OT: Gravity, Dark Energy, Universal expansion
 

I was driving home from the city a while back, thinking about (of all things), gravity, dark energy and the expansion of the universe. I know, rather odd things to be thinking about on an hour and a half long drive, but hey, that's me. http://forum.shrapnelgames.com/image...ies/tongue.gif

The theory I came up with is this, of which I have no clue if it's possible, probable, or I'm just totally out to lunch.

Scientists have been searching for the cause of the increasing speed of the expansion of the universe for some time now, dubbing the force responsible for it "dark energy". Dark Energy Wikipedia Link My thought was...what if this expansion isn't caused by some unknown force, but instead is simply another aspect of an already familiar, but far from understood force. Gravity.

Everyone knows that, on the scale of us, our planet, our solar system, even super clusters of galaxies, gravity tends to reign supreme, holding everything in a relatively cohesive unit. However, it weakens as the square of the distance between two objects. So over massive distances, gravity from an object is essentially nil on another distant object. Unless I'm terribly wrong, gravitational force is currently thought to approach zero, but never actually reach zero (to become infinitely close, but never reach).

What if, instead of simply becoming incredibly weak over massive (billions of light-years) distance, gravity essentially reversed itself. It's look something like this...please excuse the horrible little graph, I whipped it up in about 3 minutes with Paint http://forum.shrapnelgames.com/image...ies/tongue.gif

http://img222.imageshack.us/img222/9341/87277130qe6.jpg

So instead of a mysterious force permeating space, causing an expansion of increasing speed, gravity, once the universe expanded sufficiently from the Big Bang, would expand due to, of all things, the gravity that also holds it together.


Now, feel free to blow holes in my wee theory, in fact, I hope you do. I just thought it was an interesting idea, that's more than likely impossible. Though, we really don't have any idea of how gravity actually 'works', so...who knows!

Re: OT: Gravity, Dark Energy, Universal expansion
 

/me votes for 'Unprovable, a little silly, but a fun idea'.

Re: OT: Gravity, Dark Energy, Universal expansion
 

I voted that I like it, but what I mean is I like the idea that someone else thinks about this stuff like I do and as to why it might happen. I don't think the theory is solid, but a cool thought in any case.

Re: OT: Gravity, Dark Energy, Universal expansion
 

Of course it is gravity! What was the Disney movie, outside of the black hole? The weird robot one? I am more thinking of traffic, or should I finally get XM? I have heard a theory that the moon stabilizes Earth, and it is slowly,flowing away. Why do I feel like I am living on a ping ball. Well we are, on a grand scale.....

Re: OT: Gravity, Dark Energy, Universal expansion
 

I too contemplate things when I drive only I concentrate on Philosophy and sociology. I suppose since I can't understand people's motivations I try to come up with reasons for things, but enough of that.

I have always thought Dark matter is a bit suss. Physicists were studying space and couldn't come up with a reason for what appeared to be, and this might be extremely exagerated, 95% of the universe's weight. It just seems to me to be cheap that they then explain

"oh well the thing is there is this thing called Dark matter that makes up all the extra weight, only we can't detect it or see it. It makes our sums add up though if we assume it exists" http://forum.shrapnelgames.com/image...s/rolleyes.gif

Pity I wasn't taught such a thing in college.

"oh well on the face of it my math doesn't add up but you see there is an unseen variable that if included results in 1+1=3"

All I know of Gravity is that it is the weakest of the 4 forces. After all the entire gravity of Earth acts on us yet we can easily lift things, dependent on weight, and lift our own mass.

Re: OT: Gravity, Dark Energy, Universal expansion
 

A magnet less than an inch around can lift its own weight against the force of the entire earth. If memory serves, gravity is about a million times weaker than magnetism. On the other hand, gravity goes a lot farther than magnetism.

Re: OT: Gravity, Dark Energy, Universal expansion
 

I think I may have heard this "gravity goes from pulling to pushing at extreme ranges" theory before, but I don't know if it was disproved or is still around or what. A bit of googlage may find someone who has done some work on it.

Actually, the moon is falling, very very gradually. Every orbit it gets a tiny bit closer to Earth. Eventually, it will drop out of the sky and crash into us.

Of course, that's a long long way in the future. In fact, I think the sun will move into the next phase of its life by then, expanding to scorch and swallow up the inner planets (including us) so you've got a good few billion years to worry about it yet...

Re: OT: Gravity, Dark Energy, Universal expansion
 

That was The Black Hole. http://forum.shrapnelgames.com/images/smilies/cool.gif

Re: OT: Gravity, Dark Energy, Universal expansion
 

No, it isn't. It's drifting away at a rate of 1.5 inches per year. The reason for this is conservation of angular momentum as the Earth's spin slows down due to tidal friction.

Re: OT: Gravity, Dark Energy, Universal expansion
 

Looks like a variation on MOND (http://en.wikipedia.org/wiki/Modifie...onian_dynamics).

Re: OT: Gravity, Dark Energy, Universal expansion
 

The moon would only be drifting closer if it started out inside geosynchronous orbit. Since in that case it would be going around more than once per day, and thus pull the surface along.
It would thus spin up the earth at the expense of its own orbit until doomsday.

Re: OT: Gravity, Dark Energy, Universal expansion
 

Interesting gravity talk. I am in the process of reading A Fire Upon the Deep. Has some interesting gravity concepts in there.

Re: OT: Gravity, Dark Energy, Universal expansion
 

Dark Matter and Dark Energy are bad science... they are no more than the flying spaghetti monster outside religion.

Basic Logic dictates something the *fudge* is wrong...
Gravity was confirmed because everywhere in the universe we looked, things behaved as gravity predicted.
Dark Matter is now confirmed because everywhere in the universe we look, things do not behave as gravity predicted.
That reasoning is Paris Hilton daft... and people are getting PhD's for it.

It is important to note:
distances and velocities in astrophysics are not beyond question... lots of assumptions, and simplifications, with little attention to other factors that could skew the results. I would question these long before adding new material to universal model.

Also, has anyone bothered to measure the net charge of a galaxy? or the interaction with the galactic magnetic field with the extragalactic wind? Gravity isn't alone in the universe...

Dark Energy is worse... especially with that horrid little article that made the news, about a tipping point where all matter would fly apart at the speed of light. Total nonsense, that 'theory' claimed a density of dark energy that resulted in more dark energy as the universe expanded. Poppycock! Space having an inherent density of anything violates relativity, since volume is not a constant in all reference frames.

*grumble*

Re: OT: Gravity, Dark Energy, Universal expansion
 

As far as the universe goes, we havn't even got out into our yard.

Re: OT: Gravity, Dark Energy, Universal expansion
 

We can barely see the yard. We're still stuck in our crib. http://forum.shrapnelgames.com/images/smilies/happy.gif

Re: OT: Gravity, Dark Energy, Universal expansion
 

...So THAT'S why there's so much whining, screaming and hitting going on.

Re: OT: Gravity, Dark Energy, Universal expansion
 

If the universe is expanding at the speed of light perpendicular to three-space, then the size of the universe in any direction is increasing at pi times the speed of light. This means that "you can't get there from here" is literally true for most of the universe.

Re: OT: Gravity, Dark Energy, Universal expansion
 

I think you are on crack because while i understand most of the words you are using, using them in conjuction drives me kinda insane :p

Re: OT: Gravity, Dark Energy, Universal expansion
 

The universe expands like the surface of a 4D balloon, with the surface being three-space.

http://farm3.static.flickr.com/2417/...1705b2cb_o.jpg

But the rub is... not only is the far side of the universe is 'farther away' than the big bang... it is so far away that light from one side will never meet light from the other... an effective 3.1415c receding velocity due to spatial expansion.

Re: OT: Gravity, Dark Energy, Universal expansion
 

I tend to have that effect on people from time to time http://forum.shrapnelgames.com/image...es/biggrin.gif

Re: OT: Gravity, Dark Energy, Universal expansion
 

The big bang didn't occur in some particular part of spacetime, but rather it is when everywhere was the all the same place.

It makes no sense to say that something is twice as far away as the big bang.

Re: OT: Gravity, Dark Energy, Universal expansion
 

Yes it does... since in this context time = space (with a factor of c). The big bang was ~20 Billion years ago which makes it 20B*c far away [time] vs the farthest point in the universe which would be 20B*c*pi [space] (1/2 the circumference 2pi*r of the sphere described by r being the time since the BB [*c]).

Re: OT: Gravity, Dark Energy, Universal expansion
 

Come on, man.

Its not 20B light years away.
Its 20B years away.
Those are completely different units.

The size of the *visible* universe (roughly, time since photons were released * speed of light) is different from the size of the universe (which depends on its topology)!

Also, you are stating that there exists a farthest point in the universe from somewhere. This implies that you are assuming a closed universe. Why? Evidence indicates a flat or very slightly open universe last I checked.


The crux of the matter is that "speed of light perpendicular to 3-space" is nonsensical, since distance and speed are both undefined for that.

Re: OT: Gravity, Dark Energy, Universal expansion
 

In my first post I said, "for the universe expanding at the speed of light"... which is an assumption. The rest follows from the balloon model of an expanding universe (the diagram above). In this case, the balloon model is an expanding 4-sphere [due to symmetry the number doesn't matter... it could be any n-sphere n>3], where the balloon's outer surface is 3-space.

Yes, the size of the visible universe is different from the size of the universe, which as I said, can make the universe untraversable... that is was one of my main points.

However, for an n-dimensional balloon model of the expanding universe, it does not by any means imply a closed universe, only a finite one... it can still be open if it expands forever. In any manifold/topology, any point can still have a farthest point... like two opposite sides of the balloon... it is a matter of spatial symmetry, and has nothing to do with the openness. Every point on a circle, or sphere, or n-sphere has a farthest point.

"speed of light perpendicular to 3-space" is not nonsensical, just non-physical... imagine a balloon who's radius is expanding at the speed of light. Mathematically, that perpendicular-ness allows speed and distance to be defined for more dimensions using the same symmetry that allows time being the 4th dimension (ie time= distance/c).

r^2 = x^2+y^2+z^2 where r=c*t (t being the age of the universe)
as t increases, any two "fixed" points (x1, y1, z1) and (x2, y2, z2) will be moving away from one another.

(Personally, I would like to draw the light cones for that diagram, but the curves are pretty hard to photoshop.)

Re: OT: Gravity, Dark Energy, Universal expansion
 

Presuming all of your topology and a fixed rate of expansion, why are you measuring "distances" through your time axis?

Go far enough back in time... and you start going forward again, but on the opposite side of the universe?

My problem is that you are mixing a space dimension with a time dimension.
You can't travel through the middle, since that is time travel. And you're measuring through to negative time which is definitely not right.

Re: OT: Gravity, Dark Energy, Universal expansion
 

In polar or spherical coordinates, r is often constrained to the positive values. Space and Time can be 'mixable' in General Relativity, since the transformations and behavior of distance and duration are essentially the same... and especially since the radial coordinate axis is "unreal" and choosing a measure of space or time (which have a 1:1 correlation) is unimportant. The past doesn't exist anymore, and the old space doesn't exist either. Whether one of the two is more conceptually real is unimportant to the math.

Yes, you can't travel through the middle, only the surface of the sphere is the universe, there is nothing else, unless you want the philosophical definitions that inside of the balloon is the past and outside the balloon is the future. However, you can also choose the philosophical definitions that inside the balloon are old universes and outside are coming universes.

Re: OT: Gravity, Dark Energy, Universal expansion
 

So, back to my initial issue: "twice as far away as the big bang" is absurd.

Re: OT: Gravity, Dark Energy, Universal expansion
 

There is a 1:1 correlation between space and time, especially in this example. From an observer, the big bang is seen through space, at a distance. However, the objective and unobservable size of the universe is larger than that... and it can be over twice that observed distance.

Still it is semantics... so don't worry about it. If you understand my example, it would be better to ask... can the universe be continuous if it is un-traversably large, or is there some sort of mega-macroscopic quantization going on, which could imply some sort of emergent macro-forces might exist. http://forum.shrapnelgames.com/images/smilies/wink.gif

Re: OT: Gravity, Dark Energy, Universal expansion
 

Aside from your negative time problem, I guess the issue is in trying to relate your model to reality when it is just too different.

Re: OT: Gravity, Dark Energy, Universal expansion
 

There is no negative time problem for an expanding 4 sphere surface just like a pocketwatch doesn't prove time travel is possible.

http://www.astro.ucla.edu/~wright/Balloon2.html
http://en.wikipedia.org/wiki/Metric_..._balloon_model

Re: OT: Gravity, Dark Energy, Universal expansion
 

You're the one who said "twice as far away as the big bang" http://forum.shrapnelgames.com/images/smilies/wink.gif


Anyways...

I think the original point is that indeed there are places you can't get to from here.

Assume space is expanding at 20% per year, just for example, and the fastest you can go is 1 light year per year.
In such a case, attempting to travel to Sirius (8.6 ly away) is a bad idea.

Completely ignoring the compound interest you'll suffer:
In the first year, you'll get 1 lightyear along on your journey, leaving 7.6, but in the meantime that 7.6 will have stretched to 9.1
Light trying to get here from Sirius will suffer the same fate, and we wouldn't be able to see it.

Re: OT: Gravity, Dark Energy, Universal expansion
 

I still wonder if that complete inability for two separate places in the universe to interact could cause some sort of spatial bifurcation (splitting of space)... very loosely analogous to the spontaneous splitting/radiating of a nucleus.

Re: OT: Gravity, Dark Energy, Universal expansion
 

If you had a set of points, A, B and C, where A and B were right at the limit of losing contact, and B and C were right at the limit of losing contact. B is located right in the middle between A and C.
A <-> B <-> C

Even though A and C can no longer see point B, you couldn't split the universe near B, because B would certainly notice http://forum.shrapnelgames.com/images/smilies/happy.gif

PS:
Of course, if there was some sort of a crack in spacetime, B would hardly be in a position to complain to management about it http://forum.shrapnelgames.com/images/smilies/wink.gif

Re: OT: Gravity, Dark Energy, Universal expansion
 

Very true... but I was sort of referring to a radiative cross section... perhaps even a tipping point for spatial continuity. I guess a crack in spacetime might be one result.

Re: OT: Gravity, Dark Energy, Universal expansion
 

While you would have two regions that are independent, the space between them is still contiguous.

It is entirely possible to be unable to reach point C from point A, but at the same time be able to reach point B from point A and to reach point C from point B.

Re: OT: Gravity, Dark Energy, Universal expansion
 

...And here I thought another thread on physics was convinced there was no space-time, only particles and a void.

Re: OT: Gravity, Dark Energy, Universal expansion
 

space-time happens after you drink the kool-aid. http://forum.shrapnelgames.com/images/smilies/happy.gif

Re: OT: Gravity, Dark Energy, Universal expansion
 

Might not the expansion be exponential (excuse me if I use the wrong word). The edge (14 Billion ly away maybe) might expand 20% but when something is only 8.6 ly away the distance moved might be inconsequential.

in fact since matter can not be created, unless there is a connection to another dimension, then the universe may expand but it has the same amount of matter, therefore imagine a distance written on a balloon. the edge expands but the distance expands at the same rate. to an outside observer it has grown but to something limited to the balloon it is the same distance.

Re: OT: Gravity, Dark Energy, Universal expansion
 

Except that the folks living on the balloon aren't expanding since they are held together by gravity, electromagnetism, and nuclear forces.

Light will take longer and longer to get from each of your distance marks to the next, making it obvious that they are stretching.

Re: OT: Gravity, Dark Energy, Universal expansion
 

I was sort of thinking of that epsiode of Futurama where the universe is in a box. Fry sits on the box and the universe is squashed, but since they are in the universe they don't notice. Only us outside observers. Probably a mistake to consider Futurama scientific fact http://forum.shrapnelgames.com/images/smilies/happy.gif. After all they increased the speed of light.

"That's impossible"
"nothing's impossible. Not if you can imagine it. That's what being a scientist is all about"
"No, that's what being a magical elf is all about"

Re: OT: Gravity, Dark Energy, Universal expansion
 

Given enough energy, matter & antimatter can be created by pair production.

Re: OT: Gravity, Dark Energy, Universal expansion
 

I see. of course I should have said energy cannot be created or destroyed. my mistake.

Re: OT: Gravity, Dark Energy, Universal expansion
 

Just Finished scanning this topic. Gravity is nothing, black holes are mathematical expressions of Newtonian physics. The reality is we have an electric universe that easily explains what we are seeing. The next time you see that Scientist are "surprised" at what they find in outer space please question in your mind if our current theory is correct why are they surprised? The electric universe easily explains what we are seeing and how things work.Try to think past Newton and realize that Gravity is really weak.

http://www.thesurfaceofthesun.com/

http://www.mikamar.biz/book-info/tes-a.htm

Re: OT: Gravity, Dark Energy, Universal expansion
 

Re: OT: Gravity, Dark Energy, Universal expansion
 

I haven't read these, but generally the problem with an EM structure is propagation speed of EM forces being c, creating a lag that doesn't correspond to observation.

Re: OT: Gravity, Dark Energy, Universal expansion
 

I thought they'd just about concluded that even gravity was limited to c?

Re: OT: Gravity, Dark Energy, Universal expansion
 

Unless a lot of old observations were way off... objects appear attracted to about where the mass is, not where it was d/c ago.

Re: OT: Gravity, Dark Energy, Universal expansion
 

Well, the first source starts spouting nonsense by the second sentence. The surface of the Sun is made of neon?

The second beats on astronomers using a classic "straw man" argument, but doesn't go much further than that.

---
Regarding the speed of gravity, general relativity predicts that it's limited to the speed of light. I don't know if it has been successfully measured. I think some observations may have been made of binary pulsars, but again I don't know the result.

Re: OT: Gravity, Dark Energy, Universal expansion
 

There are a number of observations that do indicate that:
http://en.wikipedia.org/wiki/Speed_o...measurement.3F


As MCT mentioned, however, the earth accelerates towards where the sun *is*, not where it was 8 minutes ago.
Otherwise the earth's orbit would be quite unstable, and we'd all go spinning off into space.

So, there seems to be a relativistic effect that mostly cancels out the lag for slowly moving things.

Re: OT: Gravity, Dark Energy, Universal expansion
 

Hmm, I don't get it. Why would the earth's orbit be unstable? I mean, the sun travels at a constant speed, doesn't it? And the gravitational pull is continous, even if there is 'lag'. So the worst thing I can picture is that the earth will be travelling a tiny bit closer to the sun on one side and a little further behind on the other.