New Proposal for Probing What Came Before the Big Bang

Before the Big Bang CMB Timeline

A representation of the timeline of the universe. Credit: WMAP Collaboration

Most everybody is familiar with the Big Bang — the notion that an impossibly hot, dense universe exploded into the one we know today. But what do we know about what came before?

In the quest to resolve several puzzles discovered in the initial condition of the Big Bang, scientists have developed a number of theories to describe the primordial universe, the most successful of which — known as cosmic inflation — describes how the universe dramatically expanded in size in a fleeting fraction of a second right before the Big Bang.

But as successful as the inflationary theory has been, controversies have led to active debates over the years.

Some researchers have developed very different theories to explain the same experimental results that have supported the inflationary theory so far. In some of these theories, the primordial universe was contracting instead of expanding, and the Big Bang was thus a part of a Big Bounce.

Some researchers — including Avi Loeb, the Frank B. Baird, Jr. Professor of Science and chair of the Astronomy Department — have raised concerns about the theory, suggesting that its seemingly endless adaptability makes it all but impossible to test.

“The current situation for inflation is that it’s such a flexible idea … it cannot be falsified experimentally,” Loeb said. “No matter what result of the observable people set out to measure would turn out to be, there are always some models of inflation that can explain it.” Therefore, experiments can only help to nail down some model details within the framework of the inflationary theory, but cannot test the validity of the framework itself. However, falsifiability should be a hallmark of any scientific theory.

That’s where Xingang Chen comes in.

A senior lecturer in astronomy, Chen and his collaborators for many years have been developing the idea of using something he called a “primordial standard clock” as a probe of the primordial universe. Together with Loeb and Zhong-Zhi Xianyu, a postdoctoral researcher in the Physics Department, Chen applied this idea to the noninflationary theories after he learned about an intense debate in 2017 that questioned whether inflationary theories make any predictions at all. In a paper published as an Editor’s Suggestion in Physical Review Letters, the team laid out a method that may be used to falsify the inflationary theory experimentally.

In an effort to find some characteristic that can separate inflation from other theories, the team began by identifying the defining property of the various theories — the evolutionary history of the size of the primordial universe. “For example, during inflation, by definition the size of the universe grows exponentially,” Xianyu said. “In some alternative theories, the size of the universe contracts — in some very slowly and in some very fast.

“The conventional observables people have proposed so far have trouble distinguishing the different theories because these observables are not directly related to this property,” he continued. “So we wanted to find what the observables are that can be linked to that defining property.”

The signals generated by the primordial standard clock can serve this purpose.

That clock, Chen said, is any type of massively heavy elementary particle in the energetic primordial universe. Such particles should exist in any theory, and they oscillate at some regular frequency, much like the swaying of a clock’s pendulum.

The primordial universe was not entirely uniform. Quantum fluctuations became the seeds of the large-scale structure of today’s universe and one key source of information physicists rely on to learn about what happened before the Big Bang. The theory outlined by Chen suggests that ticks of the standard clock generated signals that were imprinted into the structure of those fluctuations. And because standard clocks in different primordial universes would leave different patterns of signals, Chen said, they may be able to determine which theory of the primordial universe is most accurate.

“If we imagine all the information we learned so far about what happened before the Big Bang is in a roll of film frames, then the standard clock tells us how these frames should be played,” Chen explained. “Without any clock information, we do not know if the film should be played forward or backward, fast or slow — just like we are not sure if the primordial universe was inflating or contracting, and how fast it did that. This is where the problem lies. The standard clock put time stamps on each of these frames when the film was shot before the Big Bang, and tells us what this film is about.”

The team calculated how these standard clock signals should look in noninflationary theories, and suggested how to search for them in astrophysical observations. “If a pattern of signals representing a contracting universe were found,” Xianyu said, “it would falsify the entire inflationary theory, regardless of what detailed models one constructs.”

The success of this idea lies in experimentation. “These signals will be very subtle to detect,” Chen said. “Our proposal is that there should be some kind of massive fields that have generated these imprints and we computed their patterns, but we don’t know how large the overall amplitude of these signals is. It may be that they are very faint and very hard to detect, so that means we will have to search in many different places.

“The cosmic microwave background radiation is one place,” he continued. “The distribution of galaxies is another. We have already started to search for these signals and there are some interesting candidates already, but we still need more data.”

This research was supported with funding from the Black Hole Initiative at Harvard University and the Center of Mathematical Sciences and Applications, Harvard University.

Reference: “Unique Fingerprints of Alternatives to Inflation in the Primordial Power Spectrum” by Xingang Chen, Abraham Loeb and Zhong-Zhi Xianyu, 17 Feb 2019, Physical Review Letters.
DOI:  10.1103/PhysRevLett.122.121301

34 Comments on "New Proposal for Probing What Came Before the Big Bang"

  1. Well now

    • “That clock, Chen said, is any type of massively heavy elementary particle in the energetic primordial universe.”. Perhaps this is something Lost in translation, but no elements would come to exist for quite some time until after inflation and the big-bang itself, Did they mean “sub-atomic” particles?

  2. What was there at the very beginning?
    Why was it there?

    • Nobody knows, we have only theories. Respect the WHY, this is not a scientific question, but philosophical or metaphisical, but if you insist I will tell you that the most important principle is the energy conservation. They was there because the energy can’t be created nor destroyed. It was because it already existed. Why existed? Nobody knows. If someone assures you otherwise, they will be cheating you.

      • It can’t “always exist” because it is running down. Therefore it had to start existing at some point and will eventually cease to exist. Everything natural has a cause, so … what caused it to be there in the first place?

      • I can live with doubt and uncertainty and not knowing. I think it’s much more interesting to live not knowing than to have answers which might be wrong. – Feynman

  3. Md sohrab alam | April 23, 2019 at 9:54 am | Reply


  4. Anon Y. Mouse | April 23, 2019 at 2:00 pm | Reply

    I think the universe has always been here, but what we call the “big bang” was a explosion on a cosmic level who’s remnants are found in the radiation that was discovered in 1964.

    • Dumi Mkokstad | May 17, 2020 at 12:30 pm | Reply

      i was thought the univers is like ball, with latitude and longititude but the earth is heal by nice sounds

  5. The big bang theory is just that a theory nothing no more it is a false teaching of creation There’s only one supreme being who created man and this universe and everything in it big bang is a way to take God out of the equation Man was created in his image we are divinely created complex beings superior to any other living thing on earth just wait and see for yourself you will meet him someday and you will surely know the truth because 100% certain you are going back to the dirt of this earth from which you were created that is truth it’s a fact your alive one day and then bang your dead only big bang your going to know because it’s real not a theory.

    • Allah, the almighty will definitely reward and punish as the day of judgement comes and yes, it is for sure for all the human beings Believers Or non-Believers…

    • Yes, big bang is a theory, written on screens and paper. Like the Bible also written on paper, it isn’t a theory it is just a story you like and chose to believe. How do you know and prove the Bible is a TRUE teaching of creation? There is mountains of EVIDENCE that evolution exists not some made up God.

      • …just a surely as we are not descendants of apes. I’ll stick with the sci evidence. Oh, and which god exactly created your universe?

    • Nope! Now that is some crazy stuff to believe. Also, I’m pretty sure that Geckos are the most superior beings since they can use the Casimir effect to stick to walls.

    • bro i swear this comments are worse than Reddit and Twitter combined.💀

    • The problem is that you haven’t bothered to even find out what a “theory” means in science. That’s intellectual ineptitude.
      God is out of the equation not because of the Big bang, but because he (or books written in his name) explained nothing; and what little “evidence” were presented were shown to be wrong. Someone who claims to be a creator ought to know the basics of his supposed creation.

  6. You are a nasty degenerate , put the gun in your nasty mouth and pull the trigger

  7. Benjamin Sanborn | May 21, 2019 at 4:52 am | Reply

    Yes a loving God is possible. The god of the bible is psychotic and was told to men in desert huts by a voice in head. Rules on slavery. Etc. I hope a loving God exists words twisted by politics etc during 2k years new testament. Also he has been quiet. If omnipotent he knew Eve would eat apple. He knows the whole ending results of each action. Omnipotent means he knows u won’t go to heaven due to x events. And we at least do finite punishment not eternal hell. When he loves u
    If u go to heaven but family ends up in hell is it really heave

    • What bugs me is that he creates the universe 6000 years ago, and then reveals himself only 2000 years ago. So those poor humans who died in the first 4000 years went straight to hell. How is that just?

  8. But Hadn’t The Big Bang Theory finished?

  9. . I hope a loving God exists words twisted by politics etc during 2k years new testament. Also he has been quiet. If omnipotent he knew Eve would eat apple. He knows the whole ending results of each action. Omnipotent means he knows u won’t go to heaven due to x events. And we at least do finite punishment not eternal hell. When he loves u

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