OT: Gravity, Dark Energy, Universal expansion

[Renegade 13]

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/images/smilies/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 (http://en.wikipedia.org/wiki/Dark_Energy) 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/images/smilies/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!

[narf poit chez BOOM]

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

[Solymr]

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.

[Mudshark]

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.....

[Randallw]

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/images/smilies/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.

[narf poit chez BOOM]

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.

[dogscoff]

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.


Mudshark said:
I have heard a theory that the moon stabilizes Earth, and it is slowly,flowing away.



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...

[capnq]

Mudshark said: What was the Disney movie, outside of the black hole? The weird robot one?

That was The Black Hole (http://imdb.com/title/tt0078869/). http://forum.shrapnelgames.com/images/smilies/cool.gif

[capnq]

dogscoff said:
Mudshark said:
I have heard a theory that the moon stabilizes Earth, and it is slowly,flowing away.



Actually, the moon is falling, very very gradually.

No, it isn't. It's drifting away (http://www.newton.dep.anl.gov/askasci/ast99/ast99587.htm) at a rate of 1.5 inches per year. The reason for this is conservation of angular momentum (http://www.astronomynotes.com/angmom/s2.htm) as the Earth's spin slows down due to tidal friction (http://bowie.gsfc.nasa.gov/ggfc/tides/intro.html).

[Spoo]

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

[Suicide Junkie]

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.

[aegisx]

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

[MasterChiToes]

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*

[narf poit chez BOOM]

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

[geoschmo]

narf poit chez BOOM said:
As far as the universe goes, we havn't even got out into our yard.

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

[narf poit chez BOOM]

geoschmo said:

narf poit chez BOOM said:
As far as the universe goes, we havn't even got out into our yard.

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


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

[MasterChiToes]

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.

[Ragnarok-X]

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

[MasterChiToes]

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

http://farm3.static.flickr.com/2417/2169871222_a01705b2cb_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.

[Renegade 13]

Ragnarok-X said:
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

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

[Suicide Junkie]

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.

[MasterChiToes]

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



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]).

[Suicide Junkie]

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.

[MasterChiToes]

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.)

[Suicide Junkie]

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.

[MasterChiToes]

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.

[Suicide Junkie]

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

[MasterChiToes]

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

[Suicide Junkie]

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.

[MasterChiToes]

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_expansion_of_space#Ant_on_a_balloon_model

[Suicide Junkie]

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.

[MasterChiToes]

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.

[Suicide Junkie]

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

[MasterChiToes]

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.

[Suicide Junkie]

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.

[narf poit chez BOOM]

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

[MasterChiToes]

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

[Randallw]

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.

[Suicide Junkie]

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.

[Randallw]

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"

[capnq]

Randallw said: in fact since matter can not be created

Given enough energy, matter & antimatter can be created by pair production (http://en.wikipedia.org/wiki/Pair_production).

[Randallw]

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

[Gozra]

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

[narf poit chez BOOM]

Randallw said:
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"


Yeah, so? (http://freefall.purrsia.com/ff300/fv00255.htm)

[MasterChiToes]

Gozra said:
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



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.

[Raapys]

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

[MasterChiToes]

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.

[Spoo]

Gozra said:
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



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.

[Suicide Junkie]

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

There are a number of observations that do indicate that:
http://en.wikipedia.org/wiki/Speed_of_gravity#Experimental_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.

[Raapys]

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.

[Suicide Junkie]

Equal and opposite reactions.

If the sun was perfectly still there wouldn't be a problem. But earth (mostly jupiter, due to mass&distance) pull on the sun too.

If the sun's gravity appears to be coming from where it was 8 minutes ago, that would be slightly in front of us, rather than directly opposite the center of mass.
Accelerating forwards would spin us out into deep space.

[Baron Munchausen]

No, the earth must be moving at the same rate as the sun in order to even be in orbit. So there is no danger of 'slippage' of that orbit due to the sun's movement over time. Remember that (as far as we know) the earth formed from the same cloud of gas and dust as the sun. It has had the same basic motion/momentum from the beginning. And we orbit the center of mass of the whole solar system, not the sun itself. (Yes, that center is probably about 6 centimeters from the center of the sun... http://forum.shrapnelgames.com/images/smilies/happy.gif )While it's true that they have not yet figured out how to prove that gravity propagates at the speed of light, your supposed 'insight' is a misunderstanding of orbital mechanics, not any sort of proof that it propagates faster than light.

[Suicide Junkie]

Its not the angular speed, but a phase shift that I was talking about.

Measurements of Earth's acceleration show that we are accelerating towards the Sun's current position (to the precision of the instruments), not its position 8 minutes ago.
If the acceleration isn't directly in line with the center of mass, then there will be an an angular acceleration component, which is bad news.

PS:
The center of mass is not 6 cm from the center of the sun, but about 500km according to some quick math.
1 AU makes for a very long lever http://forum.shrapnelgames.com/images/smilies/wink.gif

[Baron Munchausen]

The current position of the sun according to what measurement? If it's the visible position of the sun, it's towards where the sun was 8 minutes ago. http://forum.shrapnelgames.com/images/smilies/tongue.gif Have they somehow measured that the earth is moving relative to where the sun is -- 8 minutes travel from its visible position? That would be big news if so, because it would be proof that gravity propagates faster than light. I'm pretty sure I would have heard about this.

And I didn't do any math about where the system's center of gravity is, I was just tossing out a number. The planets do have about 98 percent of the system's angular momentum, but the sun has 99.5 percent of the system's mass.

[Suicide Junkie]

I thought that was obvious given the context.

Basically the Earth's acceleration is not in the same direction as the incident light from the sun.

[narf poit chez BOOM]

It wouldn't be that hard to predict the suns' position in eight minutes.

So. If gravity is found to travel at c and the earth orbits the suns' actual position...Could gravity be 'connected' to the object it came from?

[Raapys]

I'm confused. So there's both experiments that show that gravity is indeed travelling at the speed of light( or close to it ), and actual observations of the opposite?

Then that would indicate, as narf says, that there's some sort of connection to the object it came from. Perhaps gravity 'predicts' where the sun is going to be at the moment it reaches earth?

So if something was to suddenly push the sun out of its original and predictable path, it might take a while before gravity would catch up and start pulling us in the right direction again.

[narf poit chez BOOM]

That's what people are saying. I have little knowledge of the situation - Just trying to make sense of it.

[capnq]

Raapys said: Why would the earth's orbit be unstable?

Because chaos theory gets involved, which I barely understand myself above the buzzword level. This astronomy abstract (http://www.blackwell-synergy.com/doi/abs/10.1111/j.1365-2966.2005.09443.x?cookieSet=1&journalCode=mnr) mentions chaotic orbits, but I'm already lost by the end of the first sentence. http://forum.shrapnelgames.com/images/smilies/confused.gif

[douglas]

One of the most basic assumptions of relativity is that all inertial reference frames are equally valid. Simply choose your inertial reference frame to be one where the sun is motionless, and you can trivially show that the speed of gravity makes virtually no difference to the influence of the sun on any of its planets. Working out how this is compensated for in other reference frames is a bit more work, but the conclusion is guaranteed unless relativity is wrong.

For the speed of gravity to have a significant effect on gravitational interactions, both masses must be large enough to have significant effects on each other so that both have significant acceleration and no inertial reference frame exists where either body is reasonably close to at rest.

[Suicide Junkie]

That's a better description than I could find anywhere else http://forum.shrapnelgames.com/images/smilies/happy.gif

[narf poit chez BOOM]

...What about the inertial reference frame of one object being pulled by the other, which is pulled by the other one...

Sure, it's recursive. But some recursives do have solutions.

[MasterChiToes]

By definition, inertial reference frames can not be accelerated. So, an object being accelerated does not have its own inertial reference frame.

[douglas]

That falls under the "no such inertial reference frame exists" clause, and the speed of gravity does matter for such systems. Technically the Sun is accelerating so no inertial reference frame has it perfectly at rest either, but the difference is small enough on the scale of the solar system that it hardly matters.

[Atrocities]

Even more to consider Link (http://www.foxnews.com/story/0,2933,322254,00.html)

[narf poit chez BOOM]

Acceleration is simply another factor. Just factor it out.

[Suicide Junkie]

The universe doesn't work that way... try throwing a ball on a merry-go-round sometime http://forum.shrapnelgames.com/images/smilies/happy.gif

[MasterChiToes]

You could throw a fancy dress ball on a merry-go-round and it would be super-fun-cool. http://forum.shrapnelgames.com/images/smilies/wink.gif

[narf poit chez BOOM]

A ball on a merry-go-round would most likely be considerably more complex than two stellar objects moving towards each other - Ignoring all other stellar objects)