General relativity also doesn’t explain the future of the universe. There are interesting theories that say the universe is going to collapse again into another Big Bang, called the Big Crunch universe. But we don’t know because general relativity is incomplete. If we find a complete theory, we could get answers to these kinds of questions.

I have always thought of the universe as being sort of a cosmic yoyo; expanding and contracting into another singularity followed by another big bang; having done so forever in the past and continuing to do so forever in the future.

https://www.quantamagazine.org/in-mexico-cosmologist-hunts-for-cracks-in-einsteins-gravity-theory-20220223/?utm_source=pocket-newtab

 

Noel

 

Edited February 27, 20224 yr by birdguy

A cyclic universe, as opposed to an ever expanding universe which never contracts, is not a popular theory with physicists. It used to be many decades ago. Now most evidence is for expanding only, and pretty much forever until everything is so far away from each other that the idea of a universe just in some sense becomes meaningless. Forever.

They say gravity is what causes space to expand. Gravity causes particles of mass to attract each other, but gravity can cause space itself to either expand or contract. Space is not a void in other words, but it is a tangible substance. So the physicists say.

https://lweb.cfa.harvard.edu/seuforum/faq.htm

22 hours ago, birdguy said:

have always thought of the universe as being sort of a cosmic

 

1 hour ago, Fielder said:

A cyclic universe, as opposed to an ever expanding universe which never contracts, is not a popular theory with physicists. It used to be many decades ago. Now most evidence is for expanding only, and pretty much forever until everything is so far away from each other that the idea of a universe just in some sense becomes meaningless. Forever.

 

Not exactly. Penrose has his Conformal Cyclic Cosmology.

And if you consider inflation, something we have evidence for, then there's another feasible cyclic universe feasible.

People often think inflation came after the hot big bang. Not true. First was the inflation field, otherwise known as the inflaton field. That scalar field was expanding exponentially. When it stopped expanding all that energy was dumped into the field. Particles were thus created, jostled together and the hot big bang occured.

Now the thing is that the inflaton field could have been infinite and possibly eternal. So if infinite, the big bang would have occured simultaneously across the entire infinite universe in one go, so what we see now in terms of the expansion of the universe is a reduction in tepreture and density, not a change in size.

Now prior to the inflaton field, there may have been some kind of cosmic singularity but we have no idea if that's true or not. Hence why I emphasised HOT big bang.

Now here's the point. If we project forward into the far distant future, knowing that the universe is accelerating in its expansion, all stars and planets, everything, will be gone and we are left once again with an exponentially expanding scalar field.

If that field stops expanding again, energy is dumped into the field and a new hot big bang occurs and we have a new universe.

Don`t worry another large asteroid will wipe out the human race before that according to some.     

well, mathmaticly there are many options of possible scenarios, als long they can be explained or follow mathmatic rules. But on all these "Theories" we schould not forget that they are just "Theories". Actually what can be observed in practical is an ongoing expansion of the unusiverse, where all objects in the observable Universe are moving away from each other. 

If the Big Bang was something like an explosion, i also try to think about a Granade which explodes and ends at least as a "big chill" once all the initial energy is transformed. And that´s what i think will be the desteny of our universe. It´s just chilling out in darkness, coldness , million times bigger in it´s dimensions as today...well...today? What exactly is "Today"?? Having in mind that from the first micrometer on started from our eyepoint we only see the past not even able to ever see really the present. Time, or what we call it is the most weird thing. Especially when it comes to univers dimensions and it´s relations to matter and space. 

I´am really really curious about, what we will find with the new Webb telescope. If we having in mind how dratically new facts could be observed and theories proved in the last 30 years with the Hubble on duty. What do we have to exspect in the next 30 years...?!? Just think yout the surprise of the scientists when hubble provided it´s deep field and ultra deep field pictures with billions of Galaxies. Now we will have the capabiltiy to see to the edge of the Universe or the the edge of tomorrow´s yesterday.

Edited February 28, 20224 yr by BerndB

23 hours ago, birdguy said:

... But we don’t know because general relativity is incomplete. If we find a complete theory, we could get answers to these kinds of questions.

We could get a answer. Whether that answer is correct or not is another matter and would be determined by observations. Furthermore, people try to poke holes into General Relativity all the time. There is an entire formalism that describes systematic deviations from Relativity (https://en.wikipedia.org/wiki/Parameterized_post-Newtonian_formalism). Measuring bounds for the size of PPN parameters has become a sport among observational astronomers 🙂

Generally, physical cosmology is a strange hybrid thing. It is based on the known laws of physics and there are three impressive pieces of evidence that it could be correct: cosmic microwave background radiation (CMBR); the high degree of isotropy of CMBR (it looks the same from all directions within about 0.01%); and the abundance of light chemical elements (Hydrogen and Helium in particular). On the other hand, cosmology does not deal with repeatable observations and is thus, strictly speaking, natural philosophy rather than science.

 

19 minutes ago, martin-w said:

People often think inflation came after the hot big bang. Not true. First was the inflation field, otherwise known as the inflaton field. That scalar field was expanding exponentially. When it stopped expanding all that energy was dumped into the field. Particles were thus created, jostled together and the hot big bang occured.

Cosmic inflation provides an elegant explanation for the isotropy of CMBR. But we have no observational evidence that cosmic inflation actually happened. 

Peter

If the assumption is that matter cannot be created or destroyed, then a cyclic universe (expansion and contraction) may be possible in many billions of years.  There are some out there who think it may have actually occurred at least once before(?)

But it's hard to wrap one's head around such conjecture...

Even though I am not keen on extremely confined spaces, I would still prefer a cyclic universe to an open ended one.

2 hours ago, qqwertzde said:

 But we have no observational evidence that cosmic inflation actually happened. 

 

Yep. 

 

The theory of inflation thus explains why the temperatures and curvatures of different regions are so nearly equal. It also predicts that the total curvature of a space-slice at constant global time is zero. This prediction implies that the total ordinary matter, dark matter and residual vacuum energy in the Universe have to add up to the critical density, and the evidence supports this. More strikingly, inflation allows physicists to calculate the minute differences in temperature of different regions from quantum fluctuations during the inflationary era, and many of these quantitative predictions have been confirmed.

I decided to do a multicoloured thing today. 

 

2 hours ago, G-RFRY said:

Don`t worry another large asteroid will wipe out the human race before that according to some.     

 

Well something will... obviously. 

2 hours ago, BerndB said:

If the Big Bang was something like an explosion,

 

It wasn't. 

 

1 hour ago, overspeed3 said:

If the assumption is that matter cannot be created or destroyed, then a cyclic universe (expansion and contraction) may be possible in many billions of years. 

 

Except that the universe can arise form nothing and not contravene the first law of thermodynamics. If you add up all the energy in the universe it equates to zero. Because gravitational energy can be defined as negative. Thus the first law is not violated. 

We have redefined what nothing acyaklly is of course. 

"People often think inflation came after the hot big bang. Not true." Exactly.

Ours was not a universe created from a infinitesimal sized and very dense mass. The immense universe was here and inflating and then the spark (the bang, the creation). i.e. something was always here.

The Jews reasoned something like that was true and called that infinite something God (the primal force as they said in the middle ages). But they could not even estimate what it was (inestimable) and forbid any image of it which they thought would have been ugly nonsense to try and picture something unknowable.

How big is the something that was always here Fielder?  And where did it come from?

I hold to the singularity big bang theory and an expanding universe from that into that which was always here.

Noel

 

12 hours ago, birdguy said:

How big is the something that was always here Fielder?  And where did it come from?

 

If inflation theory is correct, and the inflation field (inflaton field) existed prior to the hot big bang, it may have been infinite and eternal. 

The other option is come kind of cosmic singularity prior to the inflaton fields existence. 

 

12 hours ago, birdguy said:

hold to the singularity big bang theory and an expanding universe from that into that which was always here.

 

Same thing. 

inflaton field, or cosmic singularity prior.

Expanding Inflaton field

Inflaton field stops expanding.

Reheating/hot big bang. Temperature and density singularity. Not size, size is only relevant in terms of the observable universe. May be infinite beyond the observable universe.

Our expanding and accelerating universe.

In the distant future only a scalar field left with the same properties as the inflaton field remains.

 

I don't know of any scientists that regard as singularity as truly existing. All "singularity" means is that the mathematics breaks down. We don't have the mathematics to describe such a hot dense state. We need a theory of quantum gravity. 

 

 

 

Edited March 1, 20224 yr by martin-w