\n<\/p>\n
The big bang wasn\u2019t a bang in the traditional sense\u2014but it was nonetheless the start of important things: for one, space; another, time. Thirdly, it began the conditions and processes that eventually resulted in us humans, who can sit here and wonder about space and time. The big bang was, effectively, the beginning of the universe. According to the logic of human brains, it seems like there must have been something before the big bang, even if \u201cbefore\u201d is the wrong word because there was no time until after.<\/p>\n
The good news for us is that physicists do have ways of thinking about\u2014and even empirically studying\u2014the origins of the origin of the universe. Counterintuitive and impossible as it may seem, cosmologists are even making progress in determining which wild ideas might peel back the veil on that early era, even though it remains inaccessible to telescopes.<\/p>\n
For millennia, what happened before and at the beginning of the universe was not a question scientists could even scratch at. Cosmological queries were the dominion of philosophers, says Jenann Ismael\u2014herself a philosopher of physics at Johns Hopkins University. The most fundamental query, of course, is where we come from\u2014a question as popular among philosophers as it is with the rest of us. Other questions, Ismael says, include doozies such as \u201cWhat are space and time? Does time have a beginning? Does space have boundaries?\u201d<\/p>\n
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Even after cosmology became a hard science, the field was a bit sketchy, Ismael says. \u201cThe science was one-and-a-half facts,\u201d she adds. The sentiment, she says, is usually attributed to physicist James Jeans. But that has changed in the past century or so as the philosophers\u2019 musings have wandered into the realm of theory, experiment and data. \u201cThese old conceptual questions are arising in ways that have new angles, a new spin and a new framework,\u201d Ismael continues.<\/p>\n
It\u2019s unclear whether science as a discipline\u2014and scientists as people\u2014will ever be able to answer some questions definitively. After all, no one can \u201csee\u201d before the big bang, and no one will ever be able to\u2014at least not directly. But the current and future universe, researchers are learning, may contain clues about the distant past.<\/p>\n
And as scientists push the boundaries of what can be known, they are testing their theories about the before before\u2014the only way to get closer to potential truth. \u201cI\u2019m happy to listen to any framework, but I only start taking it seriously when it produces a clean observational target that a real instrument can go after,\u201d says Brian Keating, a cosmologist at the University of California, San Diego. \u201cIf there isn\u2019t a discriminant you can measure, you\u2019re doing metaphysics with equations.\u201d<\/p>\n
Here are three ideas that he and other scientists take seriously about the cosmos\u2019s ultimate origins.<\/p>\n
Quantum mechanics is the physics of the extremely small, ruled by statistics and uncertainty. It\u2019s also what may have shaped the early universe. To understand the quantum cosmos, scientists calculate the probability of a given output from a certain input.<\/p>\n
In cosmology, the \u201coutput\u201d is the universe as it looks today. \u201cThe question is: What should the input be?\u201d says Jean-Luc Lehners, former head of the Theoretical Cosmology group at the Max Planck Institute for Gravitational Physics (Albert Einstein Institute) in Germany.<\/p>\n
Physicists can break up the problem into chunks of outputs and inputs. If they consider the modern universe to be the output, they can try to figure out what input might have produced it. Then they can step backward by taking that input as a new output and determine what conditions earlier in the universe might have produced that state, and so on. They can theoretically (if they have a lot of time on their hands) do that forever, going in steps to reach the before before\u2014and even before that.<\/p>\n
That infinite regression, however, didn\u2019t make sense to physicists Stephen Hawking and James Hartle, who worked on the question together in the 1980s. They decided to eliminate the universe\u2019s ultimate input\u2014its \u201cbeginning.\u201d Instead they formed a model of the universe called the no-boundary proposal. They suggested time and space form a closed, rounded surface: a four-dimensional hemisphere of spacetime.<\/p>\n
Does that not make sense? Try this: imagine the universe like the globe of Earth. The big bang is the North Pole. There is no \u201cbefore\u201d it, just as there is no north of north. Before becomes irrelevant as a concept. \u201cIt\u2019s almost like a Zen idea,\u201d Lehners says. And it\u2019s one he\u2019s toying with in calculations to see if he can re-create the universe we see today from a round place with no north of north.<\/p>\n
\u201cThe no-boundary proposal has a decent amount of support, or at least interest, within the physics community,\u201d says Sean Carroll, a professor of natural philosophy at Johns Hopkins University. He notes that some scientists worry about how well-defined the idea is, but he finds it to be a \u201cnatural starting point,\u201d given what we know about quantum gravity.<\/p>\n
Paul Steinhardt, a physicist at Princeton University, has another idea about what happened before the universe as we know it began. It stands in opposition to an idea that he helped shape: this concept suggests that, after the big bang, spacetime expanded very quickly for a very short period of time called inflation. The inflation scenario is meant to explain why the universe looks flat and similar in every place our telescopes can look.<\/p>\n
After helping to establish inflation theory, however, Steinhardt started doubt the idea\u2014in part because it has required constant tweaking to keep it consistent with our measurements of the cosmos. \u201cIt\u2019s really hard to think of a historical example where that actually led to what turns out to be the right answer,\u201d Steinhardt says. \u201cAlmost always, that’s a sign that the Titanic is sinking.\u201d<\/p>\n
Time to get in a lifeboat, he thought. So he came up with a cyclic universe: one that balloons significantly in size, as ours seems to be doing now, then shrinks a little and then starts expanding all over again. \u201cWhen people think about contracting universes, they’re usually thinking about things coming to a crunch,\u201d Steinhardt says\u2014the cosmos collapsing back down into an infinitesimally small point. That\u2019s not what Steinhardt is talking about: he thinks the universe perhaps contracts slowly\u2014to a smaller fraction of its size but not to nothing. That shrinking smooths things out in ways inflation fails to explain, he says, while still producing a cosmos that appears flat and the same in all directions.<\/p>\n
Steinhardt adds that what looks like a big bang is actually not: the universe expands, then slowly contracts and then quickly goes back to expanding. The fast transition between contraction and expansion is not a bang but a \u201cbig bounce.\u201d<\/p>\n
Steinhardt hopes to test this idea not just by examining the past but also by taking data from the present and watching the future carefully. \u201cIt makes an obvious prediction, which is that the current phase of accelerated expansion can\u2019t continue forever,\u201d Steinhardt says. \u201cIt must end.\u201d This idea, in turn, raises a new question: \u201cCould it already be in the process of ending now?\u201d he asks.<\/p>\n
Our measurements about how the universe is expanding come from relatively faraway objects that emitted their light a long time ago. Things could have changed, and we might not know yet because the effects would be hard to measure. \u201cWe\u2019d have to look at objects very close by in order to detect it,\u201d Steinhardt says. That\u2019s not cosmologists\u2019 forte, and they would have to develop new techniques and instruments to look nearby for such effects.<\/p>\n
Even more intriguingly, Steinhardt says that because \u201cnothing bad happens to space\u201d during the contraction and bounce, information\u2014even objects such as black holes\u2014can pass from before the bounce to after. \u201cThere might be things in our observable universe which are from before,\u201d he says. Keep an eye out.<\/p>\n
Another big idea about the before before is of interest to Latham Boyle, a researcher at the Higgs Center for Theoretical Physics at the University of Edinburgh, who was formerly Steinhardt\u2019s graduate student. Like the big bounce concept, Boyle\u2019s favored proposal is pretty simple conceptually\u2014and it similarly eschews inflation. \u201cThere\u2019s the universe after the big bang and the universe before the big bang,\u201d he says, \u201cand they\u2019re kind of mirror copies of one another.\u201d<\/p>\n
Picture this, Boyle says, like the points of two ice cream cones touching each other, with their contact representing the big bang. \u201cTime marches away from the big bang in both directions,\u201d he says. On our side, it goes forward; on the mirror side, it goes backward. What happened before the big bang is the reflected opposite of what happened after. And that doesn\u2019t just include time: here, there is matter; there, there is antimatter. Here, left is left; there, left is right.<\/p>\n
Boyle has ideas for observations that could support (or nullify) his theory, which is called the CPT-symmetric (charge-parity-time-symmetric) universe. For one, a CPT-symmetric universe wouldn\u2019t have sent gravitational waves shimmering through space from the beginning of the universe, as classical cosmology theories predict. Astronomers have been hunting for such signals. If these waves are eventually detected, that would rule this idea out.<\/p>\n
Boyle\u2019s hypothesis also predicts that dark matter could be explained by a particular kind of neutrino. He hopes cosmological instruments will reveal more information about neutrinos soon. The model\u2019s connection to particle physics, among other aspects, makes this idea intriguing, Carroll says.<\/p>\n
\u201cWhat I like here is the economy,\u201d Keating says, \u201cand the fact that it sticks its neck out,\u201d focusing on the kinds of specific, physical predictions experimentalists like him need.<\/p>\n
Each of these scientists is attached to their own idea. But Lehners, interviewed late last year, isn\u2019t confident any of them will stand the test of time\u2014whatever time is. \u201cI think it\u2019s completely preposterous that, in the year 2025, we should understand the beginning of the universe,\u201d he says. \u201cWhy not in the year 2,000,025 or whatever?\u201d<\/p>\n
And even if researchers think they are getting close, they could be approaching a false summit: that frustrating place that looks, when you\u2019re hiking, like the top of the mountain but is actually a mere bump blocking your view of the true peak\u2014or your view of what you think is the true peak but is, in fact, just another bump. \u201cIn general, I think that it\u2019s extremely plausible that there was something before the big bang,\u201d Carroll says, \u201cbut it’s also very plausible that the big bang was truly the beginning. There\u2019s too much we’re just unsure about, and I am a bit skeptical that the state of the art is good enough to allow us to draw any firm experimental or observational conclusions out of any of these models.\u201d<\/p>\n
But cosmologists aren\u2019t studying the ultimate origins because they think the mystery will be resolved in their lifetime. Lehner imagines himself as part of an intergenerational project helping humanity trek closer and closer to a truth we may never find.<\/p>\n
Studying such a physically and philosophically inaccessible topic is fundamentally different from other types of science\u2014those quests at least exist in our plane of space and time. It almost seems like the question isn\u2019t actually within the realm of science. But science often involves probing things we cannot access, at least at the start, philosopher of physics Ismael says. Scientists predicted atoms before we could see them, and black holes and dark matter still lie beyond our ability to detect directly\u2014yet investigating them is clearly scientific. \u201cI think the benchmark for what counts as science has moved,\u201d she says. And it will continue to\u2014including, perhaps, backward to the before that may not be a before.<\/p>\n","protected":false},"excerpt":{"rendered":"
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