How do we know the Universe had a beginning?

I think it’s all days and nights of Brahma…

Sure it’s possible, but how can our puny, human brains comprehend that?

@bookish1 Could be. Just could be.

@Self_Consuming_Cannibal Just as easily as they can grasp the explanation, “In the beginning there was nothing, then it exploded.”

Hubble’s Law would tend to suggest that the universe had a definite beginning, as would the mere existence of the CMB.

Sure, there’s the epistemological issue of of what happened before the end of the quark-gluon plasma phase, but the evidence of expansion seems solid enough for us to make clear inferences as to what went before.

@the100thmonkey Granted, but that takes us back to this beginning. We know there are lots of things that go through multiple cycles of beginning. What establishes for us that the Universe is not one of them, and that before this beginning, it was in some other form that transitioned to what we observe today?

@ETpro But I don’t think we can grasp that. That’s why we are spending billions (perhaps trillions?) of dollars trying to figure all this stuff out.

@Self_Consuming_Cannibal Yeah, well I guess it’s in the billions. And we may never come to the full understanding of how the Universe got here, or whether it has always existed. But our research did really spike development of the digital age, and give us neat toys like cell phones. And who knows if our efforts at space exploration my not some day spell salvation for the entire human species? Sooner or later, our planet will face a cosmic cataclysm such as a collision with a rouge planet, a wandering black hole, or some other sort of doom that will end all life on Earth. So it’s worth spending a bit of our largess today in hopes of developing the means to move to better quarters before these are hit by the cosmic wrecking ball.

*rogue
rouge is a colour.

^ ^ Ha! Danged spell checker. Too late to edit now.

@ETpro Perhaps our quest will save our species. That would be a nice change. While we may have come along way with heart transplants and other medical wonders, it’s too bad that in the mean time we’ve also come up with nuclear bombs as well.

You are making too many assumptions based on our human concept of time.

@Self_Consuming_Cannibal That’s a possibility, I guess. Then again, aliens may just be here to watch when the hour of doom comes. Who knows but what its just some teens who have borrowed dad’s flying saucer to come get it all on video. In their world, planetary destruction videos always go viral.

@cazzie OK, care to elaborate? Who’s making (presumably) false assumptions, and what are they assuming?

To assume a ‘beginning’ is to assume a scale of time in a system we understand. It is cyclical and eternal and simply goes through constant entropy with things combining and falling apart. Roger Penrose has some good books. (Cycles of Time, for example) I don’t bother with Brian Greene any more.

Here is an audio lecture by Penrose:

http://www.newton.ac.uk/webseminars/pg+ws/2005/gmr/gmrw04/1107/penrose/

@cazzie Huh? The whole question is asking if assuming a beginning is right or wrong. Thanks for the book reference. I will follow up on them. Will I find proof of the assertion that time is infinite and cyclical in doing so?

Here’s a review of Cycles of Time by mathematician, Peter Woit, PhD. I’m not sure if you can follow his review. It’s above the heads of most of us. But suffice to say he sees some pretty serious flaws in Penrose’s assertion.

…how can we have any confidence that this Universe had any beginning? Isn’t it just as possible that it is infinite and cyclical?

The Standard Model of physics has established that the universe emerged from a big bang. Whether this was a one-time event or it cycles between “bangs” and “bounces” is unknown. Until the late 1990s it was thought the expansion would slow down and might reverse into a big crunch. Now we know the expansion is accelerating so the crunch scenario looks unlikely. Eventually, with continued expansion, formation of new stars & galaxies will end as thermal equilibrium and “heat death” are approached.

Bear in mind that the big bang model itself is established fact, resting on three pillars of evidence: (1) Uniform expansion, discovered by Hubble in the 1920s; (2) Cosmic microwave background, as predicted by theory & discovered by Penzias & Wilson in 1964; (3) Relative abundances of hydrogen & helium, as predicted by theory (I’m not sure of the details here) & confirmed by observation to a high degree of precision.

A newer idea is that our observable universe is just one bubble in a large (infinite?) higher-dimensional fractal structure with new “baby universes” constantly forming even as our winds down. At present this appears unknowable—but then so did much of what we know today seem unknowable in previous centuries.

@gasman Thanks. That’s a pretty good capsule view of our understanding to date.

@ETpro I guess that would make an interesting viral video. I wonder if they have youtube. I guess if they did they could just watch the video by typing in, “Watch the destruction of the alien race” in their search bar. lol

We don’t, because we don’t know what happened before the 10^-43th second of our universes’s life.

Actually, on reflection, doesn’t this question invoke an infinite regress as a premise?

If that were the case, and I were a positivist, I’d be inclined to suggest the question doesn’t make sense.

Sorry, I’ve been getting back into philosophical logic and early 20th century empiricism recently

@the100thmonkey No, not if the evidence shows that infinite regression is not the case. But is infinite regression any less logical than “In the beginning there was nothing, then it exploded?”