# The Naked Scientists Forum

### Author Topic: Could Dark Energy and Gravity be the same thing?  (Read 5435 times)

#### Jon Francis

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##### Could Dark Energy and Gravity be the same thing?
« on: 09/08/2010 03:09:28 »
Imagine two travellers being pushed out into the expanding space after the big bang. They initially are traveling parallel but as space expands they begin to move away from each other sideways. Like a missile fired into the sky their motion is slowed by gravity. As they look towards each other they see they are moving apart and as gravity reclaims them, to each other they seem to be moving apart at increasing velocity while in fact they are being pulled together. Is this what we see? and is the universe contracting while it seems to us that it is expanding at an increasing rate?

#### Soul Surfer

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##### Could Dark Energy and Gravity be the same thing?
« Reply #1 on: 09/08/2010 17:27:53 »
I think I see your point and it is an interesting idea but I think it is flawed.  If this was happening it would mean that we are in a particular position with respect to the expansion from a centre some distance away and although your idea might work in one preferred direction the results in all directions would be asymmetric this does not tally with the observations so another good idea bites the dust.

#### Jon Francis

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##### Could Dark Energy and Gravity be the same thing?
« Reply #2 on: 09/08/2010 19:59:06 »
Maybe but imagine the expansion in the form of a bubble. On the bubbles surface all points expand away from each other. When gravity reclaims them they would be pulled back into the bubble while still stretching space between them. Think of a balloon pinched between two fingers. The compression stretches the bubble where the fingers approach each other while squeezing out the rest of the bubbles surface further. If two points are contracting and they watch each other they would appear to be moving apart when looking across the stretching surface of the space bubble.

#### Soul Surfer

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##### Could Dark Energy and Gravity be the same thing?
« Reply #3 on: 09/08/2010 22:12:47 »
That would imply that space was distorted in  a way different from the known distortion due to gravity and there is no evidence for this

#### Kelvinjohnson

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##### Could Dark Energy and Gravity be the same thing?
« Reply #4 on: 04/10/2010 01:31:35 »
Let me start by saying I enjoyed reading your thought experiment Jon & Soul Surfer your succinct well informed reply & insights.  I have been mulling over a similar thought experiment for some time & would highly value your input..

If I imagine space time (and any number of other dimensions we may like to add in to describe our Universe) as being of a given initial density for a set initial volume. Then if the volume of the Universe contracts, the density of space time will increase. Furthermore that density would increase at an accelerated rate given a constant linear decrease in the Universe's overall spatial lengths (which admittedly I think only an observer outside our Universe could measure). If we were inside this construct then would it not appear to us that non gravitationally bound galaxies would be receding from us at an accelerating rate with respect to 'distance' from us due to the increasing density of space time?

#### CPT ArkAngel

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##### Could Dark Energy and Gravity be the same thing?
« Reply #5 on: 05/10/2010 05:03:08 »
In order to stretch or contract spacetime, you need some force to do it. According to some observations, it seems that every large astronomical objects are moving away from each other (redshift by Doppler effect) at an accelerated rate. It just mean that the spacetime length appear to be longer at an accelerated rate (for any density of spacetime)... If the Universe is contracting in density of SpaceTime, distances between objects would decrease accordingly. If it expands in density (lowering density) the distances would increase accordingly. Our measurement of a meter would still be a meter for us but not from an outsider of the Universe. So it means, you sill need something like gravity or another force to move objects apart. This is a problem of perception because people look at it from outside the Universe, but, in fact, we are inside of it...
« Last Edit: 05/10/2010 20:49:12 by CPT ArkAngel »

#### kenhikage

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##### Could Dark Energy and Gravity be the same thing?
« Reply #6 on: 05/10/2010 05:35:19 »
What I don't understand, about the normal way of thinking of expansion, is if space-time itself is expanding, then shouldn't things appear not to move away from each other?

I mean, if two objects are a meter apart and you stretch the (meaning of a) meter, then those two objects are still just as far apart from each other within that system. It's only from outside the system that a meter has seemingly changed.

So, since things do appear to move away from each other (redshift) doesn't that mean that the objects are actually moving through that dimensional medium; e.i., the distance is increasing.

#### CPT ArkAngel

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##### Could Dark Energy and Gravity be the same thing?
« Reply #7 on: 05/10/2010 05:51:29 »
exactly...

But the usual expanding Universe is not a stretching of spacetime but rather an expansion of it (more and more spacetime is created as objects are moving apart from each other). This is the Forces that are acting on the density of spacetime. My theory :) is that a substantial amount of Dark Matter is at the edge of the Universe. Its gravitational energy is causing the accelerated redshift of the objects we are seeing because they are in the middle of the Universe... see my explanations: http://www.thenakedscientists.com/forum/index.php?topic=34076.0
« Last Edit: 05/10/2010 06:12:57 by CPT ArkAngel »

#### kenhikage

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##### Could Dark Energy and Gravity be the same thing?
« Reply #8 on: 05/10/2010 06:05:46 »
exactly...

But the usual expanding Universe is not a stretching of spacetime but rather an expansion of it (more and more spacetime is created as objects are moving apart from each other).

Way to go and shatter my fragile view of everything.

Actually, now I understand what was wrong with my thinking. So it seems as if space-time is made out of nothing, and thus we label that wellspring dark energy, right?

#### CPT ArkAngel

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##### Could Dark Energy and Gravity be the same thing?
« Reply #9 on: 05/10/2010 20:24:58 »
No, Dark Energy is the unknown energy that is accelerating the expansion of the Universe. Without such energy, the expansion should be decelerating due to gravity of all objects within the Universe. Dark energy can be anything, but it is probably, either, gravitational force from objects at the edge of the Universe (or outside) or a fifth force (a kind of ultra weak anti-gravitational force) acting on some or all types of particles.
« Last Edit: 05/10/2010 20:27:01 by CPT ArkAngel »

#### Kelvinjohnson

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##### Could Dark Energy and Gravity be the same thing?
« Reply #10 on: 06/10/2010 12:23:42 »
I remember reading somewhere that on a huge scale it appears that some galaxies clusters appear to be 'flowing' in a common direction, a Dark Flow being cause by a concentration of Dark Matter? (both terms being unknown) Or maybe evidence of Space time contracting to a singularity?

#### Soul Surfer

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##### Could Dark Energy and Gravity be the same thing?
« Reply #11 on: 06/10/2010 13:28:16 »
There is no evidence to suggest that this flow would lead to an eventual collapse.   It is more likely that the whole universe has some sort of "shape"  related to its origins.  we can only see a part of this shape and the flow may be an indication of this.

#### Kelvinjohnson

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##### Could Dark Energy and Gravity be the same thing?
« Reply #12 on: 08/10/2010 07:25:59 »
I agree Soul Surfer, and that shape could be a funnel! ;)

#### Soul Surfer

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##### Could Dark Energy and Gravity be the same thing?
« Reply #13 on: 08/10/2010 08:32:39 »
my personal opinion is that the most likely shape for the universe is a thinnish toroidal surface of which we can only see a part of its thickness  and the flow could be the shear in the coherent net spiral motion of all material around that surface.  However that is not part of a generally accepted property of the universe.

#### kenhikage

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##### Could Dark Energy and Gravity be the same thing?
« Reply #14 on: 08/10/2010 11:44:41 »
Haven't I read that as two bodies approach each other, time slows down. So the satellites involved in GPS have to be running on a slightly differently tuned clock than we on earth do.

So with that, two bodies moving away from each other experience time as speeding up. Could that account for the acceleration?

#### Kelvinjohnson

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##### Could Dark Energy and Gravity be the same thing?
« Reply #15 on: 09/10/2010 09:24:42 »
Hi Kenhikage. As Time (as measured by a repeating process such as the tick of a clock, oscillation of an atom or even a drip from a bucket that has a small hole in the bottom & the water level in the bucket is kept at a constant height / head) is as Einstein showed, not a fixed global commodity but is Relative (refer Theory of Relativity, both Special & General). As an object speeds up the passing of time slows down relative to (and let's keep this uncomplicated) a stationary observer.  If 2 objects speed away from each other or towards each other & both accelerate & travel at the same speed then the passing of time each experience (relative to each other) is the same. Closer you get to the speed of light the more time (relatively) slows down, a photon of light experiences no passing of time.

A gravity field acts like acceleration. Time passes for your head at a different rate as to your feet when standing up. Lying down at the same rate.  Cool eh?!

#### kenhikage

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##### Could Dark Energy and Gravity be the same thing?
« Reply #16 on: 12/10/2010 07:41:49 »
Right... Maybe you explained the error in my thinking, but I though I took everything I just read into account. Maybe I didn't actually understand. Let me try again just to make sure.

We experience everything as leaving us (redshifting). And everything seems to be going away at with acceleration (caused by dark energy). But, as things move away from an observer, time seems to pass faster (right?). So, couldn't the acceleration be an illusion cased by time dilation? That is, perhaps the Universe is expanding, but not accelerating.

Most likely these kinds of things are already taken into account.

#### Kelvinjohnson

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##### Could Dark Energy and Gravity be the same thing?
« Reply #17 on: 17/10/2010 07:14:55 »
It is believed that space itself is expanding / being created. Kind of like tectonic plates that are moving apart, if I can use that as an analogy. The land mass sitting on those plates are being carried along with the plate with more crust being creating at the point the plates are separating. Similarly space is being created everywhere pushing everything apart (ignoring gravitational bound objects). The amount of additional space being created between 2 points over a given interval of time is proportional to the amount of space there is between those 2 points.  So if there was a 100 units of space between 2 points and new space was being added at 10% for a given time interval then over that interval of time the 2 points would be 10 additional units apart. If they were initially 1000 units apart they would now be 100 units further apart over the same interval of time and if they were 10,000 then 1000 units further apart and so on.  The theorized reason for the acceleration is that as time passes more space is being created which then positively feeds back on itself allowing even more space to be created. The redshift is the stretching/addition of space through which the photons are traveling. Write the word "photon" on an elastic band & stretch it, that's the redshift.

#### Bill S

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##### Could Dark Energy and Gravity be the same thing?
« Reply #18 on: 26/10/2010 19:30:53 »
Quote from: ArkAngel
My theory :) is that a substantial amount of Dark Matter is at the edge of the Universe. Its gravitational energy is causing the accelerated redshift of the objects we are seeing because they are in the middle of the Universe

This is reminiscent of the "Falling Galaxies" theory of Donald Hamilton (http://novan.com/cosmol.htm) in which he says:

"There is a Super Attractive Force, at the boundary of the universe that powers the Universe. It is the primary source of all the energy in the Universe. Although it is similar to gravity it is not gravity......This Super Force causes all galaxies to accelerate (fall) toward the boundary under the complete influence of Inertia (the Inertial Requirement of Space). As the body accelerates it acquires mass and therefore gravitational power.
It is well known that bodies falling for long distances in a gravitational field tend to separate from each other because the bodies closer to the source of attraction are in a slightly stronger gravitational field than the trailing bodies causing them to accelerate faster.
This causes a gradual separation of the bodies over long periods of time and vast distances. If the Super Attractive Force, is located at the boundary of the universe, all the galaxies would be accelerating (falling) outward toward this boundary."

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##### Could Dark Energy and Gravity be the same thing?
« Reply #18 on: 26/10/2010 19:30:53 »