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MarkE

Edge of the universe split from A centre of mass of the Universe.

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2 hours ago, MarkE said:

My main point remains that the Universe has to have a border or edge somehow. Because if not, then what lies beyond the matter and energy of our Universe?

The question is meaningless, because spacetime is not embedded into any higher dimensional manifold, so there simply is no “beyond”. Asking what is beyond is like asking what is north of the North Pole - it does not make any physical or mathematical sense.

The existence of a boundary can also be ruled out via other, somewhat more technical arguments. First of all, it is not consistent with the laws of gravity - the Einstein equations have solutions that describe point singularities and ring singularities, but not sheet singularities, being singularities that are spread out like a 2D surface. Your hypothetical boundary would need to be of this kind, since it is by definition a region of geodesic incompleteness. The other main argument here is that, if there is a boundary in all spatial directions, we would essentially have to exist within the interior cavity of an energy-momentum shell of some kind (whether that is massive or not is irrelevant). Now, I do not have a solution to the Einstein equations to hand that describes a dust-filled cavity, but just by briefly thinking about it, and bearing in mind that spacetime in a vacuum cavity is everywhere Minkowski, I can pretty much guarantee that such a spacetime would be very different from the FLRW spacetime which we actually observe around us. In fact, given that ordinary matter density is actually very small over vast distances, I think such a spacetime could reasonably well be modelled by a linearly perturbed Minkowski metric - which is not what we observe. In other words, the FLRW metric that is the best fit for all the experimental data is simply incompatible with the notion of any kind of boundary.

And these are only two arguments that immediately come to mind, I could probably come up with many more if I thought about this hard enough. 

Edited by Markus Hanke

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3 hours ago, MarkE said:

My main point remains that the Universe has to have a border or edge somehow. Because if not, then what lies beyond the matter and energy of our Universe?

That's the wrong way round, surely. If it had a boundary or an edge, then one could ask what is beyond that edge, ie. outside the universe.

But because there is no edge, the question is not necessary; there is no "outside" or "beyond" to ask about.

1 hour ago, MarkE said:

We already know that the first statement is true, the Universe started about 14 billion years ago.

We don't know that. There is no evidence the universe started. We project back, using a theory we know no longer applies, to a notional "time 0"; but there is nothing tat say the universe was created then. 

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4 hours ago, MarkE said:

My main point remains that the Universe has to have a border or edge somehow. Because if not, then what lies beyond the matter and energy of our Universe?

 

I am fond of saying that Nature is stranger than Science.

So I don't see why there has to be an edge if our best Science can come up with examples/theory of 'no-edges'.

The Poincare Disk is one, but that is purely theoretical.

Nature goes one better with a real world example.

Temperature.

What is beyond absolute zero of temperature?

Well we know that, just like the Poincare disk, the closer you approach, the harder it gets to cool the next increment and it is thought impossible to actually reach AZ.

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1 hour ago, studiot said:

 

I am fond of saying that Nature is stranger than our current Science.

There, I fixed it for you :) 

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11 hours ago, MarkE said:

 You're mentioning the CMBR, but this a smal anisotropy, suggesting that galaxies are indeed attracted to the edge of the Universe equally in all directions, exactly what you would expect if the gravitational attraction of an edge behaves like a black hole.

 

I really have no idea how you an believe a that expansion caused by a WH or BH will be uniform. How can you possibly think this is even possible when the strength of the gravitatonal force is stronger as you approach a BH. So how can you possibly claim it will be homogeneous and isotropic as you approach the source mass. Gravity loses strength by a 1/r^2 relation. Take any significant mass,  Plot this at various distances then look at the curve of the gravitational potential as the distance increases. That region will not be homogeneous and isotropic.

 

Edited by Mordred

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15 hours ago, MarkE said:

We already know that the first statement is true, the Universe started about 14 billion years ago. Therefore the second statement can't be true. Do you agree?

No. 2 Points:

  • We do not know that the universe started 13.8 billion years ago. We only know that our theories break down at that point in time.
  • What we do know is supported by observation, and not based on reasoning alone.

Then, just citing Markus:

14 hours ago, Markus Hanke said:

The question is meaningless, because spacetime is not embedded into any higher dimensional manifold, so there simply is no “beyond”. Asking what is beyond is like asking what is north of the North Pole - it does not make any physical or mathematical sense.

I would say this differently:

12 hours ago, studiot said:

I am fond of saying that Nature is stranger than Science.

Nature is even stranger than we can imagine.

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On 6/27/2018 at 2:45 PM, swansont said:

Why would expect that? If there is an edge, why would you be equally attracted to one that is close to you as to one that is very far away?

No I’m saying the exact opposite, if you’re closer to it, you’ll be attracted more strongly, which could explain dark energy (just like a gravitational field of a BH is much stronger when you’re closer to it). 

On 6/27/2018 at 2:45 PM, swansont said:

Why not? I can look at the infinity of numbers between 1 and 2, and then expand my scope and look at the numbers between 1 and 3

Numbers aren’t real, I’ve said that already in another topic. Numbers are invented by humans. Proportions are real (like the Fibonacci sequence), not numbers. You can’t describe reality using only maths. Maths isn’t science, it’s a tool for science.

On 6/27/2018 at 2:45 PM, swansont said:

Why is it reasonable to think there is something "outside" of the universe?

Again, it’s the exact opposite. I don’t think there’s “something” beyond the Universe (because when I’m talking about this term “something” I’m referring to matter or energy, Standard Model stuff), but even the absence of both matter or energy, “nothing” may still exert a gravitational force instead of being inert. We’ve also had this discussion (why a black hole’s gravity can’t be caused by mass of Standard Model matter), so let’s not discuss that again. My point is that, what resides inside a black hole might be of the same nature as this black edge.

22 hours ago, Markus Hanke said:

The question is meaningless, because spacetime is not embedded into any higher dimensional manifold, so there simply is no “beyond”. Asking what is beyond is like asking what is north of the North Pole - it does not make any physical or mathematical sense.

Does it make mathematical sense that there is something rather then nothing? Zero should remain zero (and no mathematical equation will ever change a 0 into a 1), so scientifically speaking, we can’t have a Universe filled with energy in the first place (since you always need a source of energy to create anything). Therefore we’re forced to think beyond mainstream physics, and therefore, even though you’re absolutely right by making that statement, I’m not limiting myself by the notion that it doesn't make physical or mathematical sense.

22 hours ago, Markus Hanke said:

First of all, it is not consistent with the laws of gravity - the Einstein equations have solutions that describe point singularities and ring singularities, but not sheet singularities, being singularities that are spread out like a 2D surface. Your hypothetical boundary would need to be of this kind, since it is by definition a region of geodesic incompleteness

You’re referring to the Einstein equations, but quantum physics is true only for the quantum world, Newtonian physics is true only for our everyday lives on Earth, and Einsteins GR is true on even larger scales. But all three have their limitations, so it’s quite possible that Einstein’s GR has it’s limitations as well on even larger scales, for instance when describing the behaviour of dark energy. So to refer to Einstein equations on one scale/level, in order to rule out my statement about another level, is like referring Newtonian physics when trying to explain something like the strong force. Again, you’re absolutely right, the law is correct, but on different levels there seem to be different laws, and dark energy might be part of such a different level.

This boundary/edge is not a thing, not made of stuff, but it’s a region that might be described with the same behaviour as a black hole. So indeed, there’s nothing (not "something", meaning no matter/energy) beyond the Universe, but that doesn’t mean it’s inert towards matter/energy. In fact, it might be the most attractive force of all. Perhaps it could even describe dark energy without the need of anything new/exotic.

20 hours ago, studiot said:

So I don't see why there has to be an edge if our best Science can come up with examples/theory of 'no-edges'

To explain dark energy without adding a new form of energy. And to explain how a Universe could have come from nothing.

15 hours ago, Mordred said:

I really have no idea how you an believe a that expansion caused by a WH or BH will be uniform. How can you possibly think this is even possible when the strength of the gravitatonal force is stronger as you approach a BH. So how can you possibly claim it will be homogeneous and isotropic as you approach the source mass. Gravity loses strength by a 1/r^2 relation. Take any significant mass,  Plot this at various distances then look at the curve of the gravitational potential as the distance increases. That region will not be homogeneous and isotropic.

I really think we’re not talking about the same thing here. You have way more expertise, so I wouldn’t dare to question these kinds of insights of yours. I just think we’re not talking about the same thing here (probably because I’m not explaining it at your level of understanding). Sorry, I'm trying my best!

Edited by MarkE

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5 minutes ago, MarkE said:

To explain dark energy without adding a new form of energy. And to explain how a Universe could have come from nothing.

I thought we were talking about the Universe as we see it today, not where it came from or where might be going.

As to dark energy, that wasn't in the OP. It was stated to be about expansion.

I said nothing whatsoever about a new form of energy.

 

I was simply trying to get you to think about/work through the implications of what you were proposing.
If you are going to move the world cup posts, I'm out of here.

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15 minutes ago, MarkE said:

Does it make mathematical sense that there is something rather then nothing?

Sorry, but I do not see the connection to the question of whether or not the universe has a boundary.

15 minutes ago, MarkE said:

This boundary/edge is not a thing, not made of stuff, but it’s a region that might be described with the same behaviour as a black hole

If this were the case, this region would need to be behind an event horizon. The process of anything falling through such a horizon is not unitary - meaning it‘s not a reversible process. Due to Landauer‘s principle, this would imply that this horizon radiates heat, so actually the universe would have to be really, really hot, and continuously heating up further. This is not what we observe.

Also, even if you say that GR is not valid for the boundary itself, it would have to be valid for the event horizon, since that is a region of smooth and regular spacetime at some distance from your boundary. And again, I do not think that an event horizon with the global topology and geometry of a flat sheet is compatible with GR.

15 minutes ago, MarkE said:

In fact, it might be the most attractive force of all.

If that were true, then all force vectors would cancel out, leaving zero net force, so there would be no relative motion of galaxies at all. Again, this is not what we observe.

Edited by Markus Hanke

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54 minutes ago, MarkE said:

No I’m saying the exact opposite, if you’re closer to it, you’ll be attracted more strongly, which could explain dark energy (just like a gravitational field of a BH is much stronger when you’re closer to it). 

That's not the opposite of what I said.

And it's not what you said earlier: "galaxies are indeed attracted to the edge of the Universe equally in all directions"

54 minutes ago, MarkE said:

 

Numbers aren’t real, I’ve said that already in another topic. Numbers are invented by humans. Proportions are real (like the Fibonacci sequence), not numbers. You can’t describe reality using only maths. Maths isn’t science, it’s a tool for science.

Science doesn't describe reality. It describes behavior, and yes, you can use maths for that. You must use maths for quantifiable behavior. How strongly something is attracted to another is an example of quantifiable behavior.

What does this have to do with your absurd claim that something that is infinite can't be expanding?

54 minutes ago, MarkE said:

Again, it’s the exact opposite. I don’t think there’s “something” beyond the Universe (because when I’m talking about this term “something” I’m referring to matter or energy, Standard Model stuff), but even the absence of both matter or energy, “nothing” may still exert a gravitational force instead of being inert. We’ve also had this discussion (why a black hole’s gravity can’t be caused by mass of Standard Model matter), so let’s not discuss that again. My point is that, what resides inside a black hole might be of the same nature as this black edge.

I will rephrase. Why is it reasonable to think there is a border to the universe?

Also, "we had this discussion" does not mean that your assertions can be taken as being correct. 

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2 hours ago, MarkE said:

No I’m saying the exact opposite, if you’re closer to it, you’ll be attracted more strongly, which could explain dark energy (just like a gravitational field of a BH is much stronger when you’re closer to it). 

Gravity doesn't work like that: https://en.wikipedia.org/wiki/Shell_theorem

 

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20 hours ago, Markus Hanke said:

If this were the case, this region would need to be behind an event horizon. The process of anything falling through such a horizon is not unitary - meaning it‘s not a reversible process. Due to Landauer‘s principle, this would imply that this horizon radiates heat, so actually the universe would have to be really, really hot, and continuously heating up further. This is not what we observe.

You’re saying that this hypothetical boundary/edge would be behind an event horizon (just like a BH). The process of anything falling through such a horizon is not a reversible process, and that it should radiate heat (just like Hawking radiation). Therefore “the universe would have to be really, really hot, and continuously heating up further”. Is that the right conclusion to make? If I understand you correctly, what you’re concluding is that this lost energy has to be accounted for. Well, why do cosmologists never take living organisms in account? We’re definitely adding something to the Universe, since we are changing our composition (evolving) and thus become more organised, and apply more order (reverse entropy), and according to some interpretations of quantum mechanics it's nonlocal, meaning the quantum state of each particle cannot be described independently of the state of others, even when the particles are separated by a large distance. A quantum state must be described for the system as a whole. In the case of consciousness, David Bohm pointed toward evidence presented by Karl Pribram that memories may be enfolded within every region of the brain rather than being localised (for example in particular regions of the brain, cells, or atoms). So how do we, living organisms, fit in? Why would you conclude "this is not what we observe", and thereby ignore yourself when describing the workings of the Universe? 

20 hours ago, Markus Hanke said:

If that were true, then all force vectors would cancel out, leaving zero net force, so there would be no relative motion of galaxies at al

Could you explain a bit further please why this would be the case? 

19 hours ago, swansont said:

And it's not what you said earlier: "galaxies are indeed attracted to the edge of the Universe equally in all directions"

That's not my quote, this was my quote:

On 6/27/2018 at 2:27 PM, MarkE said:

@Mordred You're mentioning the CMBR, but this a smal anisotropy, suggesting that galaxies are indeed attracted to the edge of the Universe equally in all directions, exactly what you would expect if the gravitational attraction of an edge behaves like a black hole.

What we do observe is that galaxies that at twice as far away from us have redshifts that are also twice as large. Does this mean that the Hubble distance will increase forever, without any limit?

19 hours ago, swansont said:

Science doesn't describe reality. It describes behavior, and yes, you can use maths for that. You must use maths for quantifiable behavior. How strongly something is attracted to another is an example of quantifiable behavior.

Do we really have to use maths to describe how strongly something is attracted by something else? Also on Earth? You can't explain observations of movements of particles just by maths alone. Where is the force that lifts your finger to type the words on your keyboard coming from? That's also an attractive force, isn't it? We're not objects following simple rules of attraction set by the laws of nature that we've discovered. Not that those laws are wrong, but being human is very different from inorganic matter. So if you were referring only to inorganic matter, than you're absolutely right, but I really think you're thinking too mechanical and scientifically about humans.

19 hours ago, swansont said:

What does this have to do with your absurd claim that something that is infinite can't be expanding?

It depends on what your definition of "infinite" means. What does an infinite Universe mean in the first place? How is it infinite? Were you referring to the mathematical definition of "infinite"? 

19 hours ago, swansont said:

I will rephrase. Why is it reasonable to think there is a border to the universe?

Because I'm a supporter of the notion that the Universe came from nothing, since I don't believe in free energy, which has always existed, and without any input was already present. And because of that, you'd expect to find that initial state at the far end of the Universe (meaning the beginning of the Universe). Why do living organisms die? Because no matter how you handle or conserve the energy that you possess, you will eventually return to that initial state. On another level, that same rule applies in a physical sense, because all energy will also, quite literally, return to where it came from, if no force is acted upon it (by living organisms). A static Universe therefore can’t be right (and has been ruled out) because that would mean free energy. But a Universe with energy not being attracted back, to disappear into mass, would also mean a Universe with free energy, and if there’s one thing I don’t believe, it’s free energy. So in some way, all living things are kind of “virtual” (referring to how virtual particles behave) since we exist for a small period of time, and then die, but before that, we’re able to reproduce ourselves to postpone our fate.

18 hours ago, Strange said:

Gravity doesn't work like that: https://en.wikipedia.org/wiki/Shell_theorem

The event horizon is a stronger gravitational part of a black hole, so gravity could be much stronger on short distances (not 4πr2 (3 dimensions), like the inverse square law of light, but 2πr (2 dimensions). Compared to the other three forces, the force of gravity gets much stronger at smaller distance scales and higher energies. I'm not sure if that pattern continues all the way down (since quantum gravity hasn't been figured out yet), but the force of gravity should overwhelm the other forces at that scale.

Edited by MarkE

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48 minutes ago, MarkE said:

The event horizon is a stronger gravitational part of a black hole, so gravity could be much stronger on short distances (not 4πr2 (3 dimensions), like the inverse square law of light, but 2πr (2 dimensions). Compared to the other three forces, the force of gravity gets much stronger at smaller distance scales and higher energies. I'm not sure if that pattern continues all the way down (since quantum gravity hasn't been figured out yet), but the force of gravity should overwhelm the other forces at that scale.

So you are proposing a modification to the law of gravity to get round the shell theorem (I would like to see the mathematical proof that changing from a square law does, in fact do this).

But we see no evidence for gravity working this way.And if it only occurs very close to an even horizon (so we cannot, yet, observe it) how is it able to affect the speeds of galaxies across the entire universe.

I have another, more philosophical, problem with your idea. If dark energy is due to some kind of event horizon surrounding the observable universe, that puts using he exact centre of the universe. This raises all sorts of awkward questions.

 

54 minutes ago, MarkE said:

What we do observe is that galaxies that at twice as far away from us have redshifts that are also twice as large.

You do realise that this is just a consequence of simple arithmetic? 

Quote

Does this mean that the Hubble distance will increase forever, without any limit?

As expansion is accelerating, the Hubble constant(*) is increasing and so the Hubble distance (speed of light / Hubble constant) is decreasing.

(*) not really a constant

58 minutes ago, MarkE said:

Do we really have to use maths to describe how strongly something is attracted by something else?

Of course. "Strongly" is a quantitative thing and therefore requires maths.

59 minutes ago, MarkE said:

You can't explain observations of movements of particles just by maths alone.

You can' explain them at all without maths.

 

1 hour ago, MarkE said:

It depends on what your definition of "infinite" means. What does an infinite Universe mean in the first place? How is it infinite? Were you referring to the mathematical definition of "infinite"? 

An infinite universe means one without end; however far you go, you can always go further. The is exactly analogous to the mathematical definition (however large a number you get to, there is always a successor).

1 hour ago, MarkE said:

Where is the force that lifts your finger to type the words on your keyboard coming from?

Muscles.

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1 hour ago, MarkE said:

 That's not my quote, this was my quote:

Um, that's the same quote. I just trimmed the irrelevant parts.

 

1 hour ago, MarkE said:

What we do observe is that galaxies that at twice as far away from us have redshifts that are also twice as large. Does this mean that the Hubble distance will increase forever, without any limit?

How about addressing my objection, instead of going off on a tangent? 

1 hour ago, MarkE said:

Do we really have to use maths to describe how strongly something is attracted by something else? Also on Earth?

Yes, we do.

Can you tell me how strongly a 100 kg object will be attracted to earth without using maths?

1 hour ago, MarkE said:

You can't explain observations of movements of particles just by maths alone. Where is the force that lifts your finger to type the words on your keyboard coming from?

You have changed the conditions by adding "explain observations" and asking where a force comes from is not an example of a quantifiable behavior. You are addressing something other than what I was claiming.

1 hour ago, MarkE said:

That's also an attractive force, isn't it? We're not objects following simple rules of attraction set by the laws of nature that we've discovered. Not that those laws are wrong, but being human is very different from inorganic matter. So if you were referring only to inorganic matter, than you're absolutely right, but I really think you're thinking too mechanical and scientifically about humans.

You will fall in a vacuum at a different rate than a rock? The orbit of the ISS is different than the astronauts that inhabit it? Do tell.

1 hour ago, MarkE said:

It depends on what your definition of "infinite" means. What does an infinite Universe mean in the first place? How is it infinite? Were you referring to the mathematical definition of "infinite"? 

If you are using some special definition, you need to say so. This is your claim, not mine.

1 hour ago, MarkE said:

Because I'm a supporter of the notion that the Universe came from nothing, since I don't believe in free energy, which has always existed, and without any input was already present. And because of that, you'd expect to find that initial state at the far end of the Universe (meaning the beginning of the Universe).

So no actual physics

1 hour ago, MarkE said:

Why do living organisms die? Because no matter how you handle or conserve the energy that you possess, you will eventually return to that initial state.

I think you need to study up on thermodynamics.

1 hour ago, MarkE said:

On another level, that same rule applies in a physical sense, because all energy will also, quite literally, return to where it came from, if no force is acted upon it (by living organisms). A static Universe therefore can’t be right (and has been ruled out) because that would mean free energy. But a Universe with energy not being attracted back, to disappear into mass, would also mean a Universe with free energy, and if there’s one thing I don’t believe, it’s free energy. So in some way, all living things are kind of “virtual” (referring to how virtual particles behave) since we exist for a small period of time, and then die, but before that, we’re able to reproduce ourselves to postpone our fate.

 

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Mark it sounds like your trying to avoid acceptance by ignoring the physics. This won't work. For example the Universe from nothing model is often described as the ultimate free lunch. It is also a model which supports the LCDM model in terms of expansion. There is no conflict between the two models in terms of Hubbles limit etc.

 No one is arguing against the viability of the Universe from model in this thread. However keep in mind that model requires flat curvature and must approximate the non linear terms of curvature and uses pseudo tensors, however that isn't the topic of this thread.

Yes the universe can expand without limit, however eventually our observable portion will reach a limit. At some point light will not be able to overcome the rate of expansion but this is a few Billion years into the future.

Living organisms will not affect expansion. Have you ever looked at just how big the universe is ? How can you possibly think the movement of the population of Earth or even every possible habitable planet will affect such vast distances. That is a conjecture with absolutely no basis.

The loss of strength of gravity is a consequence of a central force potential in a volume. It already takes into account the formulas for the volume you mentioned.

Here is the entire problem with your idea of a BH cause to the DE component. Expansion occurs in all directions equally it is not directional ie outward. That is an anistropic directional component which expansion is not. If expansion was directional ie outward then we would measure this directional component via the changes of ANGLES BETWEEN GALAXIES

An outward motion would cause those angles to change, this is not what is measured instead all angles are preserved.

By the way the Universe from nothing model says nothing about the universe being part of a BH, in point of detail those two ideas conflict with one another. They would be incompatible models. However you would have to see the maths to understand that.

 

Edited by Mordred

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3 hours ago, MarkE said:

Is that the right conclusion to make?

I think it is, because in the scenario you suggest the universe does not expand, so the heat has nowhere to dissipate to. It‘s somewhat like a pressure cooker that is powered from its own interior, until there is no information left to be destroyed.

I can‘t comment on the rest of that paragraph since it does not seem to be connected to the topic at hand.

3 hours ago, MarkE said:

Could you explain a bit further please why this would be the case? 

Because it would essentially be the same scenario as the interior of a shell (even if the shell itself is not thought of as massive) - and we know that this yields a region with uniform gravity, both in Newton as well as in GR. Hence no net gravitational attraction to the boundary anywhere. This alone renders the whole concept inconsistent.

3 hours ago, MarkE said:

How is it infinite?

I believe he means infinite in the sense that geodesics can be extended indefinitely without ever terminating anywhere, or connecting back on themselves.

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I’d like to visualise what I’m talking about.

First there's the observable Universe, which is where we are. Next, it's possible that even more galaxies lie beyond the observable Universe (and perhaps even more Universes in one giant multiverse). Note that this belt is obviously not to scale, because we don’t know how far this region stretches.

hgAeEnF.jpg

My question is: what do we find at the region of the question mark (meaning beyond the boundary of (all) Universe(s))? 

A) If your answer is “On the question mark we'll find even more galaxies” then my question is "What lies beyond them?". There has to be a last galaxy, or at least a last particle, because the Universe contains an amount of particles, instead of an infinite uncountable quantity, because that doesn’t make any real sense (only in mathematics).

B) If your answer is “On the question mark we'll find nothing at all”, then what can you tell me about these last galaxies/particles at the far end of the belt with more galaxies (the boundary before the question mark)? How do these particles inwards/outwards behave?

C) If your answer is neither A or B, then what could be an alternative explanation?

 

If all of this has nothing at all to do with dark energy whatsoever (which is why this topic was started in the first place), my question is: What do you think is the most plausible explanation for dark energy? 

Bonus points to anyone who attempts to visualise his explanation as well ;).

Edited by MarkE

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Just now, MarkE said:

My question is: what do we find at the region of the question mark (meaning beyond the boundary of (all) Universe(s))? 

Either the universe is infinite (answer A) or it is finite bout unbounded (answer C). I am not aware of anything that could support answer B; it would require some sort of barrier to stop the matter in the universe filling that "void".

4 minutes ago, MarkE said:

If all of this has nothing at all to do with dark energy whatsoever

It is hard to see how it could do (even if your outer region were full of super-dense neutronium). Because, as noted, gravity doesn't work that way. But also because (unless I am very confused, which is entirely possible!) the rate of expansion is less at greater distance from us. The acceleration started relatively recently so it is nearer (later) galaxies that show an increased expansion rate.

2 minutes ago, MarkE said:

What do you think is the most plausible explanation for dark energy? 

It appears to be a constant, non-zero energy density  present in otherwise empty space. The challenge is how this relates (if it does) to the known non-zero energy of the vacuum (which appears to be many orders of magnitude too large).

 

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6 minutes ago, Strange said:

Either the universe is infinite (answer A) or it is finite bout unbounded (answer C). I am not aware of anything that could support answer B; it would require some sort of barrier to stop the matter in the universe filling that "void".

It is hard to see how it could do (even if your outer region were full of super-dense neutronium). Because, as noted, gravity doesn't work that way. But also because (unless I am very confused, which is entirely possible!) the rate of expansion is less at greater distance from us. The acceleration started relatively recently so it is nearer (later) galaxies that show an increased expansion rate.

It appears to be a constant, non-zero energy density  present in otherwise empty space. The challenge is how this relates (if it does) to the known non-zero energy of the vacuum (which appears to be many orders of magnitude too large).

 

Thanks! Interesting thoughts.
If answer A is indeed more plausible than answer B, I think I'll have to rearrange my brain a little bit. That's going to be a tough job, but I'll try.

Edited by MarkE

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19 minutes ago, MarkE said:

I think I'll have to rearrange my brain a little bit. That's going to be a tough job, but I'll try.

No one said it was going to be easy! ^_^

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28 minutes ago, Strange said:

I am not aware of anything that could support answer B; it would require some sort of barrier to stop the matter in the universe filling that "void".

Does there have to be a void? Cant'the 'edge'  be the same as in an infinite universe, i.e. none, and it doesn't need to have an edge since the expanding space is created within the universe itself. Lots of loose ends there btw. My thinking: volume is a function of space and the volume of space with no occupants is zero, so, there is zero space around a finite universe. The point I'm trying to get to is there is no 'wall'... it's just absence of anything.

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On 7/1/2018 at 1:24 PM, StringJunky said:

Cant'the 'edge'  be the same as in an infinite universe, i.e. none, and it doesn't need to have an edge since the expanding space is created within the universe itself. Lots of loose ends there btw. My thinking: volume is a function of space and the volume of space with no occupants is zero, so, there is zero space around a finite universe. The point I'm trying to get to is there is no 'wall'... it's just absence of anything.

A clear understanding of what space is, is required to answer the question, I do not think one exists.

space time includes ER / EPR bridges which have wormholes around space time. Inside a wormhole distance/volume are not an issue.  

Could an absence of spacial volume be regarded as the inside of a wormhole, or another dimension where space and or time is not required. 

Could the universe exist inside a wormhole or another none spacial dimension. ?

As a kind of superposition thereom could we exist inside a wormhole which exists as a result of a MECO BH / WH interaction.

 

 

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41 minutes ago, interested said:

A clear understanding of what space is, is required to answer the question, I do not think one exists.

It does. It just doesn't seem to have ever sunk into your head. Which is why you keep making the same baseless assertions over and over again, even after having had countless explanations as to why you are misusing terminology and misunderstand physics.

42 minutes ago, interested said:

space time includes ER / EPR bridges

EPR is a paper about an apparent paradox in quantum theory. It has nothing to do with spacetime in relativity.

43 minutes ago, interested said:

Could an absence of spacial volume be regarded as the inside of a wormhole, or another dimension where space and or time is not required. 

This make no sense.

43 minutes ago, interested said:

As a kind of superposition thereom could we exist inside a wormhole which exists as a result of a MECO BH / WH interaction.

What is a MECO?

What evidence is there that white holes exist?

 

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12 hours ago, interested said:

A clear understanding of what space is, is required to answer the question, I do not think one exists.

Of course we do! Spacetime is observed to be warped, twisted, curved, and forming waves when mass/energy is involved. 

 

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28 minutes ago, beecee said:

forming waves

Forming or foaming?

:)

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