• Question: when will the universe end and how?

    Asked by bradwrf to Adam, Geoff, Rob, Sheila, Suzie on 15 Mar 2011 in Categories: .
    • Photo: Adam Tuff

      Adam Tuff answered on 14 Mar 2011:

      There are many different theories as to how it will end, and they all depend on how much matter there is in the universe. Some people think the universe is as it is, and always will be – in this case the universe will never end, however this doesn’t agree with the big bang, which says the universe had a beginning.

      Another idea is the “open model” of the universe, in that the universe will keep expanding forever from the big bang. Again, this means it will never end.

      The last model, and my favourite, is the “closed model”, this says that there is so much matter in the universe that eventually gravity will everything back together again in what is known as the “big crunch”. I don’t think anyone knows how long it would take for the big crunch to happen!

      Great question!

    • Photo: Suzie Sheehy

      Suzie Sheehy answered on 14 Mar 2011:

      I have to say the best discussion of this was on last week’s “Wonders of the Universe” by Brian Cox on the BBC – it’s probably still on iPlayer!
      But, in the meantime:
      All the stars will eventually die in one way or another and the universe will continue to expand until there is no matter left, just radiation. A bit depressing, really!

    • Photo: Robert Simpson

      Robert Simpson answered on 15 Mar 2011:

      I actually have a blog post all about this (http://orbitingfrog.com/post/3424306221/ways-to-end-the-world). My favourite ways to end the Universe are:

      1) The Big Crunch – like the anti-big bang where everything collapses in together into a point.

      2) The Big Rip – where the Universe expands faster and faster forever until it tears itself apart.

      3) Death by Uncertainty Principle – Nothing is impossible, just highly improbable. (As fans of the Hitchhiker’s Guide are aware.) That is what Heisenberg ended up stating about the Universe thanks to quantum mechanics. Given enough time – say an infinitely long time – incredibly unlikely things can happen. But given if the universe is infinitely large and goes on forever then eventually everything that CAN happen, WILL happen, including a host of terrible things like a giant cat that uses the Earth like a bauble or a massive death that blasts us out of existence. It won’t happen – but technically and infinitesimally, it could.

    • Photo: Sheila Kanani

      Sheila Kanani answered on 15 Mar 2011:

      No one really knows the answer to either of those questions!

      I’ve copied my answer to another question here:

      The latest ideas on the fate of the universe (as far as I know) are still:
      1) Ever expanding
      2) The big crunch

      The evolution of the universe is determined by a struggle between expansion and the pull (or push!) of gravity. The current rate of expansion is measured by the Hubble Constant, while the strength of gravity depends on the density and pressure of the matter in the universe.

      If the pressure of the matter is low, as is the case with most forms of matter we know of, then the fate of the universe is governed by the density.

      If the density of the universe is less than a critical density, then the universe will expand forever. Gravity might slow the expansion rate down over time, but for densities below the critical density, there isn’t enough gravitational pull from the material to ever stop or reverse the outward expansion. This is also known as the “Big Chill” or “Big Freeze” because the universe will slowly cool as it expands until eventually it is unable to sustain any life.

      If the density of the universe is greater than the critical density, then gravity will eventually win and the universe will collapse back on itself, the so called “Big Crunch”. In this universe, there is sufficient mass in the universe to slow the expansion to a stop, and then eventually reverse it.

      Recent observations of distant supernova have suggested that the expansion of the universe is actually accelerating or speeding up which implies the existence of a form of matter with a strong “negative” pressure. This strange form of matter is also sometimes referred to as the “dark energy”.

      We believe that unlike gravity which works to slow the expansion down, dark energy works to speed the expansion up. If dark energy exists, and plays a significant role in the evolution of the universe, then in all likelihood the universe will continue to expand forever.

      There is a growing consensus among cosmologists that the total density of matter is equal to the critical density, so that the universe is spatially flat. Approximately 3/10 of this is in the form of “non-baryonic” dark matter, while the remaining 7/10 is thought to be in the form of “dark energy”. If this is true, then dark energy is the major driving force behind the fate of the universe and it will expand forever exponentially.

      I quite like the idea of a Big Crunch, because then there could be a new Big Bang and it can all start again! This theory is called the Big Bounce 🙂

      What do you think is going to happen?

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