Why Is a Flat Universe Infinite?

[PeroK]

If there was no void then there must have been an obstacle. By void I mean zero dimensions.

Cosmology has progressed enormously in the past 100 years, from Einstein's General Theory of Relativity to observations of an accelerating expansion, to measuring gravitational waves.

There are unanswered questions, most notably whether there is dark matter influencing galaxy rotation curves and what causes the accelerating expansion.

Modern cosmogy does not rely on meeting with your approval. Cosmologists will continue to research and develop the theories we have. That research is not going to stop and be replaced with "ask albie what he thinks".

 

[vanhees71]

Why are you being rude to me? By creating more space time I meant advancing the spacetime outwards.

The most common view of the big bang is of a singularity exploding into nothingness.

The most common view is that a sufficiently coarse-grained picture of the universe can be described as a Friedeman-Lemaitre-Robertson-Walker spacetime, which has necessarily (Penrose/Hawking) singularities, where the theory breaks down, and nothing can be said about what was really going on close to these singularities.

For the rest of this exact solution of the Einstein field equations, which also implies that the "cosmological substrate" is described as some ideal fluid (which is no surprise given the coarse-graining over large spatial areas we are considering), whose "content" is defined by the corresponding equations of state, there's no "nothingness" into which something explodes. The FLRW solution simply describes the spacetime of the entire universe. The choice of the various components of the matter (+em. radiation) can be inferred from observations. The most important ones are the measurement of the angular distribution of the fluctuations of the temperature of the cosmic microwave background radiation and the distance-redshift relation (Hubble-Lemaitre relation) from measurements on supernovae, which an be taken with some conficence as "standard candles". The best-fit result is then what's described as the "history of our universe":

https://en.wikipedia.org/wiki/Physical_cosmology

 

[Dale]

It's not impossible, no, but it's adding complexity to the model in a way that is deliberately undetectable and with no theoretical justification beyond "it could be true".

It is not impossible, but the resulting models violate Occham’s razor and have less predictive power than current models.

 

[PeterDonis]

Why are you being rude to me?

Pointing out that you are wrong is not rude. It's what you should expect here when you make wrong statements. Particularly when you continue to make wrong statements after it should be abundantly clear to you that your understanding of the subject is flawed and multiple people with much better understanding are trying to help you improve it, but you're not listening to them.

By creating more space time I meant advancing the spacetime outwards.

Which is still wrong.

The most common view of the big bang is of a singularity exploding into nothingness.

Wrong. The Big Bang was not a explosion "into" anything.

 

[PeterDonis]

If there was no void then there must have been an obstacle.

Wrong.

By void I mean zero dimensions.

Wrong.

You need to stop making statements based on your flawed understanding and actually take the time to read, digest, and consider the multiple valid responses you have been given in this thread. Otherwise the discussion will just keep going in circles, which is pointless and a waste of everyone's time.

 

[Dale]

You say having an edge is unjustified and unfalsifiable. What does that mean?

Unjustified means that there is no evidence supporting it. Unfalsifiable means that there can never be evidence against it. These are both problematic scientifically speaking. Because of these two issues there is simply no way that a model with an edge would be considered currently

 

[PAllen]

A flat 2-torus is a counterexample to this. Such a manifold can't be embedded in Euclidean 3-space (as an ordinary curved 2-torus can), but that doesn't mean it doesn't exist.

Technical point: A flat torus cannot be smoothly embedded in Euclidean 3-space. It can be $C^1$ embedded.

A simple physical model of such an embedding is to take a paper cylinder, squash it flat, and now connect its ends. No tears or stretches involved, just 'crinkling' that suggest the required non-smoothness of the formal mathematical treatment.

 

[weirdoguy]

The most common view of the big bang is of a singularity exploding into nothingness.

Why are you repeating this nonsensical claim, when people alreade have told you it's wrong? Now THAT is rude, because it seems you are not listening and not here to learn.

 

[albie]

Cosmology has progressed enormously in the past 100 years, from Einstein's General Theory of Relativity to observations of an accelerating expansion, to measuring gravitational waves.

There are unanswered questions, most notably whether there is dark matter influencing galaxy rotation curves and what causes the accelerating expansion.

Modern cosmogy does not rely on meeting with your approval. Cosmologists will continue to research and develop the theories we have. That research is not going to stop and be replaced with "ask albie what he thinks".

>>

Modern cosmogy does not rely on meeting with your approval.

Of course it does. It has to adhere to logic and all your models of the universe do not.

 

[albie]

Why are you repeating this nonsensical claim, when people alreade have told you it's wrong? Now THAT is rude, because it seems you are not listening and not here to learn.

You all are not giving me logical responses and explanations. Is it any wonder I am confused?

 

[albie]

Pointing out that you are wrong is not rude. It's what you should expect here when you make wrong statements. Particularly when you continue to make wrong statements after it should be abundantly clear to you that your understanding of the subject is flawed and multiple people with much better understanding are trying to help you improve it, but you're not listening to them.Which is still wrong.Wrong. The Big Bang was not a explosion "into" anything.

All you do is say "this wrong". This would go a lot quicker if you actually told me why I was wrong.

 

[albie]

Pointing out that you are wrong is not rude. It's what you should expect here when you make wrong statements. Particularly when you continue to make wrong statements after it should be abundantly clear to you that your understanding of the subject is flawed and multiple people with much better understanding are trying to help you improve it, but you're not listening to them.Which is still wrong.Wrong. The Big Bang was not a explosion "into" anything.

Oh so the big bang wasn't an explosion of energy now? You need to go on wiki and put them right. Including all the websites I've looked at all saying just that.

 

[Ibix]

It has to adhere to logic and all your models of the universe do not.

Your problem here is that when you say "logic" you don't mean that at all. All cosmological models are mathematical models and hence are logical models, since maths is a branch of logic. What you actually mean is that the results of the model don't match your common sense. Which is true, and shouldn't really be a surprise. The universe on the large scale is nothing like your everyday experience.

This would go a lot quicker if you actually told me why I was wrong.

He did. Several posts back up the chain Peter said:

You can't "create more spacetime". Spacetime already includes time, so it already includes all of the effects that will happen over time.

If you didn't understand that, try asking for more explanations.

Oh so the big bang wasn't an explosion of energy now?

No it wasn't. I don't think that even makes sense.

You need to go on wiki and put them right. Including all the websites I've looked at all saying just that.

Where exactly on Wikipedia does it say that the Big Bang was an explosion of energy? We can't do anything about every poor source, but we can at least try on Wikipedia.

The Big Bang origin is a singularity, not an explosion.

 

[Dale]

>>

Of course it does. It has to adhere to logic and all your models of the universe do not.

They do adhere to logic because they can be expressed mathematically. What they do not adhere to is your preconceived notions and assumptions.

You all are not giving me logical responses and explanations. Is it any wonder I am confused?

You not accepting an explanation is not the same as us not giving an explanation.

The current models are based on the assumption that the universe at sufficiently large scales is homogenous, isotropic, and simply connected. The logic is as follows:

1) we observe that what we can see of the universe is homogenous, isotropic, and simply connected

2) we assume that we are not at a special location in the universe. (This is often called the Copernican assumption, since Copernicus introduced the idea that the earth is not the center of the universe)

3) that implies that the universe would be observed to be homogenous, isotropic, and simply connected everywhere

4) that further implies that there is no edge because the universe would not be observed to be homogenous and isotropic near an edge

5) that allows three possible shapes: a positively curved finite space, a zero-curvature (flat) infinite space, or a negatively curved infinite space.

6) observations currently are consistent with 0 curvature, implying a flat infinite space.

7) Projecting this model backwards in time leads to a universe that was hotter and denser in the past. It predicts cosmological redshift and the cosmic background radiation, both of which have been observed.

8) Projecting the model further back we eventually reach a state of infinite density, called a singularity. For mathematical reasons the singularity itself is not part of the model.

9) Just after the singularity, the universe is infinite, flat, and very extremely dense. However, we expect that our classical model breaks down at extreme densities. We are not sure exactly where it breaks down, but wherever it does will be substantially later than the singularity. Therefore, the universe (to the best of our current knowledge) was infinite as far back as our model is valid.

If you don’t understand something here then ask specific follow-up questions. Blanket assertions that it is illogical etc. are both incorrect and not productive.

 

[PeterDonis]

All you do is say "this wrong". This would go a lot quicker if you actually told me why I was wrong.

You have already been told, multiple times, why these statements are wrong. Yet you keep making them.

Also, your statement here goes both ways. See below.

You all are not giving me logical responses and explanations.

"Logic" alone is not enough. Logic always starts with premises. What we are saying doesn't seem "logical" to you because you have the wrong premises somewhere. But we can't help you with that because you are not explicitly stating your premises. You are not giving us the explicit reasoning that is telling you that what we are saying is "not logical". You just keep rejecting what we're saying without explaining why.

 

[PeterDonis]

so the big bang wasn't an explosion of energy now?

That's not what I said. I said the big bang wasn't "a singularity exploding into nothingness" (your words). Which is correct.

You need to go on wiki and put them right. Including all the websites I've looked at all saying just that.

First, Wikipedia and pop science articles aren't good sources for learning actual science. You need to look at textbooks and peer-reviewed papers.

Second, even though the word "explosion" is indeed used often in pop science sources to describe the big bang, I'm not aware of any that say "explosion into nothingness". The "into nothingness" part is the real problem. "Explosion" is not exactly wrong, just likely to be misleading. But "into nothingness" is straight up wrong.

 

[physika]

"advancing outward" "expanding"

expanding on "What" ?

better.

Articulating the reasoning/inquire, implies using the concepts correctly, greater precision, less mess, obviously, logic also counts.

 

[mark!]

The flat universe is NOT infinite. It can’t be. If it would never end, it could have never begun (because space = spacetime). Infinity only exists in mathematics, not in the real world.

 

[Bandersnatch]

Space =/= spacetime.

 

[PeroK]

The flat universe is NOT infinite.

If it's flat, it must be infinite.

It can’t be. If it would never end, it could have never begun (because space = spacetime).

That's patently false.

Infinity only exists in mathematics, not in the real world.

You don't know that. Physics is an empirical science. Until the universe is shown to be finite, there remains the possibility that it is infinite.

 

[mark!]

If it's flat, it must be infinite.

That's patently false.

You don't know that. Physics is an empirical science. Until the universe is shown to be finite, there remains the possibility that it is infinite.

Infinity doesn’t make any sense at all. It’s a concept made up by humans. The decimals of pi are infinite, sure, but numbers are made up by us too you know.

Ok but let me get this straight, you assume that if one would travel the universe in a certain direction, you would ALWAYS be travelling, and always observe new stars and matter around you, forever and ever? You can’t be serious.

 

[mark!]

Space =/= spacetime.

So time is something separate/additional to space, is what you’re saying?

 

[PeroK]

Infinity doesn’t make any sense at all.

There's nothing irrational about a spatially infinite universe. It's one of the main possibilities from the general theory of relativity.

Ok but let me get this straight, you assume that if one would travel the universe in a certain direction, you would ALWAYS be travelling, and always observe new stars and matter around you, forever and ever?

That's a possibility and there is no evidence to exclude it.

You can’t be serious.

The possibility of an infinite universe is at the centre of modern cosmology.

 

[PeterDonis]

Infinity doesn’t make any sense at all.

Speak for yourself. The concept of a spatially infinite universe makes perfect sense to the other posters in this thread, not to mention all of the cosmologists working on our models of the universe that have this property.

Ok but let me get this straight, you assume that if one would travel the universe in a certain direction, you would ALWAYS be travelling, and always observe new stars and matter around you, forever and ever?

Yes, that's what happens in a spatially infinite universe.

You can’t be serious.

I strongly suggest that you take the time to learn about our best current model of the universe before posting further. Your posts, and particularly statements like the one just quoted above, are very uninformed and are not adding anything of value to this discussion.

So time is something separate/additional to space, is what you’re saying?

He's saying that "space" is not the same thing as "spacetime". Which is obvious to anyone who understands what those two terms mean.

 

[mark!]

He's saying that "space" is not the same thing as "spacetime". Which is obvious to anyone who understands what those two terms mean.

So what’s the answer to my question, then?

 

[mark!]

That's a possibility.

How?

 

[PeterDonis]

So what’s the answer to my question, then?

The answer is for you to take the time to learn what our best current model of the universe actually says before posting about it further.

How?

That is what learning what our best current model of the universe actually says will tell you.

Not only are you assuming that you’re more knowledgeable than me

I don't have to assume that, since your posts have already given me plenty of evidence.

but also that this additional knowledge is relevant to even think about making an argument with regard to this topic.

Since you don't have the knowledge, how can you possibly refute such a belief if I have it?

But you don’t explain why (or if) that should be the case. I guess I just have to believe you?

No, you have to do what I've already strongly suggested that you do, twice now: learn what our best current model of the universe already says. Everyone else posting in this thread already knows that, and we are not going to hijack this thread to give you a detailed explanation when you can go find it yourself in any cosmology textbook. If you aren't sure which textbook to use, Liddle's Modern Cosmology is one that is often recommended. Or you could even look at, say, Sean Carroll's online lecture notes on GR, which have a chapter on cosmology that describes a spatially flat infinite universe and gives the basic math for it.

With all that said, you have trespassed on this discussion long enough and you are now banned from further posting in this thread. You have also earned a temporary ban from PF due to the warnings you have received. Please take the time to carefully consider the advice you have been given.