![According to a new theory, the Big Bang, shown here in an artist's concept, may not have been the beginning of everything. [Credit: Stephen van Vuuren]](http://scienceline.org/_s/files/2008/02/bigbang1.jpg)
** Editor’s Note: The staff of Scienceline is taking a short break to work on future stories. This article originally appeared February 27, 2008.**
For decades, the Big Bang has been taught in high school physics classes as the leading theory for the way the universe began. But despite the overwhelming evidence supporting it, several questions linger for physicists. How could something come from nothing? And why do the laws of physics not hold up at the bang?
Now, some scientists say that the Big Bang was not the beginning, and that there was a universe before ours. The key is a new concept of gravity, which explains how such a universe could exist without violating the laws of physics.
If correct, Martin Bojowald, main architect of the theory and Penn State physicist, will have overcome the inability to explain the early universe. This problem has left scientists, including the likes of Einstein, perplexed for years.
“In my opinion, this is the single most embarrassing problem of physics,” said Max Tegmark, an astrophysicist at Massachusetts Institute of Technology.
In simple terms, Bojowald’s theory, published in August’s Nature Physics, can be described as a Big Crunch followed by a Big Bounce. He suggests there was a universe before ours that was collapsing and getting hotter (the crunch). Then, when it reached a maximum density and temperature, it was driven apart (the bounce), forming our current universe.
The main ingredient of Bojowald’s crunch-bounce theory is loop quantum gravity, a new concept that combines the traditional understanding of gravity with the quantum effect, which says that matter behaves differently at the subatomic level. Many scientists believe it is the absence of the quantum effect in equations that describe the Big Bang that lead to impossible phenomena like infinite temperature and density.
In Bojowald’s model, without the quantum effect, there would be no force to drive it apart; the collapsing universe that preceded ours would simply collapse into oblivion. But with the quantum effect, reaching a certain temperature and density threshold would trigger repulsive forces to drive the universe apart.
“The repulsive forces would stop the complete collapse and also turn it around into an expansion,” Bojowald said, effectively preventing temperature and density from approaching infinity.
While the crunch-bounce solves this problem of infinite temperature and density, the challenge becomes finding evidence to support the existence of the previous universe. To see if there was anything before the bounce, you would have to observe the distribution of particles small enough to have passed through the very dense early universe. Currently, neutrinos, very tiny particles that travel close to the speed of light, fit the bill. But they are very hard to detect.
If the method of detecting neutrinos improves, they could point to a previous universe. However, Bojowald said that in order to do this he first needs to answer the following question: If there was a universe before the bounce, what would the distribution of neutrinos look like today? Then, using equations and computer simulations he could make predictions and compare those with actual observations of neutrinos.
Other scientists find the crunch-bounce theory intriguing, but point out that there are still problems. Sean Carroll, a physicist from the California Institute of Technology, said his main concern is that the model overlooks the idea of entropy.
One way that entropy can be defined is the tendency for particles, energy or heat to disperse rather than remain clumped together. For example, smoke leaving a chimney will spread out, rather than stay in one place, thus increasing in entropy.
The expanding universe also acts in this manner and is continually increasing in entropy. An unusual observation, according to Carroll, is the universe’s low entropy near the Big Bang. Since this is such an unusual phenomenon, he said it was necessary for any new theory to explain why entropy is so low at that point.
“It would be like walking into a room and finding all the air molecules on one side,” Carroll said.
Aside from the crunch-bounce theory, other credible challenges to the Big Bang are emerging, too. Cambridge’s Neil Turok and Princeton’s Paul Steinhardt have a model they call the Cyclic Universe. These physicists believe that the Big Bang was not a unique event, but one in a series of bangs with more bangs yet to come.
Bojowald’s theory does not discount this idea of “multiverses.” And neither theory estimates the number of previous universes or when the next crunch will happen. Turok and Steinhardt’s theory differs from Bojowald’s mainly in the mathematics they use to describe it.
They explain their model using string theory, a branch of physics that views matter as one-dimensional “strings.” Using the equations of string theory, they come up with a different picture of the early universe.
Like Bojowald, they were driven by the belief that the current Big Bang model leaves too many unanswered questions. Steinhardt said that the more scientists understand about the universe, the more the current model does not work. “Maybe we’re on the wrong track,” he said.
So far, though, none of the new models have overturned the Big Bang to emerge as the leading alternative, primarily because proving the existence of a previous universe is so difficult. Steinhardt says much more data and evidence are necessary before a paradigm shift can occur. “Most of us will stick to something until forced to give it up,” he said.
But even if these new ideas about the origin of the known universe are correct, they cannot address the ultimate questions: What came before all of those previous universes and Big Bangs? When did it all begin?
“We’re not going to actually answer the question of where the beginning was,” Bojowald said. “We’re just pushing the beginning back in time.”
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February 28th, 2008 at 11:42 am
This is not new.
March 11th, 2008 at 2:30 pm
Are we, then, edging back towards the universe having always existed, if we consider whatever there was before BB as being part of the universe? This seems as improbable as does the idea that the universe created itself from the absolute nothing. In an eternally existing universe, I can´t see how you can have events, like me typing on my computer at this moment (in my time). Any event would surely have occurred an eternity ago in an eternal universe and hence would not have occurred at all. The only eternal universe I can imagine would be one with nothing but totally empty space, where no events ever can or do occur and also without “quantum fluctuations”.
March 25th, 2008 at 11:58 pm
maybe in 10,000 years we might begin to have the intelligence to start to understand where it all came from. the only thing wrong with all the theories floating around is that we have the audacity to think with our limited intelligence we could begin to understand any of it. when is science going to wake up and realize we are still in single cell state. We marvel at all the things we have done and we are still that 3 feet high half monkey running from the lions trying to keep from being eaten of killed by the nearest clan. People string words together like they know what they are talking about and they know nothing.
April 10th, 2008 at 7:31 pm
1. This theory doesn’t really answer any questions, it merely moves them back in time. Instead of asking where our universe came from, we now ask where the previous universe came from.
2. I thought this theory had already been thrown out. Years ago, we had the oscillating universe theory. For that to be a valid theory, the universe would have to be expanding at a decreasing rate, which is the opposite of what we see.
If there had been a previous universe, its total energy content would have to be the same as ours (conservation of energy/mass). If it didn’t have the energy to infintely expand, then our universe wouldn’t either. If it did have the energy to infinitely expand, then our universe would never have been born. Again, this is the opposite of our astronomical observations. On this basis alone, I think the theory described is invalid.
Just the ramblings of a dumb ole’ engineer.
April 11th, 2008 at 7:14 am
Cosmological observations provide an incredibly rich set of clues to the pre-big bang universe. Do you see any flaws in: The pre-big bank universe at BigCrash.org?
…
In the beginning (in the pre-big bang universe) there was only the vast vacuum of space and time. But this vacuum was not sterile, it was seething with vacuum energy. This vacuum energy field permeates and defines the universe, an astronomically large sphere of energy. And just as matter generates gravity by warping space and time, so does energy and this is the force that defines the size and shape of the universe, and also the force that bestows mass on matter…
…When a virtual matter/anti-matter pair becomes a matter matter pair, the virtual particles are no longer able to mutually annihilate and they become real, stealing energy from the vacuum energy of space. This is the mechanism of slow matter creation in the first phase of the pre-big bang universe. Over perhaps a billion billion years, clouds of matter form over the entire universe, and eventually coalesce into cosmological bodies and eventually the first pre-big bang black hole, which starts the second phase of the pre-big bang universe, fast accretion of matter from vacuum energy by black holes…
April 14th, 2008 at 5:28 pm
JTankers:
“Cosmological observations provide an incredibly rich set of clues to the pre-big bang universe. Do you see any flaws in: The pre-big bank universe at BigCrash.org?”
I really don´t know where you get this from, as there is no evidence at all about a pre-BB universe, let alone “incredibly rich set of clues”.
This is from Stephen Hawking´s “A Briefer History of Time”:
“Correspondingly, if, as is the case, we know only what has happened since the big bang, we cannot determine what happened beforehand. As far as we are concerned, events before the big bang can have no consequences and so should not form part of a scientific model of the universe. We should therefore cut them out of the model and say that the big bang was the beginning of time. This means that questions such as who set up the conditions for the big bang are not questions that science addresses.” I don´t see much hint of him knowing anything about the rich clues about any pre-BB there might have been. However…I don´t really understand why events before a big bang can have no consequences, particularly as they were probably responsible for the BB in the first place. I also note that BB itself is coming under increasing attack.
I find it hard to accept that the whole universe could have been concentrated at a point at infinite density. What is “infinite density”?
Also, what caused BB? A cosmologist that I asked said that it happened for no cause, but I don´t believe that a status quo can be interrupted for no cause. Maybe we don´t or cannot know the cause, but I´ll bet there was one. (In a subsequent email he asked me how you go south when you get to the south pole. I´m still trying to work out what he is saying.)
June 23rd, 2008 at 1:05 pm
Obviously ,science can only prove a theory from what it can observe or measure.However, we seem to forget or WISH to forget another pre Big Bang theory…….GOD.
Where did God come from ?If he is perfect he is eternal no beginning or end.The Mona Lisa may be considered a perfect piece of art but it’s origins were a crude piece of canvass and selection of oils.Its state was only improved upon.
PERFECTION thus by definition is eternal.GOD would explain EVERYTHING.QUITE NEATLY…….perhaps scientists need to be brave and accept an alternate truth just as Gallileo and Darwin made many of faith to be brave in thought!
I can hear all your groans from here but please do not dismiss out of hand…
July 8th, 2008 at 9:26 am
Science will most likely never be able to answer the question of why anything exists at all. That is the domain of philosophy.
August 11th, 2008 at 1:00 am
@Chris Stewart:
I agree, if you look at the definition of science, it about every force that is visible or whos effects are visible. Fair enough. Although, it fails to address the possibility that humans cannot possible measure some things or imagine things that exist but we don’t know. I find it a bit strange when scientists say, earth was the only planet to have a fine tuned environment for life. Well, what if life was fine tuned through evolution to fit earth? the same argument applies to extra terrestrial beings, why can’t a different life form exist on mars? can’t a different kind of life evolve that we cannot even begin to comprehend?
August 15th, 2008 at 12:34 pm
We as humans can’t comprehend that time is truly infinite. I’ll quote The Matrix, “Everything that has a beginning, has an end”. That’s all we can understand at this point in time because it makes us feel comfortable and safe.
In my opinion, there was definitely a Big Bang, and before that there was a “Big Crunch.” Before that Big Crunch was a long period of time where the universe was in a state similar to what we see now. Yes, the universe is expanding now, it seems like, but years from now, it will stop expanding and will begin to contract to create that new “Big Crunch” only to begin to create a new universe with a new Big Bang.
Maybe humans will never understand infinity because in our world, everything that does start eventually has to end and that’s what we know.
August 15th, 2008 at 12:41 pm
…but now that I think about it, maybe my opinion falls into this “safety zone” i speak of because that’s what makes me comfortable. Making the excuse that time is infinite, and, because I am not a religious man, I feel comfortable telling myself that there was never a single force that created the building blocks of the universe and “space” itself. There was never a single force that had the immense power to do that, or take everything we know away with the snap of the fingers.
Way to contradict myself!
August 15th, 2008 at 7:08 pm
How about multiverses. Each expands from its own big bang. Sometimes they are close enough to each other that they expand into each other’s space. Where they overlap the black hole seed of a new big bang begins to form.
Maybe that seed begins to pull from each of the two “universes” and collapses from its own gravity until it hits a critical point and you get a new big bang.
Or maybe it can never reach the critical point, because too much of the matter from the previous 2 universes has dissipated out in the other direction. Remember they had to reach that same critical mass in order to have exploded in the past. In that case, maybe a third universe comes in as a trigger, spinning like a buzz saw.
In the 2-universe case, you might expect a disk shaped signature in the new universe, representing the gradual overlap of the 2 previous universes. Or you might find 2 poles, representing the central bulk of each of the 2 previous universes that got sucked in more rapidly at the last minute.
In the 3-universe (trigger case), you might expect a disk plus some other mass coming in at an angle.
In any case, it seems we would expect low entropy right after the big bang (as observed) because the crunch has pressed clumpy matter into more homogeneous plasma. After the bang, it spreads out, cools off, and gets clumpy again.
August 17th, 2008 at 11:48 am
god is the energy before the big bang. intelligent energy.
September 10th, 2008 at 7:47 pm
im 12 and when i read about tise it was the coolets thing i ever heard of