The Big Bang was no bang in the traditional sense – but it was nevertheless the beginning of important things: for one, space; another time. Third, it initiated the conditions and processes that ultimately resulted in the formation of 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 the human mind, it seems that there must have been something before the Big Bang, even if “before” is the wrong word because there was no time until then.
The good news for us is that physicists have ways to think about, and even empirically study, the origin of the universe. Paradoxical and impossible as it may seem, cosmologists are also making progress in determining what wild ideas might uncover that early era, even if it remains inaccessible to telescopes.
For millennia, what happened before and at the beginning of the universe was not a question that scientists could even scratch. Zenain Ismail, a philosopher of physics at Johns Hopkins University, says that cosmological questions were the prerogative of philosophers. Of course, the most fundamental question is where we came from – a question as popular among philosophers as it is among the rest of us. Ismail says other questions include “What are space and time? Does time have a beginning? Does space have boundaries?” Questions like.
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Ismail says that even after cosmology became a hard science, the field was still a bit obscure. She adds, “Science was based on one and a half facts.” This sentiment, she says, is usually attributed to physicist James Jeans. But this has changed over the past century as philosophers’ thinking has strayed into the realms of theory, experiment, and data. Ismail adds, “These old ideological questions are being raised in ways that have new angles, new spins and new framing.”
It is not clear that science as a discipline—and scientists as people—will ever be able to answer certain questions definitively. After all, no one can “see” before the Big Bang, and no one ever will—at least not directly. But researchers are discovering that the present and future universe may hold clues about the distant past.
And as scientists push the boundaries of what can be known, they are testing their theories about the first ever before – potentially the only way to get closer to the truth. Brian Keating, a cosmologist at the University of California, San Diego, says, “I’m happy to hear any framework, but I only start taking it seriously when it produces a clean observational target that a real instrument can pursue.” “If there is no differential that you can measure, you are doing metaphysics with equations.”
Here are three ideas that he and other scientists take seriously about the ultimate origin of the universe.
no-boundary proposal
Quantum mechanics is tiny physics governed by statistics and uncertainty. It may also have shaped the early universe. To understand the quantum universe, scientists calculate the probability of a given output from a certain input.
In cosmology, the “output” is the universe as it appears today. “The question is: what should the input be?” says Jean-Luc Lehners, former head of the theoretical cosmology group at the Max Planck Institute for Gravitational Physics (Albert Einstein Institute) in Germany.
Physicists can break the problem down into output and input pieces. If they consider the modern universe to be the output, they can try to figure out what inputs might have generated it. They can then go back, taking that input as a new output and determining what conditions might have arisen in the universe in the first place He State, etc. They could theoretically (if they had a lot of time) do this forever, taking steps to get to the first – and even earlier.
However, that infinite regress made no sense to physicists Stephen Hawking and James Hartle, who worked together on this question in the 1980s. He decided to eliminate the last input to the universe – its “beginning”. Instead he created a model of the universe called the no-boundary proposal. He suggested that time and space form a closed, spherical surface: a four-dimensional hemisphere of space-time.
Does this make no sense? Try this: Imagine the universe as the Earth’s globe. The Big Bang is the North Pole. There is no one before it, just as there is no answer to the answer. The first becomes irrelevant as a concept. “It’s almost like a Zen idea,” Lehners says. And this is the calculation he is working with to see if he can recreate the universe we see today from a round place, to which there is no answer.
“The no-boundary proposal has a substantial amount of support or at least interest within the physics community,” says Shawn Carroll, professor of natural philosophy at Johns Hopkins University. He notes that some scientists are concerned about how well defined the idea is, but given what we know about quantum gravity, he considers it a “natural starting point.”
A bouncing, cyclical universe
Princeton University physicist Paul Steinhardt has another idea about what happened before the universe as we know it began. This stands in opposition to the idea he helped shape: this concept suggests that, after the big bang, space-time expanded very rapidly for a very short period of time in a process called inflation. The inflationary scenario purports to explain why the universe appears flat and the same everywhere our telescopes can see.
However, after helping to establish inflationary theory, Steinhardt began to doubt the idea – partly because it requires constant change to keep it consistent with our measurements of the universe. “It’s really hard to think of a historical example where we actually got the right answer,” says Steinhardt. “Almost always, this is a sign that titanic Drowning.”
He thought, time has come to get into the lifeboat. So he came up with a cyclical universe: one that grows quite large in size, as ours is happening now, then shrinks a bit and starts expanding again. “When people think about the contraction of the universe, they’re usually thinking about things coming to a crisis,” says Steinhardt — the universe collapsing back into an extremely small point. That’s not what Steinhardt is talking about: He believes the universe is probably shrinking slowly – to a small fraction of its size, but not to zero. He says that shrinking smoothes things out in ways that inflation fails to explain, while still producing a universe that appears flat and the same in all directions.
steinhardt says what looks like It’s not really like the Big Bang: The universe expands, then slowly contracts, and then rapidly returns to expansion. The sharp transition between contraction and expansion is not a bang but a “big boom”.
Steinhardt hopes to test this idea not only by examining the past but also by taking data from the present and looking carefully into the future. “This makes a clear prediction, which is that the current phase of accelerated expansion cannot continue forever,” says Steinhardt. “This must end.” This idea, in turn, raises a new question: “Is it already in the process of being eliminated?” he asks.
Our measurements of how the universe is expanding come from relatively distant objects that emitted their light a long time ago. Things could have changed, and we might not know yet because the effects would be difficult to measure. “We have to look at objects very closely to detect it,” says Steinhardt. This is not the specialty of cosmologists, and they must develop new techniques and instruments to observe such effects up close.
Even more interestingly, Steinhardt says that because “nothing bad happens to space” during the contraction and bounce, information – even about objects like black holes – can be passed from before to after the bounce. “There may be things in our observable universe that already are,” he says. Keep an eye out.
mirror universe
Another big idea about the first is of interest to Latham Boyle, a researcher at the Higgs Center for Theoretical Physics at the University of Edinburgh, who was previously Steinhardt’s graduate student. Like the big boom hypothesis, Boyle’s preferred proposal is conceptually very simple – and it also avoids inflation. “There is a universe after the Big Bang and a universe before the Big Bang,” he says, “and they are mirror copies of each other.”
Imagine it, says Boyle, as if the points of two ice cream cones were touching each other, and their contact represented the big bang. “Time goes away in both directions with a big bang,” he says. It moves forward from us; Towards the mirror, it moves backwards. What happened before the Big Bang is reflected in the opposite of what happened after. And this does not involve only time: here, there is matter; There is antimatter. Here left is left; There, left is right.
Boyle has ideas for observations that could support (or refute) his theory, called a CPT-symmetric (charge-parity-time-symmetric) universe. For one, a CPT-symmetric universe would not have sent gravitational waves flaring through space from the beginning of the universe, as classical cosmological theories predict. Astronomers are looking for such signs. If these waves are eventually detected, it would rule out this idea.
Boyle’s hypothesis also predicts that dark matter can be explained by a special type of neutrino. He hopes that cosmological instruments will soon reveal more information about neutrinos. Carroll says the model’s connection to particle physics, among other aspects, makes the idea interesting.
“What I like here is the economy,” says Keating, “and the fact that it sticks its neck out, focusing on the kind of specific, physical predictions that experimentalists like him need.”
test of time
Each of these scientists is attached to his own idea. But the Lehners, interviewed late last year, don’t believe any of them will stand the test of time – whatever the timing may be. He says, “I think it’s completely absurd that, in the year 2025, we should understand the beginning of the universe.” “Why not in the year 2,000,025 or whatever?”
And even if researchers think they’re getting closer, they may be approaching a false summit: that dismal place that, when you’re hiking, looks like a mountain peak, but is actually a mere bump blocking your view of the real peak – or what you think is the true peak but, in reality, is just another bump. Carroll says, “In general, I think it’s extremely plausible that there was something before the Big Bang, but it’s also very plausible that the Big Bang was actually the beginning. There’s a lot about which we’re unsure, and I have little doubt that the state of the art is good enough to allow us to draw any solid experimental or observational conclusions from any of these models.”
But cosmologists are not studying the ultimate origin because they think the mystery will be solved in their lifetime. Lehner imagines himself as part of an intergenerational project that helps humanity move closer and closer to the truth we may never find.
The study of such a physically and philosophically inaccessible subject is fundamentally different from other types of science – those discoveries exist at least at our level of space and time. It almost seems that the question is not really within the scope of science. But physics philosopher Ismail says that science often involves investigating things we can’t reach, at least initially. Scientists predicted atoms long before we could see them, and black holes and dark matter are still beyond our ability to detect directly – yet it is clearly scientific to investigate them. “I think science has changed the benchmark for what matters,” she says, “and that will continue to happen—including, perhaps, going back to what may not have happened before.”
