Let's Talk Physics

A stochasticly updated blog about interesting topics in Physics & Astronomy

How it’s All Going to End: The Lights Go Out (Part 5)

I’ve talked about the Earth being swallowed by the Sun, punctured by meteors, consumed by black holes or destroyed by the merger with the Andromeda galaxy. And in each case, there’s been some way for humanity to survive – jump ship and find a new planet to live on. The outcome of today’s topic is a lot more bleak. Today I’m going to talk, not about the end of the Earth, the Galaxy or humanity, but instead about the end of the Universe.

As quite a lot of modern physics does, this story is going to begin with Einstein. And again, it’s his famous theory of General Relativity that’s going to start us on our way. You see, when Einstein originally derived his field equations, he found that the Universe was unstable, that its size was changing. But physicists at the time believed that this wasn’t true, they believed the Universe was a static place, neither getting larger or smaller, but of constant size. So Einstein added a term onto his equation which didn’t change any of the solutions, but predicted that the Universe was stable.

Einstein after figuring out how to describe the Universe as stable

Einstein after figuring out how to describe the Universe as stable

A few years later, a physicist called Georges Lemaître proposed that the Universe was actually expanding, and gave an estimate for the rate of this expansion. In 1929, Edwin Hubble confirmed this from observational data, and gave a more accurate value for this data. Since the Universe was expanding, and not of constant size as previously suspected, this mean that Einstein’s extra term in his field equations wasn’t needed. The term was removed from his equations and returned to their original form, and  Einstein went on to call this greatest blunder of his life, as if he hadn’t added this extra term to his equations, he would have predicted the expansion of the Universe before anyone else had even thought of it.

Einstein not amused after realizing he just missed out on having another thing named after him

Einstein not amused after realizing he just missed out on having another thing named after him

So, the idea that the Universe is expanding leads us to believe that the Universe has to start somewhere, and as something. That something is known as the Big Bang, and from Hubble’s constant, which tells us the approximate age of the Universe, we figure this Big Bang happened about 13.7 billion years ago. At this time, everything in the known Universe was condensed into a single point of infinite temperature and contained all of the mass in the Universe, and after the big bang, the “edges” of the Universe began moving away from each other. Below is a rough timeline to how the Universe has evolved so far (plus some spoilers as to where it’s going).

Expansion of Unieverse

Then, in 1998, the story took another twist. Saul Perlmutter, Brian P. Schmidt, and Adam G. Riess dicovered that, not only is the Universe expanding, but the rate of this expansion is accelerating! This has far reaching consequences for the existence of dark energy and many other exotic topics in physics, but for the end of the Universe, this spells trouble. You see, when a star ends its life, and leaves behind a core of Iron or electrons, neutrons or even a black hole, it still returns some matter (mainly Hydrogen and Helium and other unused fuel from its lifetime) back into the Universe. This spare material generally goes back into forming new stars, or planets.

Now, here is where there are 2 (and now maybe 3) schools of though.

1. The Big Freeze

There is a school of thought that believes that the Universe will keep on expanding at a faster and faster rate forever. This means, eventually, all of the stars will end up so far away from each other that the material from the death of a star will never be used to create a new star, or if it does, that star won’t be very big, and will use up all of this fuel without returning anything to the Universe. All it will leave is a black hole or a neutron star, something which can’t create a new, bright hot star. So this means there can only ever be a finite number of stars during the life time of the Universe, and there will come a time when there are no stars anywhere! Also, the expansion of the Universe isn’t essentially due to everything moving away from each other. It’s actually a lot more complicated. What’s really happening is the space in between all of the objects in the Universe is getting bigger.

If you and I were floating beside each other in space and wait for a very, VERY long time, the space in between us would get bigger and push us apart. To me, I’d see you start to move away from me, and with the larger amount of space now in between you and me, the bigger the expansion, the faster you seem to be moving away, which leads to even more space us, making you go faster relative to me (which is why I think you are accelerating away from me). This is actually what the expansion of the Universe means.

So in this Universe, where all of the stars are starting to die and no new ones are being born, the stars are also increasingly moving away from each other. And eventually, everything will get so far away from everything else that if you were to stand on a planet in the Universe, you wouldn’t see a single star in the sky. Everything would be gone. The Universe would literally have become an empty wasteland. Devoid of light, aliens, everything.

The Universe after the Big Freeze

The Universe after the Big Freeze

2. The Closed Universe Model

Another school suggests the Universe is cyclic. What they think will happen is eventually, the rate of expansion of the Universe will stop accelerating, and actually start to collapse back in on itself! Which means, everything will start getting clustered together quite rapidly. Look back up at the figure showing the expansion of the Universe from the Big Bang to now and then beyond. And then imagine time going the other way. Everything would condense back into a single point of infinite temperature and density. And then what? Will, hopefully, another Big Bang, and a new Universe can begin.

3. A Universe within a Universe

This ones a bit new. And by a bit new, I mean since Monday, February 18th, 2013. Actually, you mightn’t even be able to call this a school of thought, more of an idea at the moment. Last Summer, researchers in CERN found what they believe to be the Higgs Boson (a discovery which warrants its own post in the future). On Monday, scientists from the Fermi National Accelerator Laboratory in Illinois, America proposed that the current mass of the Higgs Boson suggests that (after doing some calculations) the Universe is unstable (which we knew) and has a finite lifetime (which we didn’t know) until this instability catches up with us. And what does that mean? Well, they think that in roughly 10 billion years, somewhere in the Universe, a bubble will pop into existence. And in this bubble, there will be a new, different Universe, which will begin expanding into and consuming our own. Now was I said, this is very, very recent (news article is here) and might not be true. But it doesn’t make it not an interesting idea.

So that’s it. We might be able to avoid comets, black holes, galaxies, and stars, but this, there seems, there will be no escaping. The end of the Universe is the end of our story. Unless we find a way to build our own stars (the Big Freeze) or travel between Universes (A Universe within a Universe). As for the cyclic model, I can’t see a way out of that one, but maybe you can. If you do, comment and let me know!


Mondays post will be about are we alone in the Universe (as requested by Stephen Walsh). If anyone has ideas for next Thursday, please comment away.

Also, join the mailing list on the right of this article and share this article with friends if you liked it.


About irishphysicist

I'm a PhD student with the Departments of Physics in University College Cork, Ireland and University of Notre Dame, Indiana. I want to try and bring astrophysics to the public, and also would like world domination. But that's a story for another day.

2 comments on “How it’s All Going to End: The Lights Go Out (Part 5)

  1. Thomas Kelly
    March 4, 2013

    I find the Big Freeze to be the most interesting. Roger Penrose recently brought out some interesting work showing how under certain conditions, an infinite, bleak, cold universe and a Big Bang singularity are ultimately the same state.

  2. Pingback: Famelab 2014 (It’s time for a comeback) | Let's Talk Physics

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This entry was posted on February 21, 2013 by in Astrophysics and tagged , , , , , , , , , , .
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