Big Bang News Physics

Can physics tell us if time had a beginning?

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Physicist Ethan Siegel argues

Did time have a beginning? We not only don’t have the answer, we don’t have the prospect of observations that could tell us, and our current theories only tell us where our predictive power breaks down, not what the answer is. So we have the same three possibilities that philosophers and theologans have pondered for as long as history has been recorded: time is finite, time is infinite, or time is cyclical. The only thing we know is that if there was a singularity in the past, it didn’t have anything to do with our Hot Big Bang that every particle of matter-and-energy in our observable Universe is traceable to.

And unless we figure out a new way to gain information about what happened before the Universe observable to us existed in any meaningful sense, the answer may forever be beyond the reach of what is knowable.

But if time is infinite in the past, doesn’t that violate Hilbert’s Hotel? In which case, logic will tell us if physics doesn’t? Thoughts?

See also: What would the universe look like, if the past was infinite? and The Science Fictions series at your fingertips (cosmology).

Hilbert’s Hotel:

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6 Replies to “Can physics tell us if time had a beginning?

  1. 1
    VunderGuy says:

    Isn’t ‘time is cyclical’ just a specific way time could be infinite?

  2. 2
    Querius says:

    If time is cyclical, then it is finite . . . unless causality doesn’t exist, in which case we can know nothing.


  3. 3
    jstanley01 says:

    A commenter argues back:

    Ethan, Ethan, Ethan. For the past 40 years the term “the Big Bang” has been used for the event at the very beginning of the universe, the event beginning at TIME ZERO. So no, according to the thinking of modern cosmologists, a period of inflation did NOT occur “after” the Big Bang, but occurred after that event (or as part of that event). You are confusingly modifying the term “Big Bang” if you redefine it as anything occurring after time zero. The Big Bang is the beginning, not something after the beginning. This post is a prescription for confusion (in contrast to your many other very helpful and clarifying posts).

  4. 4
    bornagain77 says:

    “Every solution to the equations of general relativity guarantees the existence of a singular boundary for space and time in the past.”
    (Hawking, Penrose, Ellis) – 1970

    Big Bang Theory – An Overview of the main evidence
    Excerpt: Steven Hawking, George Ellis, and Roger Penrose turned their attention to the Theory of Relativity and its implications regarding our notions of time. In 1968 and 1970, they published papers in which they extended Einstein’s Theory of General Relativity to include measurements of time and space.1, 2 According to their calculations, time and space had a finite beginning that corresponded to the origin of matter and energy.”3
    Steven W. Hawking, George F.R. Ellis, “The Cosmic Black-Body Radiation and the Existence of Singularities in our Universe,” Astrophysical Journal, 152, (1968) pp. 25-36.
    Steven W. Hawking, Roger Penrose, “The Singularities of Gravitational Collapse and Cosmology,” Proceedings of the Royal Society of London, series A, 314 (1970) pp. 529-548.

    Evidence For The Big Bang – Michael Strauss

  5. 5
    VunderGuy says:


    How does that work? If it’s a cycle, couldn’t it be an infinite cycle?

  6. 6
    Querius says:

    Cycles repeat, so what happens when you get back to the beginning of a cycle of time? It’s the same place in time with the same events that then caused the other events, and so on, until you start the loop over again.

    Imagine standing dominoes on their ends in circle. Tip one so it starts a chain reaction until it reaches the starting point and then . . . it stops. There are no new events.


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