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Does "Dark Energy" MAKE Space?


mpmcd101

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I was watching a documentary a few weeks ago about Dark Energy. It was saying that Dark Energy could be thought of as a 5th force, created at the time of the big bang, that is weaker than gravity. It is the force responsible for creating space. In the early universe, it was impeded by gravity, not stopped, but much reduced. Now, at the further reaches of the universe where matter is much less densely packed, gravity has a much weaker hold on matter, so much so, that dark energy is now stronger than gravity in those regions, and so is able to create more space at a greater rate than in the regions where gravity is still stronger than dark energy. It is not a "pushing" force, repelling matter, it is creating space, hence the illusion that bodies with matter are being pushed away from each other, and going faster, the further out you go. In reality, the more thinly spread the matter is, the less gravity can influence it, and so dark energy can do a better job of creating space between the matter. You could say that nothing is really expanding. If you fill a balloon with water, the balloon will expand, but the water is not expanding, there is just more of it being added.



Edited by mpmcd101
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In classical general relativity, which is what we are really talking about here, you do not think of space-time as being created, but rather that the way we measure distances between objects changes with time. Dark energy is basically the negative pressure needed to 'stretch space' rather than create space.

Edited by ajb
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Hi ajb,

 

Well, I'm not sure I necessarily believe that classical view. Yes of course it is the mechanism by which we measure the distance between objects and by which we separate the happening of events, but space is not NOTHING. So, if you can say that space is SOMETHING, then that something has to be manufactured no?

 

Besides which, "Dark energy is basically the negative pressure needed to 'stretch space' rather than create space." This doesn't really explain why expansion is happening faster, the further out you go.

 

These are only my thoughts, I can't offer any maths to back them up, but it seemed to me to be a plausible explanation for the increased speed of the expansion. Do we really know enough to say that it is absolutely one way or the other?

 

It makes sense to think of "Dark Energy" as being something that was born at the time of the big bang, or else why would it just suddenly pop into existence? And, given that it was around back then, before there was any matter in the universe is when expansion began, hence gravity had nothing to work on, so dark energy had nothing to stop it creating space, then as matter emerged, it slowed down since gravity, especially in the very early universe, had a huge role to play as all the matter was very close together. Now, when the most distant matter is spread so far apart, dark energy is once again able to overcome gravity and go on creating space.

 

I'm not a scientist, but I am fascinated by all of science, in particular, cosmology. I like to think, and there are many of us who like to think but who cannot substantiate our thoughts with the maths and I just feel it's a shame that since we can't give any proof/maths, then our thoughts are often not even considered. I do of course realise that science IS proof, and without it, it is just speculation, hence my posting here, but do my thoughts have no merit at all?

Edited by mpmcd101
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but space is not NOTHING.

 

What do you base that on?

 

So, if you can say that space is SOMETHING, then that something has to be manufactured no?

 

But in general relativity (the theory which predicts dark energy) space is not "something".

 

Besides which, "Dark energy is basically the negative pressure needed to 'stretch space' rather than create space." This doesn't really explain why expansion is happening faster, the further out you go.

 

Yes it does. That is what "negative pressure" means: an "outward force" which accelerates expansion.

 

It makes sense to think of "Dark Energy" as being something that was born at the time of the big bang, or else why would it just suddenly pop into existence?

 

It didn't pop into existence. The amount of dark energy is proportional to the volume of space so at some point, there is enough to counter the effects of gravity and cause accelerating expansion.

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... and going faster, the further out you go. In reality, the more thinly spread the matter is, the less gravity can influence it, and so dark energy can do a better job of creating space between the matter.

The juxtaposition of your statements make me think you believe space is thinner at distances we see as far away (i.e., 12B light years), which is not the case as I understand it. On the other hand, I may misunderstand your statements.

 

The Cosmic Microwave Background radiation shows the universe is almost homogenous, because the temperature of that radiation is 2.72548±0.00057 K. In other words, the density at 12BLY is about the same as nearby.

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Hi Strange and EdEarl

 

Space is not nothing. What am I basing this on?

http://physics.stackexchange.com/questions/67582/nothing-vs-empty-space

 

 

But in general relativity (the theory which predicts dark energy) space is not "something".

 

Is there really absolutely no chance that this may not be how things really are? As described by Hawking in the above link - "Perhaps space is something, we just cannot grasp exactly what it is." If Hawking is not 100% sure, then are you in a better state of sureness than he?

 

Quote

Besides which, "Dark energy is basically the negative pressure needed to 'stretch space' rather than create space." This doesn't really explain why expansion is happening faster, the further out you go.

"Yes it does. That is what "negative pressure" means: an "outward force" which accelerates expansion."

This is really, more or less what I was saying except that you are asserting that space is somehow stretched, I am saying that it is not stretched, but that more is being made. When you stretch something, it gets thinner. Is space therefore also getting thinner, or is it the same density throughout? If, as EdEarl says, that it is the same density throughout (which I also believe it is), then it cannot really be said to be stretched, instead, there has to be just more of it.

Nobody really KNOWS absolutely what dark energy is. There is no concrete proof about what it does, so it's a little unfair to tell me that you know absolutely that you are right and that I am wrong, don't you think? I may well be wrong, but as we are all just fishing for answers at the moment, all I ask is that mine be considered as being as valid a guess as anyone else's.

Quote

It makes sense to think of "Dark Energy" as being something that was born at the time of the big bang, or else why would it just suddenly pop into existence?

"It didn't pop into existence. The amount of dark energy is proportional to the volume of space so at some point, there is enough to counter the effects of gravity and cause accelerating expansion."

I didn't say it popped into existence, I said it didn't just pop into existence, and the rest is more or less exactly what I said.

EdEarl,

I don't believe that space is thinner at greater distances, I said that the matter within space, is distributed much more sparsely at greater distances.

Edited by mpmcd101
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Is there really absolutely no chance that this may not be how things really are?

 

Two things:

 

1. Science does not deal with how things "really are". That is philosophy.

 

2. It is entriely possible our current theories will be overturned one day. But that will require evidence.

There is no concrete proof about what it does, so it's a little unfair to tell me that you know absolutely that you are right and that I am wrong, don't you think?

 

I don't think anyone said that.

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EdEarl,

 

I don't believe that space is thinner at greater distances, I said that the matter within space, is distributed much more sparsely at greater distances.

Space is expanding everywhere, locally and at a distance, at about the same rate, and matter is distributed evenly throughout space, both locally and at a distance. That's my understanding. Now clusters of galaxies may be gravitationally bound, e.g., Andromeda and the Milky Way that are moving toward each other, which belong to the Laniakea Supercluster.

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Hi Strange,

 

Two things:

 

1. Science does not deal with how things "really are". That is philosophy.

 

2. It is entriely possible our current theories will be overturned one day. But that will require evidence.

 

I don't think anyone said that.

I thought that philosophy asks questions, science tries to find answers.

 

To over turn current theories does indeed require evidence, but first there has to be an idea.

 

And no, you didn't in so many words, tell me I was wrong, but it is obvious that my suggestions were not considered possible.

 

I realise that many serious scientists frequent this forum. I have never pretended to be one of them. I am just an interested laymen.

 

 

Maybe I am taking things too personally, but I wonder if you are perhaps annoyed with me, your answers appear very blunt, if I have offended you, I do apologise.

Hello EdEarl,

 

I did think that the further out you look, the greater the red shift, meaning that the greater the distance an object is from point n, the faster it is receding. I may well have completely misunderstood, but I thought that that meant the rate of expansion is curved over distance.

 

Also the question of the even distribution of matter throughout the universe is confusing. If, the universe is expanding, and doing so faster toward the further reaches, then the matter in it, at those distances, has to be spread more thinly, no? That is to say, if you were to put sand grains on a rubber sheet, then stretch the sheet equally in all directions, the sand would not continue to be spread with the same density as before. There would be greater distances between the grains, than there was before the stretching. Meaning also that the distribution of matter is also curved over distance, at least as far as the rubber sheet is concerned. Is that not the case with the matter in the universe?

Edited by mpmcd101
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Space is merely volume or distance a common mistake is thinking it is some substance. Space time is a geometric distribution of gravities influence upon particles that resides in that volume. This doesn't change even with virtual particles.

 

Nor does this fact change with string theory. When you see terms such as stretching, created, curved etc they are describing geoemetric influences upon particles and their geometric distribution. Not that space itself is a fabric or substance.

The Einstein field equations, GR, and FLRW metric all treat space time as an ideal gas. These equations all conform to the ideal gas laws. So does the cosmological constant and dark energy.

 

 

A lot of pop media articles use those terms but when you study their professional papers they describe the geometry relations with their mathematics.

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Well, I'm not sure I necessarily believe that classical view.

Okay, but you will need something else to replace this view. Provided we are not too near the classical initial singularity of the Universe, then classical gravity will work well. In this context dark energy is another form of non-gravitational 'stuff' that is providing the required negative pressure. No-one really knows what this 'stuff' is, but there are a few models people work with.

 

These are only my thoughts, I can't offer any maths to back them up, but it seemed to me to be a plausible explanation for the increased speed of the expansion.

Without the mathematics any 'explanation' is not really plausible. You need to fit the models with data, and without a model there is nothing to fit.

 

It makes sense to think of "Dark Energy" as being something that was born at the time of the big bang, or else why would it just suddenly pop into existence? And, given that it was around back then, before there was any matter in the universe is when expansion began, hence gravity had nothing to work on, so dark energy had nothing to stop it creating space, then as matter emerged, it slowed down since gravity, especially in the very early universe, had a huge role to play as all the matter was very close together. Now, when the most distant matter is spread so far apart, dark energy is once again able to overcome gravity and go on creating space.

Presumably dark energy has always been a component of the Universe, but at different stages of the evolution of the Universe other things dominated. This could also be tightly linked to phase changes. Maybe others here who know more about the details of cosmology can say more.

 

 

... but do my thoughts have no merit at all?

I don't know. The creating space thing seems awkward to understand in the context of general relativity. Such things maybe more meaningful in quantum theories where space-time could be seen as an emergent phenomena, but then you would need to show how the classical picture fits into this. One is really pushing the limits of understood physics here.

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Maybe I am taking things too personally, but I wonder if you are perhaps annoyed with me, your answers appear very blunt, if I have offended you, I do apologise.

 

Not at all. I have found that people who present their personal opinions as fact, aren't usually interested in learning. If you asked questions, I might be more verbose! (Also, I just don't have much time right now.)

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Hi Strange,

 

Well I'm glad to hear that at least. I wasn't trying to present my personal opinions as fact, I was trying, in my first post, to condense what I understood from the documentary I saw. (I have tried to search for it online, but to no avail. It was I think on You Tube somewhere, and was talking about the 4 forces and suggesting that the 5th may be dark energy). The rest was reaction to comments by others, based on what I understood from said doc. I did say a few times that these are only my thoughts on the subject and that I am only a layman.

 

I am also very willing to learn. I love to learn about all science, but above all, cosmology. I try to read as much as I can and watch documentaries and join forums. I have a Meade 10" Schmit Cassegrain and spent long hours searching the skies. I might add rather cheekily, that in order to learn well, the teacher must impart knowledge in a manner that is engaging, and not one that sounds slightly miffed, and assumes that the student will probably not be interested to learn in the first place. I would not like to be placed in that sort of generalisation.


Hi ajb, mordred, Strange and EdEarl,

 

I think sadly that I may have made a mistake in trying to participate in this forum. I am really interested in cosmology and everything it entails, so it is a shame, but although I love to think about it, I can never give you what you ask for. I did very basic calculus at school, but that was nearly 40 years ago now and I wasn't very good at it then. All I have are ideas, and it would appear that without the maths to back them up, they are somewhat redundant.

 

Thanks anyway for taking the time to read some of them

Edited by mpmcd101
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I think sadly that I may have made a mistake in trying to participate in this forum.

 

I don't think you should think that. This is a good forum for asking about and discussing science. They just have very strict rules about expressing your own personal "theories". When I have time, I will try and get back to some of your questions in more detail....

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Hi mpmcd101

IDK what mpmcd101 means. It's too difficult to remember. I'd call you M, but that was taken by Flemming. How about 101? :)

 

You found a good place to test your understanding, and to learn.

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Asking questions isn't a problem or getting clarification on something you heard in pop media literature.

 

As mentioned personal theories require mathematics, this aspect is normal on any forum, as the only way to see if a model has merit is comparing the mathematics against the existing models. It also helps to show how predictive a model is.

 

We have an excellent body of experts on this forum willing to teach and provide guidance. For those that want to learn it is an excellent site.

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Good afternoon each,

 

I just would like to say that I didn't mean to imply that this was not a good forum. I'm quite sure that it is an excellent place for the discussion of science. The fault was mine, in that I miscalculated the level of expertise, it would be wrong to say "was needed", but perhaps that would be advantageous in order to maintain a meaningful discussion of the subject in this place. I did take into account that I was not able to provide any proof of my own, hence my posting in the "Speculation" section, but even in this, I think I misunderstood. I just wanted to have a little discussion and toss ideas back and forth with people who like to think about the same things as I do. This I think is not really what happens here, at least not for lay people who have no idea about the maths.

 

I would dearly love to be able to do the maths required to form valid theories and believe me, I have tried to learn, but to sit down and read reams and reams of dry exercises..............Yes I realise that you have all done just that lol, but it is a bit beyond me I'm afraid, and that's only to get to master basic calculus. Then, you have to go on to learn and understand each astrophysical term and value, my head hurts LOL.

 

EdEarl, I'm afraid I will disappoint you again by revealing that my name is Mark, and "mpmcd101" has no great mystery. It is just my initials, 101 is taken from Orwell 1984, it suited my dark streak LOL.

 

I do thank you all for your encouragement, and in the future, if I should continue to post here, I will make sure to pose my ideas as questions, although I have to say, the very title of my post was a question, although I suppose I did lay out the main body of my idea, as a statement, presuming that it would be discussed, not as fact, but as a possible alternative view point, just an idea to be talked about...................my bad! LOL

 

If, in fact, as mentioned by Mordred, all science forums have these strict rules regarding the production of proof, then it seems there is nowhere for lay people like myself, to give vent to their thoughts and ideas, just for the fun of it, and to share them with other like minded people who enjoy talking about this sort of thing. I do understand that for real science, proof is everything. But, just for the enjoyment of exercising your mind and wanting to see what others think about your ideas, I think perhaps that this is not the place.

 

Thanks again

 

Mark

Edited by mpmcd101
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Hi Mark,

You aren't the first, nor will you be the last, to pose questions as if they were statements. I believe folks here do not hold it against anyone for doing so (some are also guilty of the same). The main thing is that you use the experience for learning, instead of pontificating about a pet "theory," because we get folks who really know the world is flat (or some such thing) and who cannot or will not understand. Welcome to scienceforums, lurk in the shadows or say something; we don't bite hard enough to make you bleed.

Edited by EdEarl
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Mark said,

"Also the question of the even distribution of matter throughout the universe is confusing. If, the universe is expanding, and doing so faster toward the further reaches, then the matter in it, at those distances, has to be spread more thinly, no? That is to say, if you were to put sand grains on a rubber sheet, then stretch the sheet equally in all directions, the sand would not continue to be spread with the same density as before. There would be greater distances between the grains, than there was before the stretching. Meaning also that the distribution of matter is also curved over distance, at least as far as the rubber sheet is concerned. Is that not the case with the matter in the universe?"

A rubber sheet will stretch evenly all the way across in all directions if pulled evenly in x and y, thus the grains of sand will spread evenly. Try it with a rubber band that you put marks on every 1/2 inch or so. all the marks will become further apart, evenly.

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Thank you Ed, (can I be cheeky and shorten your name for ease)?

 

Well I think I'm still in one piece LOL so no harm done.

 

I don't know why I had it in my head that things are expanding faster, the further away they are. This would have to pre-presume a starting point, in order to measure distance. Distance from where? Over there is a long way away from me, but not to the thing that is next to it. I am not so conceited as to think that I am the centre of the universe LOL. And, in reality, it would make no difference to what I was trying to "ask" ;) Over there, or right next to me or everywhere at once, the same mechanism could still be in play.

 

I think I have it now, that the universe is expanding everywhere at the same speed, regardless of distance. and the faster bit comes into it because it is accelerating (everywhere at once) when previously it was assumed that it should be slowing down. Is that right? Each bit of matter, although still evenly distributed, is accelerating away from every other bit of matter.

 

I am sure, that what this fabled documentary was saying, was that Dark Energy was being thought of (for the purposes of this documentary at least), as the 5th force. Breaking away from what was thought to be a super force that existed at or shortly before the big bang. Using plank time, it split the 1st second after the big bang into several stages, and this super force braking down into:- gravity, the strong and weak nuclear forces, electromagnetic force and dark energy. It did also use the idea that space was being "created" by this 5th force. Maybe this is semantics, and you could substitute the word "stretched", but I did get the impression that they meant that space, was not nothing, and therefore, had to be "created". Having read the Hawking idea that it was not impossible to think of space as "something", then I wondered if this could really be what we are seeing happen?

http://physics.stackexchange.com/questions/67582/nothing-vs-empty-space

Edited by mpmcd101
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The expanding faster the further away you look is an apparent velocity.

 

Your correct that expansion is the same rate everywhere roughly 70 km/s/Mpc. This is regardless of location.

 

Now for the apparent velocity bit. This is a consequence of Hubbles law.

 

Note recessive velocity is an apparent velocity that depends on distance from the observer. It is not a true velocity as none of the galaxies gain inertia from expansion.

 

Hubbles law states the greater the distance the greater the recessive velocity

 

[latex]v_r=H_OD[/latex]

 

these articles will help cover expansion.

 

http://cosmology101.wikidot.com/redshift-and-expansion

http://cosmology101.wikidot.com/universe-geometry

 

 

http://www.phinds.com/balloonanalogy/: A thorough write up on the balloon analogy used to describe expansion

http://tangentspace.info/docs/horizon.pdf:Inflation and the Cosmological Horizon by Brian Powell

http://arxiv.org/abs/1304.4446:"What we have leaned from Observational Cosmology." -A handy write up on observational cosmology in accordance with the LambdaCDM model.

 

The last one is particularly good in covering various misconceptions.

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Ahhhh, there's the rub!

 

I knew I had heard of a faster expansion rate over distance, I just didn't realise that it was an apparent state of/to the observer, and not an actual velocity increase. I did know that the galaxies are not actually gaining inertia from the expansion, hence the ability to apparently break the light speed rule during inflation, just that space is getting stretched/created (still not ready to drop that idea completely LOL), between them, giving the illusion of an increased velocity.

 

That's an awful lot of reading Mordred, but I will wade through it in time lol, thank you.

 

Mark

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