation model. For instance, those quantum effects that the inflation theory was supposed to deal with can actually create patches of the universe where inflation goes on forever. "The problem is," said Steinhardt in an interview with Nautilus, "due to the effects of quantum physics these patches are not all the same. The effects of quantum physics, when you include them properly, lead to a situation where some patches are like us, but some patches are not like us; and in fact, every conceivable possible outcome of the universe can occur if you look from patch to patch to patch and there's no particular reason why ours is more likely than any other." What Steinhardt is describing here is a multiverse, an infinite number of different universes with different rules. The one where we exist just so happens to have the right rules.

The trouble with this is that it almost seems like cheating. If inflation produces an infinite number of universes, then of course we would end up with the one we see around us; it doesn't really explain our specific universe. And for this reason, the inflation theory can't be disproved either — it predicts everything, and so makes no testable predictions. What if there were a simpler explanation?

Cue the Big Bounce

Instead of a Big Bang, with its attendant issues requiring the introduction of inflation, Steinhardt and other scientists have been toying with the idea of a Big Bounce. There are a variety of Big Bounce theories, but they essentially boil down to the idea that the universe is caught in a cycle where it expands after the Big Bang, then begins to contract. Some theories say that it contracts to the point of a singularity, where classical physics breaks down, and explodes again into a new Big Bang, while other theories suggest that the universe contracts to a point just above a singularity, where classical physics continue to apply.

But crucially, this process of contraction gives the universe time to become uniform throughout. When the bounce occurs, all matter is fairly uniform, becoming disordered over time. We currently live in a time when the universe is orderly, but it will become disorderly as time goes on. Once it begins contracting, the universe becomes increasingly orderly again. As it contracts further and further, matter and energy become more evenly distributed throughout the universe. Things flatten out and become more homogeneous as the next bounce approached. It could be that our universe has no definite beginning and will have no definite end — it could just bounce eternally.


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Human brains remember certain words more easily than others

A study of the manner in which memory works turns up a surprising thing.

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Mind & Brain
  • Researchers have found that some basic words appear to be more memorable than others.
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Cognitive psychologist Weizhen Xie (Zane) of the NIH's National Institute of Neurological Disorders and Stroke (NINDS) works with people who have intractable epilepsy, a form of the disorder that can't be controlled with medications. During research into the brain activity of patients, he and his colleagues discovered something odd about human memory: It appears that certain basic words are consistently more memorable than other basic words.

The research is published in Nature Human Behaviour.

An odd find

Image source: Tsekhmister/Shutterstock

Xie's team was re-analyzing memory tests of 30 epilepsy patients undertaken by Kareem Zaghloul of NINDS.

"Our goal is to find and eliminate the source of these harmful and debilitating seizures," Zaghloul said. "The monitoring period also provides a rare opportunity to record the neural activity that controls other parts of our lives. With the help of these patient volunteers we have been able to uncover some of the blueprints behind our memories."

Specifically, the participants were shown word pairs, such as "hand" and "apple." To better understand how the brain might remember such pairings, after a brief interval, participants were supplied one of the two words and asked to recall the other. Of the 300 words used in the tests, five of them proved to be five times more likely to be recalled: pig, tank, doll, pond, and door.

The scientists were perplexed that these words were so much more memorable than words like "cat," "street," "stair," "couch," and "cloud."

Intrigued, the researchers looked at a second data source from a word test taken by 2,623 healthy individuals via Amazon's Mechanical Turk and found essentially the same thing.

"We saw that some things — in this case, words — may be inherently easier for our brains to recall than others," Zaghloul said. That the Mechanical Turk results were so similar may "provide the strongest evidence to date that what we discovered about how the brain controls memory in this set of patients may also be true for people outside of the study."

Why understanding memory matters

person holding missing piece from human head puzzle

Image source: Orawan Pattarawimonchai/Shutterstock

"Our memories play a fundamental role in who we are and how our brains work," Xie said. "However, one of the biggest challenges of studying memory is that people often remember the same things in different ways, making it difficult for researchers to compare people's performances on memory tests." He added that the search for some kind of unified theory of memory has been going on for over a century.

If a comprehensive understanding of the way memory works can be developed, the researchers say that "we can predict what people should remember in advance and understand how our brains do this, then we might be able to develop better ways to evaluate someone's overall brain health."

Party chat

Image source: joob_in/Shutterstock

Xie's interest in this was piqued during a conversation with Wilma Bainbridge of University of Chicago at a Christmas party a couple of years ago. Bainbridge was, at the time, wrapping up a study of 1,000 volunteers that suggested certain faces are universally more memorable than others.

Bainbridge recalls, "Our exciting finding is that there are some images of people or places that are inherently memorable for all people, even though we have each seen different things in our lives. And if image memorability is so powerful, this means we can know in advance what people are likely to remember or forget."

spinning 3D model of a brain

Temporal lobes

Image source: Anatomography/Wikimedia

At first, the scientists suspected that the memorable words and faces were simply recalled more frequently and were thus easier to recall. They envisioned them as being akin to "highly trafficked spots connected to smaller spots representing the less memorable words." They developed a modeling program based on word frequencies found in books, new articles, and Wikipedia pages. Unfortunately, the model was unable to predict or duplicate the results they saw in their clinical experiments.

Eventually, the researchers came to suspect that the memorability of certain words was linked to the frequency with which the brain used them as semantic links between other memories, making them often-visited hubs in individuals's memory networks, and therefore places the brain jumped to early and often when retrieving memories. This idea was supported by observed activity in participants' anterior temporal lobe, a language center.

In epilepsy patients, these words were so frequently recalled that subjects often shouted them out even when they were incorrect responses to word-pair inquiries.

Seek, find

Modern search engines no longer simply look for raw words when resolving an inquiry: They also look for semantic — contextual and meaning — connections so that the results they present may better anticipate what it is you're looking for. Xie suggests something similar may be happening in the brain: "You know when you type words into a search engine, and it shows you a list of highly relevant guesses? It feels like the search engine is reading your mind. Well, our results suggest that the brains of the subjects in this study did something similar when they tried to recall a paired word, and we think that this may happen when we remember many of our past experiences."

He also notes that it may one day be possible to leverage individuals' apparently wired-in knowledge of their language as a fixed point against which to assess the health of their memory and brain.

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