What happened before the Big Bang?
[거사 주]:
"Big Bang" 가설이 전에 말씀드렸대로 100년이 지나면서 그 의미가 탈색되는 거 같습니다.
영국의 물리학자 Roger Penrose나 Stephen Hawking 이 주장한 "Singuilarity"에 의한 가설은 석연치 않은 면이 많았습니다. 수학적인 논리를 전개하기 위해서 설정한 "시간/우주의 시작"이라고 하면, 당연히 그전엔 어찌 되었는가?를 생각할 수밖에 없죠. 이제 학계에서는 여러 학설이 대두되었지만, "Big Bounce"이라는 가설이 가장 설득력이 있다는군요. 이 가설은 언제부터 반복되는 과정인지는 모르지만, 매 1 Trillion(1조, 10^12)년마다 반복이 된다고 합니다만, 그 주기가 너무 황당합니다. 현 우주의 나이가 13.8 Billion(138억, 13.8 x 10^9)년이라는데, 마지막 6단계에 이르고 있으면 "Big Crunch"가 시작되고 또 "Big Boune"가 반복된다는 얘깁니다. 그리고 이제 "Singularity" 개념 대신에, "Quantum Fluctuations"을 통해서 "Big Bounce"가 일어난다고 하는 가설인데, 아직도 해명이 거의 불가한 영역이라 황당하기 그지없습니다.
I. Has our universe cycled through numerous "big crunches" and "big bounces?"
By Paul Sutter published February 11, 2022
Paul M. Sutter is an astrophysicist at SUNY Stony Brook and the Flatiron Institute in New York City. Paul received his PhD in Physics from the University of Illinois at Urbana-Champaign in 2011, and spent three years at the Paris Institute of Astrophysics, followed by a research fellowship in Trieste, Italy, His research focuses on many diverse topics, from the emptiest regions of the universe to the earliest moments of the Big Bang to the hunt for the first stars. As an "Agent to the Stars, " Paul has passionately engaged the public in science outreach for several years. He is the host of the popular "Ask a Spaceman!" podcast, author of "Your Place in the Universe" and "How to Die in Space" and he frequently appears on TV — including on The Weather Channel, for which he serves as Official Space Specialist.
In the beginning, there was an infinitely dense, tiny ball of matter. Then, it all went bang, giving rise to the atoms, molecules, stars and galaxies we see today. Or at least, that's what we've been told by physicists for the past several decades. But new theoretical physics research has recently revealed a possible window into the very early universe, showing that it may not be "very early" after all. Instead it may be just the latest iteration of a bang-bounce cycle that has been going on for … well, at least once, and possibly forever.
Even earlier, this thinking goes, at some point our entire universe — all the stars, all the galaxies, all the everything — was the size of a peach and had a temperature of over a quadrillion degrees.
Amazingly, this fantastical story holds up to all current observations. Astronomers have done everything from observing the leftover electromagnetic radiation from the young universe to measuring the abundance of the lightest elements and found that they all line up with what the Big Bang predicts. As far as we can tell, this is an accurate portrait of our early universe.
But as good as it is, we know that the Big Bang picture is not complete — there's a puzzle piece missing, and that piece is the earliest moments of the universe itself. That's a pretty big piece.
The problem is that the physics that we use to understand the early universe (a wonderfully complicated mishmash of general relativity and high-energy particle physics) can take us only so far before breaking down. As we try to push deeper and deeper into the first moments of our cosmos, the math gets harder and harder to solve, all the way to the point where it just … quits
The main sign that we have terrain yet to be explored is the presence of a "singularity" or a point of infinite density, at the beginning of the Big Bang. Taken at face value, this tells us that at one point, the universe was crammed into an infinitely tiny, infinitely dense point. This is obviously absurd, and what it really tells us is that we need new physics to solve this problem — our current toolkit just isn't good enough.
To save the day, we need some new physics — something that is capable of handling gravity and the other forces, combined, at ultrahigh energies. And that's exactly what string theory claims to be: a model of physics that is capable of handling gravity and the other forces, combined, at ultrahigh energies. Which means that string theory claims it can explain the earliest moments of the universe.
One of the earliest string theory notions is the "ekpyrotic" universe, which comes from the Greek word for "conflagration," or fire. In this scenario, what we know as the Big Bang was sparked by something else happening before it — the Big Bang was not a beginning, but one part of a larger process.
As cool as this sounds, early versions of the cyclic model had difficulty matching observations — which is a major deal when you're trying to do science and not just telling stories around the campfire.
The main hurdle was agreeing with our observations of the cosmic microwave background, the fossil light leftover from when the universe was only 380,000 years old. While we can't see directly past that wall of light, if you start theoretically tinkering with the physics of the infant cosmos, you affect that afterglow light pattern.
And so, it seemed that a cyclic universe was a neat but incorrect idea.
But the ekpyrotic torch has been kept lit over the years, and a paper published in March 2020 has explored the wrinkles in the mathematics and uncovered some previously missed opportunities. The two physicists who authored the study, Robert Brandenberger and Ziwei Wang, both of McGill University in Canada, found that in the moment of the "bounce," when our universe shrinks to an incredibly small point and returns to a Big Bang state, it's possible to line everything up to get the proper observationally tested result. In other words, the complicated (and, admittedly, poorly understood) physics of this critical epoch may indeed allow for a radically revised view of our time and place in the cosmos. But to fully test this model, we'll have to wait for a new generation of cosmology experiments. So let's wait to break out the ekpyrotic champagne.
II. What Existed Before the Big Bang?
By: Robert Lamb & Patrick J. Kiger | Updated: Apr 15, 2021
It is difficult enough to imagine a time, roughly 13.7 billion years ago, when the entire universe existed as a singularity. According to the Big Bang theory, one of the main contenders vying to explain how the universe came to be, all the matter in the cosmos -- all of space itself -- existed in a form smaller than a subatomic particle [source: Wall].
Once you think about that, an even more difficult question arises: What existed just before the big bang occurred?The question itself predates modern cosmology by at least 1,600 years. Fourth-century theologian St. Augustine wrestled with question of what existed before God created the universe. His conclusion was that the Biblical phrase "In the beginning" implied that God had made nothing previously. Moreover, he argued that the world was not made by God at a certain time, but that time and the universe had been created simultaneously. [source: Villanova University]
In the early 20th century, Albert Einstein came to very similar conclusions with his theory of general relativity. Just consider the effect of mass on time. A planet's hefty mass warps time -- making time run a tiny bit slower for a human on Earth's surface than a satellite in orbit. The difference is too small to notice, but time even runs more slowly for someone standing next to a large boulder than it does for a person standing alone in a field. [source: Redd].
Based upon Einstein's work, Belgian cosmologist Rev. Georges Lemaître published a paper in 1927 that proposed the universe started out as a singularity and that the Big Bang led to its expansion [source: Soter and Tyson].
According to Einstein's theory of relativity, time only came into being as that primordial singularity expanded toward its current size and shape.
Case closed? Far from it. This is one cosmological quandary that won't stay dead. In the decades following Einstein's death, the advent of quantum physics and a host of new theories resurrected questions about the pre-big bang universe. Keep reading to learn about some of them.
Did Our Universe Bubble Out of a Previous One?
This illustration shows the cosmic microwave background — radiation left over from the Big Bang — gathered by the Planck orbital observatory. ESA AND THE PLANCK COLLABORATION
Here's a thought: What if our universe is but the offspring of another, older universe? Some astrophysicists speculate that this story is written in the relic radiation left over from the Big Bang: the cosmic microwave background (CMB).
Astronomers first observed the CMB in 1965, and it quickly created problems for the Big Bang theory -- problems that were subsequently addressed (for a while) in 1981 with the inflation theory. This theory entails an extremely rapid expansion of the universe in the first few moments of its existence. It also accounts for temperature and density fluctuations in the CMB, but dictates that those fluctuations should be uniform.
That's not the case. Recent mapping efforts actually suggest that the universe is lopsided, with more fluctuations in some areas than in others. Some cosmologists see this observation as supporting evidence that our universe "bubbled off" from a parent universe, in the words of California Institute of Technology researcher Adrienne Erickcek [source: Lintott]
In chaotic inflation theory, this concept goes even deeper: an endless progression of inflationary bubbles, each becoming a universe, and each of these birthing even more inflationary bubbles in an immeasurable multiverse [source: Jones].
Still other models revolve around the formation of the pre-Big Bang singularity itself. If you think of black holes as cosmic trash compactors, they stand as prime candidates for all that primordial compression, so our expanding universe could theoretically be the white hole output from a black hole in another universe. A white hole is a hypothetical body that acts in the opposite manner of a black hole, giving off serious energy and matter rather than sucking it in. Think of it as a cosmic exhaust valve. Some scientists propose that our universe may have been born inside a black hole, and every black hole in our own universe could each contain separate universes as well [source: Choi].
But some scientists think the universe started, not with a Big Bang, but with a Big Bounce.
The Big Bounce
Long ago, medieval religious philosophers in India taught that the universe goes through an endless cycle of creation and destruction, in which it evolves from an undifferentiated mass unto the complex reality the we see around us, before destroying itself and starting anew [source: Davis].
Some contemporary scientists have arrived at an idea with striking parallels. They believe that instead of a Big Bang, the universe expands and contracts in a cycle, bouncing back each time that it shrinks to a certain size. In the Big Bounce theory, each cycle would begin with a small, smooth universe that wouldn't be as tiny as the singularity. It would gradually expand, and become clumpier and more warped over time. Eventually, it would reach a point where it would start to collapse and gradually smooth itself out, as it shrank to the size of the starting point. Then, the cycle would begin anew [source: Wolchover].
For the Big Bounce idea to work, it has to find a way around the singularity theorems developed by British physicists Roger Penrose and Stephen Hawking, which suggest that a contracting universe would shrink all the way down to a singularity, in the fashion that a massive dying star eventually condenses to form a black hole. To do that, Big Bounce models depend upon the idea of negative energy counteracting gravity and reversing the collapse, so that that the universe and time-space would be driven apart again and again [source: Wolchover].
These cycles of contraction and expansion would repeat themselves, about once every trillion years [source: Taylor]. The Big Bounce would make a departure from western civilization's view of reality since St. Augustine, because it would recognize that time actually existed before the universe as we know it.
But whether it as a Big Bang or a Big Bounce, the question of what existed before our present universe remains an open question. Perhaps nothing. Perhaps another universe or a different version of our own. Perhaps a sea of universes, each with a different set of laws dictating its physical reality.(-)
Originally Published: Jan 7, 2019
'이야기 마당 > 과학 이야기' 카테고리의 다른 글
| 우리는 여기까지만 알면 됩니다- 팽창속도 추가 (0) | 2022.04.10 |
|---|---|
| 생명체가 존재할 가능성이 있는 행성들을 찾았다는데--- (0) | 2022.04.02 |
| "Big Bang" 이 더 이상 우주의 시작이 아니다 (2) | 2022.03.16 |
| Where are we relative to the Big Bang? (0) | 2022.03.10 |
| 우주 끝까지 절대로 갈 수도 볼 수도 없다 (0) | 2022.01.05 |