what exists at the edge of our universe?

[mad_scientist]

is it more space...or?

[StringJunky]

If there was more space it wouldn't be the edge, would it? It could be finite and unbounded, or infinite.

[Function]

I sense 7 pages of discussions I understand nothing about incoming. Give or take a few. Within ... a week or 2.

Edited April 4, 2017 by Function

[Country Boy]

Your question assumes the universe has an edge! Can you prove that?

[fred2014]

I would suggest there is some evidence of what might be out there.

Personal opinion follows please correct anything I have wrong:

 

We know that the universe is expanding and that the mass of the universe

is accelerating faster than a closed model (big bang or inflation) predicts.

The only force we have evidence for that can make mass accelerate in

that manner is gravity.

 

To answer the OP's question - my suggestion is that the universe is

a "bubble" surrounded on all sides by other "bubbles" - like froth.

those other bubbles are universes with their own mass and if there are a

large amount of them or even infinite number - that might account for the

increasing acceleration at the edges of our "bubble"

 

This doesn't address the issue with gravity "drop off" at the edges of galaxies

but I don't see why that shouldn't be a totally different phenomena.

(You can glean I'm not at all convinced about all the "dark" suggestions

nor do I see any reason why we should imagine our universe is all there is

just because we can't "see" any further. Calculating the mass of a universe

based on what we can see, seems like a pretty dodgy exercise to me.)

[Strange]

We know that the universe is expanding and that the mass of the universe

is accelerating faster than a closed model (big bang or inflation) predicts.

 

 

Not with the addition of a cosmological constant ("dark energy").

 

 

 

The only force we have evidence for that can make mass accelerate in

that manner is gravity.

 

To answer the OP's question - my suggestion is that the universe is

a "bubble" surrounded on all sides by other "bubbles" - like froth.

those other bubbles are universes with their own mass and if there are a

large amount of them or even infinite number - that might account for the

increasing acceleration at the edges of our "bubble"

 

Doesn't work. See Newton's shell theorem.

 

 

You can glean I'm not at all convinced about all the "dark" suggestions

nor do I see any reason why we should imagine our universe is all there is

 

These seem contradictory. The whole point of dark matter is that there is more to the universe than we can see.

 

 

nor do I see any reason why we should imagine our universe is all there is

just because we can't "see" any further.

 

Nobody thinks that. We are pretty certain that the universe is much larger than we can see, if not infinite.

 

 

Calculating the mass of a universe

based on what we can see, seems like a pretty dodgy exercise to me.

 

That would be the mass of the observable universe. The mass of the whole universe is almost certainly much larger than that, if not infinite.

[Pugdaddy]

The TV series Through the Wormhole has an episode on this question.

 

[fred2014]

We know that the universe is expanding and that the mass of the universe

is accelerating faster than a closed model (big bang or inflation) predicts.

 

 

 

Not with the addition of a cosmological constant ("dark energy").

 

 

I agree that the concept of "dark energy" seems to resolve

the maths - but that's because it was designed to. Not because

it was seen to do so.

 

I prefer to think there is something we don't know

about gravity - or the amount of black holes or their behaviour.

Inventing 2 new things before breakfast is fun - but I find

it somewhat suspicious.

 

There seems to be a growing trend of scepticism about dark matter

and dark energy in general. I don't think it's just me.

 

As an asside:

When it comes to dark energy maybe I've missed the explanation

of the "opposite reaction" - what is it pushing against?

Why can't we detect that either? has that even been looked for?

 

Too many questions that have the "impossible to detect" answer for my

liking. (Again - from a laymans perspective)

 

 

 

 

The only force we have evidence for that can make mass accelerate in

that manner is gravity

 

To answer the OP's question - my suggestion is that the universe is

a "bubble" surrounded on all sides by other "bubbles" - like froth.

those other bubbles are universes with their own mass and if there are a

large amount of them or even infinite number - that might account for the

increasing acceleration at the edges of our "bubble".

 

 

 

 

Doesn't work. See Newton's shell theorem.

 

 

 

That sounds pretty definite - thanks for the suggestion I'll check it out.

 

 

 

 

Doesn't work. See Newton's shell theorem.

 

Looking at that I don't see any reason why it should apply.

It seems to reference perfect spheres. I don't think

the universe is a perfect sphere - in fact I seem to remember

something about saddle shapes but don't quote me on that.

 

I think my notion holds up still.

 

 

[Pugdaddy]

Sean Carroll does his best to wave the banner for Dark Energy. In this lecture he gives some compelling observational evidence for DE based on the Bullet Cluster. But, Milgrom's MOND(Modified Newtonian Dynamics) theory works on a smaller scale. Jacob Bekenstein TeVeS(Tensor-Vector-Scalar) is a relativistic generalization of MOND. You be the Judge!!

 

Some links of interest.

http://www.astro.umd.edu/~ssm/mond/

https://en.wikipedia.org/wiki/Tensor%E2%80%93vector%E2%80%93scalar_gravity

[Strange]

I agree that the concept of "dark energy" seems to resolve

the maths - but that's because it was designed to. Not because

it was seen to do so.

 

Dark energy is just a placeholder for whatever turns out to be the explanation. This could some form of energy, it could be a change to the way gravity works, it could be something else.

 

 

There seems to be a growing trend of scepticism about dark matter

and dark energy in general.

 

Citation needed.

 

 

When it comes to dark energy maybe I've missed the explanation

of the "opposite reaction" - what is it pushing against?

 

It isn't pushing against anything. It just changes the energy density of the universe, which changes the rate of expansion. Expansion doesn't happen because things are pushed apart. It would be more accurate to think of them as just drifting apart (because that is the natural thing to do in the absence of force).

 

 

Looking at that I don't see any reason why it should apply.

It seems to reference perfect spheres. I don't think

the universe is a perfect sphere - in fact I seem to remember

something about saddle shapes but don't quote me on that.

 

Expansion (and the acceleration) is isotropic (as far as I know) so it would require an even distribution of external mass pulling on the universe. At which point, it all cancels out as Newton showed.

 

And there is no "outside" of the universe anyway (as far as we know).

Sean Carroll does his best to wave the banner for Dark Energy.

 

Dark matter.

[Pugdaddy]

Right. The Bullet Cluster is evidence for Dark Matter. But I think he believes that all of the Dark Sector(Dark Matter and Dark Energy) is probably true.

[Strange]

Right. The Bullet Cluster is evidence for Dark Matter. But I think he believes that all of the Dark Sector(Dark Matter and Dark Energy) is probably true.

 

 

There are two things here. At one level, both dark matter and dark energy are names for something unknown that causes an observed effect. So in that sense they are both "true".

 

In the case of dark matter, the evidence is now fairly overwhelming that it is some form of matter (or something that behaves very much like some form of matter). However, people are (of course) still looking at alternatives such as modified gravity.

 

And people are looking at a whole range of possible explanations for the effects attributed to "dark energy". Some of these also involve changes to gravity. As far as I know, it is much too early to draw any conclusions.

Edited April 5, 2017 by Strange

[Pugdaddy]

Another interesting area of research is the existence of "chameleon fields”. This was first hypothesized in 2004 by University of Pennsylvania physicist Justin Khoury. Ten years later English physicist Clare Burrage proposed a methodology for testing their existence in a laboratory using atoms. Paul Hamilton of UCLA has conducted experiments to test for these "chameleon fields”, where Dark Energy may live. No smoking gun yet, but they have put restraints/doubts on some of the proposed theories. Also experiments have provided a better understanding of how strongly "chameleon fields" can interact with normal matter. Baby steps.

Edited April 5, 2017 by Pugdaddy

[Delta1212]

 

 

 

I agree that the concept of "dark energy" seems to resolve

the maths - but that's because it was designed to. Not because

it was seen to do so.

 

I prefer to think there is something we don't know

about gravity - or the amount of black holes or their behaviour.

Inventing 2 new things before breakfast is fun - but I find

it somewhat suspicious.

 

There seems to be a growing trend of scepticism about dark matter

and dark energy in general. I don't think it's just me.

 

As an asside:

When it comes to dark energy maybe I've missed the explanation

of the "opposite reaction" - what is it pushing against?

Why can't we detect that either? has that even been looked for?

 

Too many questions that have the "impossible to detect" answer for my

liking. (Again - from a laymans perspective)

 

 

 

 

 

 

 

 

 

 

 

 

That sounds pretty definite - thanks for the suggestion I'll check it out.

 

 

 

 

Looking at that I don't see any reason why it should apply.

It seems to reference perfect spheres. I don't think

the universe is a perfect sphere - in fact I seem to remember

something about saddle shapes but don't quote me on that.

 

I think my notion holds up still.

 

 

Following up on Strange's comment: If expansion were caused by gravity from some mass beyond the observable universe, that mass must completely surround our universe as, as Strange said, expansion is isotopic. However, if the universe were uniformly surrounded by mass in this way, you run into the problem described by She'll theorem, where the gravity from the mass on one side of our universe winds up canceling out the gravity from the mass on the other side.

 

So, you wind up with two possible scenarios: An even distribution of mass outside of our universe, in which case the gravity cancels out and it cannot be the cause of expansion.

 

Or an uneven distribution, in which case it can exert a gravitational pull on matter within our observable universe, but biased in a particular direction, in which case it cannot be responsible for the isotopic expansion we observe in our universe.

[Lord Antares]

 

Dark energy is just a placeholder for whatever turns out to be the explanation. This could some form of energy, it could be a change to the way gravity works, it could be something else.

 

This! I wish more people understood this. The resulting finding would not be called dark energy, but something else entirely, depending on what it is.

Same goes for dark matter. It's the same as saying ''we don't know what's causing this''.

[fred2014]

My replies are sparse here as I'm having trouble getting the quoting system to work and end up doing it all manually.

(Not a fault I just can't get my head around it)

 

I still don't think shell theorum applies but I'll spend more time understanding it better.

On the other hand - who is to say what gravity does outside of gravity wells entirely.

As far as I know we can't have any frame of reference for that beyond guesswork.

 

OK - a citation was asked for - this was something I read and asked about some time ago however I've gone away and

looked for something I can actually quote - and it just so happens the "New Scientist of March 2017" is right on our doorsteps.

 

Page 30 regarding the bullet cluster:

"But in recent years dissenting voices have said the ferocity of the collision is impossible

in a universe dominated by dark matter. In fact tweaking the laws of gravity might better

explain this smash-up"

 

P.31

"Vera Rubin saw that Newtons gravity is not enough in the 1970's"

 

I suggest a read of pages 32-33 also.

(If you need me to quote more let me know.)

If I sound a little smug here - my apologies. The magazine seems to be saying

what I've been suggesting for some years.

 

You might also want to look into the concept of MOND (Modified Newtonian dynamics)

It bears looking at again I think.

 

I just think like string theorist - scientists have thrown science out the window

in favour of whatever untestable science fiction will draw down the biggest budgets.

 

PS (Sorry I dont have time to watch online videos)

[Strange]

Both dark matter as matter and as modified gravity ARE being looked at. Until we have definitive answer they will both continue to be developed and tested (i.e. by doing science). In fact, because this is science, people will continue to question and test both ideas even after we have a "definitive" answer.

 

There is nothing untestable about any of the dark matter hypotheses.

[fred2014]

Can't see it, can't register any effects, don't know what it's made of, don't know where it is.

But if we make up enough if's but's and maybe's we can fit it into

the empty hypothesis box we have over here.

 

There is a phenomenum you don't understand - fair enough - but you don't go on a snark hunt

untill you've killed all the wild boar.

 

Some say gravitational lensing indicates the existance of dark matter. Once again the

tail is put before the horse because it seems to fit.

 

The trouble with "doing science" is people are programmed to believe anything with

the term "science" in is de-facto correct.

"Doing Science" is the practice of "having a guess" and when it's wrong "having another guess"

until you guess close enough to to what you wanted in the first place then you're happy.

 

In engineering terms - it's a closed system with positive feedback.

Sometimes - Inevitably - you end up with 11 dimensions and a galaxy full of fairy dust.

 

Searching for "dark matter" is not the same as searching for things in the LHC.

 

As much as it pains me to say it - I think this is one situation where a bit more

creativity with math and concepts might prove usefull.

[StringJunky]

Can't see it, can't register any effects, don't know what it's made of, don't know where it is.

But if we make up enough if's but's and maybe's we can fit it into

the empty hypothesis box we have over here.

 

There is a phenomenum you don't understand - fair enough - but you don't go on a snark hunt

untill you've killed all the wild boar.

 

Some say gravitational lensing indicates the existance of dark matter. Once again the

tail is put before the horse because it seems to fit.

 

The trouble with "doing science" is people are programmed to believe anything with

the term "science" in is de-facto correct.

"Doing Science" is the practice of "having a guess" and when it's wrong "having another guess"

until you guess close enough to to what you wanted in the first place then you're happy.

 

In engineering terms - it's a closed system with positive feedback.

Sometimes - Inevitably - you end up with 11 dimensions and a galaxy full of fairy dust.

 

Searching for "dark matter" is not the same as searching for things in the LHC.

 

As much as it pains me to say it - I think this is one situation where a bit more

creativity with math and concepts might prove usefull.

The problem is quite simple: there isn't enough mass. Dark matter is the placeholder name for that missing mass. People like you are just going to have to wait until they figure out what the 'dark' bit is.

[Strange]

Can't see it, can't register any effects, don't know what it's made of, don't know where it is.

 

 

Of course we can measure effects: that is why "dark matter" (whether that turns out to be matter or a modification to gravity) is hypothesised. And we do know where it is.

 

What should we do? Just ignore the evidence? Or try and find ways of explaining it? And then test those explanations to find which is the best? Because the latter is how science works. Like it or not.

 

 

There is a phenomenum you don't understand - fair enough - but you don't go on a snark hunt

untill you've killed all the wild boar.

 

What does that even mean?

 

 

The trouble with "doing science" is people are programmed to believe anything with

the term "science" in is de-facto correct.

 

Maybe some members of the public think like that. If so, it is a failure of science communication and science journalism.

 

It is hardly relevant to the discussion of the way science is done, though.

 

 

"Doing Science" is the practice of "having a guess" and when it's wrong "having another guess"

until you guess close enough to to what you wanted in the first place then you're happy.

 

Close. Except the guesses are based on evidence and theory. Then they are tested. As you say, if they don't work they are discarded.

 

 

Searching for "dark matter" is not the same as searching for things in the LHC.

 

Why not?

 

People are searching for dark matter as new types of particles (quite exciting), which might also turn up in the LHC.

 

People are also searching for dark matter as changes to our understanding of gravity (more exciting) - that probably doesn't have any connection to the LHC.

 

People are also searching for dark matter as totally new physics (most exciting of all) - which may or may not have any connection to the LHC (as we don't know what that new physics might be).

 

 

As much as it pains me to say it - I think this is one situation where a bit more

creativity with math and concepts might prove usefull.

 

Given the wide range of possible solutions being chased, that doesn't seem like a reasonable criticism. What line of research do you think is being missed?

[Phi for All]

If I sound a little smug here - my apologies. The magazine seems to be saying

what I've been suggesting for some years.

 

It's probably somewhat like the smugness we feel seeing you confirming your own mistaken biases all these years. You seem to have a limited understanding of science, but very few qualms about assuming it's entirely motivated by the biggest budgets and protecting mistaken concepts.

 

I get it. You just saved yourself decades of study into what science really is, and all you had to do was ignore what really goes on, easy-peasy.