Will the universe contract

Alain De Vos

Alain De Vos

The universe expands. And it expansion increases. But will there be a time when the universe contracts ? And returns to a singularity to form a new universe ?
 
Alain De Vos said:
But will there be a time when the universe contracts?
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I think physicists are still not 100% sure if the universe will contract in a big fiery end or expand forever and become a very sparse cold and empty place. I believe they are leaning towards the latter.

PBS Spacetime videos on the topic are generally quite engaging.

Stephen Hawkins' The Universe In a Nutshell is also a very good read (it follows on from the Brief History of Time).
(my main advice is get the one with illustrations ;))
 
About 40 years ago, the textbook answer was: Given that the universe is expanding rapidly, and does not contain enough stuff for gravity to pull it back together, it will continue expanding forever. Meaning things will get boring, cold and lonely.

Today, with dark matter/energy, the answer has become less clear. We now know that there is a lot more stuff than we can see or measure. But we don't know what that stuff is, nor are we really sure how it interacts (for example by gravity). But I haven't heard any serious theory of re-collapse.
 
Pure amateur and ill-informed speculation, but given that there are stars out there that seem to be older than the Big Bang (which yes, is controversial), this hints at there having been one or more universes before ours. And that the Big Bang wasn't as big as originally thought. And therefore, perhaps big bangs are more cyclic rather than a once-ever kind of event. If so, then we might expect the universe or parts of it to contract again in the future for another bang.
 
dbdemon said:
Pure amateur and ill-informed speculation, but given that there are stars out there that seem to be older than the Big Bang (which yes, is controversial), this hints at there having been one or more universes before ours. And that the Big Bang wasn't as big as originally thought. And therefore, perhaps big bangs are more cyclic rather than a once-ever kind of event. If so, then we might expect the universe or parts of it to contract again in the future for another bang.
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I'm not a fan of space, but it's the first time I've heard this.
 
People have speculated about such things for thousands of years, even multiple universes! See for instance https://en.wikipedia.org/wiki/Hindu_cosmology

The Hindu texts describe innumerable universes existing all at the same time moving around like atoms, each with its own Brahma, Vishnu, and Shiva.

I tend to think even with our modern Scientific methods and detailed experimentally gained knowledge and theories all we can do is speculate about such things.
 
YYY__ said:
I'm not a fan of space, but it's the first time I've heard this.
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The cyclic idea idea was when we still figured the universe would collapse back into itself again. So you get this "pulsating" universe, big bang, expansion, contraction, big crunch, big bang, expansion, contraction, etc. There are also several ideas floating around regarding a "multiverse", with each universe created inside a "bubble". All very theoretical of course, there's no way we could ever prove the existence of a "multiverse".
 
Seeing that all imagining of past or future is mythology:

"-> The life span of the universe is one "maha kalpa". i.e. 311.04 trillion human years. This time span is also the duration of one breath of "Vishnu" (the ultimate god in hindu religion). When he exhales, thousands of universes emerges and one "Brahma" is born in each universe. When "Vishnu" inhales, all universes get sucked and Brahma dies.
-> This cycle is non-ending and eternal. Thats why "Vishnu" is considered eternal in Vedic Science (or religion)."

Age of Universe according to Vedas
 
Paul Floyd said:
Is the universe a 3-sphere? If so it will just go round and come back again.
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As far as we've been able to measure the universe is "flat". It could still be curved though (positive or negative curve), but we may not be able to measure it.
 
Flying saucers? The good 'ol Reichsflugscheibe?

SirDice check out Anton Petrov, he also has good stuff. Or Sabine Hossenfelder. That's where "the telephone will ring".

And if the universe will collapse? No idea. Maybe there are overlapping universes, created over and over and all we can see from them is dark matter. But how long till we will even measure an effect here on earth either way? That will be long after the sun went nova, the galaxy melted up in a big big mess and nobody remembers out names. When the thing is decided, please wake me up. I'll be sleeping in a sunken city, be sure not to ring up the neighbors.
 
ralphbsz said:
About 40 years ago, the textbook answer was: Given that the universe is expanding rapidly, and does not contain enough stuff for gravity to pull it back together, it will continue expanding forever. Meaning things will get boring, cold and lonely.
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I remember this being called the "Big Whimper" scenario for the end of the universe. It was the accepted likely scenario when I last read about this decades ago.

ralphbsz said:
Today, with dark matter/energy, the answer has become less clear. We now know that there is a lot more stuff than we can see or measure. But we don't know what that stuff is, nor are we really sure how it interacts (for example by gravity). But I haven't heard any serious theory of re-collapse.
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The Big Crunch is back in vogue, it seems:
www.livescience.com

Dark energy could lead to a second (and third, and fourth) Big Bang, new research suggests

Scientists have proposed a way that the universe could stop expanding, ending in a 'Big Crunch' that resets space and time as we know it.
www.livescience.com www.livescience.com
 
From a purely philosophical point of view I can't quite say whether it's less troubling to say 1) the universe had a once-ever beginning in the singularity (in which time didn't exist) and then a mysterious Big Bang, or 2) that the universe (i.e. matter/energy - same thing, according to Einstein!) has simply always existed, i.e. without beginning or end, for eternity (which could be a way of seeing the "pulsating universe").

Personally, I'm leaning towards the latter, but it's hard to wrap your head around this.
 
Paul Floyd said:
Is the universe a 3-sphere? If so it will just go round and come back again.
Click to expand...
this is currently unknown, but there was theories that our universe might be a certain manifold, for example torus. what exact geometry is a case of refined measurements ( for example of CMB ) which will tell if the space is flat or curved. With years passed i tend to not accept inflation theory. I like Neil Turok approach more. https://insidetheperimeter.ca/a-mirror-universe-might-tell-a-simpler-story-neil-turok/
 
All experimental measurements show the universe is flat. Off-course the surface of one very-very-very-big-torus is also flat.
 
Jose said:
The Big Crunch is back in vogue, it seems:
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Yes, every possible theory is back in vogue to explain astrophysics. That includes multiverses, branes, cyclical collapse, strange topology, dark energy, and who knows what else. Similar things are happening in the (closely connected) field of particle physics: While we have now created the Higgs in the lab, our understanding of why particles are the way they seem to be is still frustratingly incomplete. In particular, weak interactions and neutrino physics remains an enigma. This also leads to the rise of a huge quantity of theories, which all get published on the web, and many of them also in respectable journals.

I'm not saying that those theories are wrong, but I definitely know that most of them must be, and perhaps all.

I just got a really good new book from the library: Cahn and Quigg "Grace in All Simplicity". It explains the history of particle (and astro-) physics since the 1700s. Given that I have worked in that field in the distant past, I actually know some of the characters personally, and many of them from stories. It has a wonderful vignette about how culture has changed. In the early 1930, the British physicist Paul Dirac created equations that describe the interaction of a relativistic electron with electromagnetic fields, and discovered that his theory predicted the existence of the antiparticle of the electron. Today, we know that particle to be the positron (and it was discovered by Anderson in cosmic rays a few years later). But at the time, Dirac didn't want to identify the new particle as such, and instead posited that it was the proton (long known), and pointed out that electron and proton having different masses remains an open question. Decades later, someone asked Dirac why he didn't just claim to have predicted a new particle, and instead identified the solution of his theory with an existing one. The answer is, in a nutshell: While publishing a good clean theory that can explain the behavior of the electron is clearly scientific progress, in those days (the 1930s), speculating about the existence of a particle that has never been seen was considered bad style.

Similarly, a few years later Pauli explained the missing energy and momentum in beta decay by positing a new particle, the neutrino, which leaves the reaction unseen. To get around the obvious criticism "you can't just go and hypothesize a particle that doesn't exist", his theory cleanly and carefully explains that the properties of the neutrino make it all but invisible, explaining why it has never been observed. Again: don't go and predict things that don't exist, because you will make a fool of yourself if they aren't found.

In both these cases, the predictions were found to be true: Anderson found the positron within a few years, and my old boss Fred Reines discovered the neutrino in the 1950s. The reason that Dirac and Pauli are heroes is: They took a measured risk of going out on a limb. An even more fun example was the "November revolution": People had been predicting the existence of a 4th quark (based on good logical reasoning), and within a few years it was found at Stanford (and I'm still in touch with people who helped with that, on a weekly basis).

Today's scientific culture is different. It is considered completely acceptable, and even honorable, to propose completely crackpot models that have no testable predictions. Because of the large number of people working in the field, and the near complete lack of new observational data, the culture is to throw things against the wall, and see what sticks. To some extent that is a good thing: theorists no longer have to hide their good ideas for fear of ridicule. To a large extent it is a bad things: thousands of man-years have been and are being wasted on working out the details of theories (such as strings) that have yet to yield any useful or testable predictions, and will likely fall by the wayside eventually. A toroidal universe is likely to be in that category.
 
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