The age of the universe thread

Originally posted by lemon lime
But virtual particles supposedly exist whether space exists or not, ....

I bet you cannot provide a scientific reference along those lines. The very definition of virtual particles requires both space and time.
But what was really being discussed in this thread is the question of whether or not the gap between atoms say, must be filled with matter for there to be space in between them.

The real question has to do with the fundamental properties of space. Are there any constants that set scale? The answer is yes. The speed of light sets the scale at one end and the plank distance at the other. Atoms of a given kind are always the same size. Similarly there are constants of time making atomic clocks constant. None of this makes space a substance, but it does mean it has a real scale, and there is a fundamental difference between things moving away from each other through space and space expanding between them.

Originally posted by lemon lime
[b]Virtual particles existed before the big bang?
This is according to one theory of how everything supposedly all came from nothing. I don't necessarily subscribe to this theory, but we seem to have wandered into the weeds here because it doesn't address apathist's question...
What is space other then the m/e within it?
(Such that it can expand and be curved as if it were a substance.)[/b]

Virtual particles represent a way of describing fields of force. If there are virtual particles then there are forces which seems to mean the universe already exists, so I don't see how a theory can account for the creation of the universe using virtual particles.

Regarding apathist's question, Sakharov suggested the possibility that gravity could be an emergent property. This would mean that it could not exist without matter. So there's no reason why not, but the issue has not been resolved and I'm wary of any grand claims based on this. This thread is littered with posts in which the writer hasn't distinguished between the theories we have about the world and the world itself. Claims about the world, at least scientific ones, should be taking their authority either from properly conducted experiments or verified theories not speculative ones.

There's a wikipedia page about emergent gravity: https://en.wikipedia.org/wiki/Induced_gravity

Originally posted by humy
this isn't one of the theories I for one have ever personally heard of and I fail to see why you would assume I might believe such a theory.
I don't even see how this theory can even relate to anything we just previously discussed even if I hypothetically were to believe this theory.

I'm guessing it's the identification of the universe with a vacuum diagram in quantum field theories.

Originally posted by lemon lime
... But virtual particles supposedly exist whether space exists or not,...

What! I somehow missed that comment in your reply to my post before twhitehead responded to it.
Do you keep making all this stuff up as you go along or what?
According to who or what does "virtual particles supposedly exist whether space exists or not" ? -I have never heard of that one! Where do you keep getting these weird ideas from?

so I don't know what virtual particles have to do with apathists question about space..

apathist stated
"..I think there is no such thing as 'empty space' .."
and I replied;
"..I believe that for all practical purposes, 'empty space' could be reasonably defined as a volume of space that, excluding i.e. ignoring virtual particles, contains no (or at least 'very few' ) particles..."
Obviously, one might[i/] define space as being NOT 'empty' by arguing that virtual particles being within it means that, [i]by definition of 'empty', space it NOT empty.

Then, later, you asked;
"What is space other then the m/e within it? "
Were you asking here about whether by the very definition of space (so you are talking about logically possible, NOT to be confused with casually possible ) whether it is possible for space to be truly empty of m/e, in which case the answer would have been 'yes', it can be truly empty of m/e since there is no logical contradiction in it being truly empty of m/e (and whether it is actually empty of m/e i.e. in physical reality is relevant to that question), or are you asking whether it is casually possible (NOT to be confused with logically possible ) , for space to be truly empty of m/e i.e. whether it can be empty of m/e in physical reality according natural law, in which case the answer would depend entirely on how you define 'empty of m/e' in this narrow context;
IF you are asking about the casually possible of it, not to be confused with logically possible;
If you count virtual particles as being m/e in space, the answer is clearly no, you cannot have space empty of m/e because, according to science (thus according to natural law as we currently understand it) virtual particles do in actuality physically exist in space.
If you don't count virtual particles as being m/e in space, and you also don't count zero-point energy as being m/e in space, the answer is apparently probably 'yes', it, according to science, is probably casually possible to have space truly empty of m/e.

Is that clear to you?

Originally posted by humy
What! I somehow missed that comment in your reply to my post before twhitehead responded to it.
Do you keep making all this stuff up as you go along or what?
According to who or what does "virtual particles supposedly exist whether space exists or not" ? -I have never heard of that one! Where do you keep getting these weird ideas from?

[quote] so I don't ...[text shortened]... probably[/i] casually possible to have space truly empty of m/e.

Is that clear to you?

You're overthinking this. I'm asking if space can exist if it is empty of everything... empty of what we know is there, empty of what we may believe or speculate is there... empty of anything and everything. Can space be completely empty and still exist as (measurable) space?

As to virtual particles I did make a mistake, I was thinking of what had been called a (possible) vast sea of quantum energy prior to the big bang event. There were other exotic theories about a false vacuum, or scalar field, or vacuum energy, or something else that may caused some instability in the 'nothingness'.

Originally posted by lemon lime
You're overthinking this. I'm asking if space can exist if it is empty of everything... empty of what we know is there, empty of what we may believe or speculate is there... empty of anything and everything. Can space be completely empty and still exist as (measurable) space?

As to virtual particles I did make a mistake, I was thinking of what had been ...[text shortened]... ield, or vacuum energy, or something else that may caused some instability in the 'nothingness'.

The stuff about false vacua is probably related to inflation rather than creation itself.

Originally posted by twhitehead
I bet you cannot provide a scientific reference along those lines. The very definition of virtual particles requires both space and time.
But what was really being discussed in this thread is the question of whether or not the gap between atoms say, must be filled with matter for there to be space in between them.

The real question has to do with the ...[text shortened]... rence between things moving away from each other through space and space expanding between them.

...there is a fundamental difference between things moving away from each other through space and space expanding between them.

What is the fundamental difference?

Is space expanding of its own accord and pushing everything away, or are things moving away causing more space to appear between them? Or, are both of these actions happening at the same time?
If two people stand back to back and begin walking away in opposite directions, it can be said they are moving away and the space between them is expanding... it's not either/or, but rather both of these things are happening. The only fundamental difference here is that one of the actions is the cause of the other.

Originally posted by lemon lime
...there is a fundamental difference between things moving away from each other through space and space expanding between them.

What is the fundamental difference? ...

I'm pretty sure that 'fundamental difference' that tw and I think humy see is exactly my confusion about the two analogies (that space expands and can curve) and it comes from the idea of the big bang where our universe begins with all space/time and all matter/energy condensed in a point that goes boom.

Think of galaxies as dots on a balloon that is being expanded or raisins in a cake that is being baked. As opposed to say two people walking away from each other. The dots or the raisins separate from each other not because of some intrinsic velocity difference between them but because the medium in which they are embedded is expanding!

That must be a lousy explanation, sorry. I can see that even if the medium in which they are embedded is expanding, the dots/raisins still have that velocity difference between them. There's a reason or reasons why science says that instead of just a velocity difference between them it must be space itself expanding, I've been exposed to those reasons, but apparently I don't quite get it.

My simple ignorant question is just if space is expanding then obviously space is something as opposed to nothing so what is empty space made of? and then that question looks stupid. The emperor has no clothes.

Originally posted by apathist
I'm pretty sure that 'fundamental difference' that tw and I think humy see is exactly my confusion about the two analogies (that space expands and can curve) and it comes from the idea of the big bang where our universe begins with all space/time and all matter/energy condensed in a point that goes boom.

Think of galaxies as dots on a balloon that is be ...[text shortened]... so what is empty space made of? and then that question looks stupid. The emperor has no clothes.

The idea that space can curve is imo misleading. Gravity will cause objects to follow a curved path, but this doesn't mean space itself is curved. If I'm wrong, and empty space can be curved, then I'm obviously missing something.

Something coming from nothing and (literally) bending empty space is beyond my ability to comprehend.

Originally posted by lemon lime
Can space be completely empty and still exist as (measurable) space?

Clearly yes;
For example, you can pass a light photon through it and measure how long the photon takes to reach the other side and, given c is constant, thus measure the length of that empty space. And if you argue that it is no longer empty as soon as you start passing the photon through it, you can use the workaround of passing the photon not directly though it but rather pass it through some space adjacent i.e. along side it and measure its length that way indirectly.

Originally posted by lemon lime
Gravity will cause objects to follow a curved path, but this doesn't mean space itself is curved.

That isn't where the idea of 'curved space' came from. You must think all these scientists are really stupid.

Originally posted by lemon lime
[b]...there is a fundamental difference between things moving away from each other through space and space expanding between them.

What is the fundamental difference?
[/b]

For things to be accelerated to move away from each other, something must push them apart i.e. there must be an external force exerted on them to accelerate them. There is no such force that we know of that can explain why all the most distant galaxies are moving away from us and the explanation is no such force ever existed because it is the space between the objects that expanded. This is why it is always actually technically incorrect to say the big bang was an 'explosion'.

Originally posted by twhitehead
No, actually, you are talking about your perception of reality. The math is closer to reality than your perception of it.

I doubt a clearer proclamation that the map is more real than reality could ever be made.

Originally posted by lemon lime
What is the fundamental difference?

The speed of light for one.
If space is expanding, then objects can move away from each other faster than the speed of light. If space is not expanding, they can't.

Originally posted by lemon lime
Gravity will cause objects to follow a curved path, but this doesn't mean space itself is curved. If I'm wrong, and empty space can be curved, then I'm obviously missing something.

You are wrong and missing something.
If you were to measure the distance across the sun (diameter) and measure the distance around the sun (perimeter) you would find that the perimeter is not pi time diameter. This is because gravity makes space actually compress within the sun.
The whole effect involves time as well, and this can be measured (and has been measured, and is a necessary consideration for GPS).