[thedoc (OP)]

Alexander Markov  asked the Naked Scientists:
   
I wish to share my pet idea about the Universe and hear some competent opinions, possibly telling where I have gone wrong. Basically, in my struggle to comprehend the incredibly complicated theories about the Universe and reality, without having mathematical skills, I inevitably end up visualising the picture. It can be pretty confusing as there are legitimate theories that are giving totally different explanations. Therefore, I took the liberty to try it myself.

I am starting from the observed fact that the Universe is expanding due to the expansion of space itself. It is said that space distance between galaxies and other matter is increasing, but when the matter is gravitationally bound together the space between particles and objects is not getting bigger and not causing them to inflate or fall apart (or at least not in the same rate as the empty space).

My idea is: What if there is a link between the expansion of space and gravity?

Imagine that you are crossing a river. Your body is opposing the flow of the water by a force and that is causing ripples in the river. Now imagine that the flow is in every direction and the ripples are everywhere around you. The same way matter may be opposing the expansion of space, causing the fabric of space-time to distort and create gravitational effect. Probably some properties of matter are prohibiting the expansion of space where matter is present, thus acting as breaks causing the distortion. Maybe all that are causing gravity are like little knots of expansion breaking distortion of space-time. When they clump together in bigger objects the combined distortion is resulting in bigger gravitational effects. Bigger masses like galaxies, dust clouds and clusters are regions dominated by gravity so expansion is not felt locally, because it has been restrained.

We can make some speculations using this scenario. For example, probably the inflation period right after the Big Bang was rapidly expanding space before early matter reached the phase that is causing distortion of space-time (gravity), and put breaks on the expansion to the observed rates. We can also assume that with the expansion of the Universe the matter is getting diluted so gravitational breaks per amount of space are getting weaker, which can explain the acceleration in the rate of the Universe's expansion. That means that in the beginning the expansion of the Universe (starting right after the inflation) was much slower, due to much denser matter distribution. If we have shrinking space, the effect would be opposite , so we will have repulsive gravity.

I would not go for more speculations, because I am way out of my depth. I am curious to see what the more knowledgable people can say about it.

Thanks


Alexander Markov

What do you think?

[Pmb]

In the first place the question Is there a link between the expansion of space and gravity is far too vague to respond to. One can connect many different things using a link between the things between them. E.g. there is a link between monkey’s and stars. Want to take a guess how? E.g. atoms which life requires are born in stars and that matter is required for solar systems to form and for life to be created, including monkeys. You can form links between many different things in many different ways so you’ll have to be more clear on that part.

   
I am starting from the observed fact that the Universe is expanding due to the expansion of space itself. It is said that space distance between galaxies and other matter is increasing, but when the matter is gravitationally bound together the space between particles and objects is not getting bigger and not causing them to inflate or fall apart (or at least not in the same rate as the empty space).

Where did you get this idea from? What makes you believe that it’s true? In what sense to you believe that it’s true? E.g. what happens to the orbit of an electron about the nucleus of an atom during one days worth of universal expansion?

[alexbalex]

Pmb,
I generally don't believe in things, I follow the evidence. The idea is only a speculation about something that might be the case (or not). I am not qualified to defend it and was rather hoping other people to talk about it.

About the title- "link" doesn't mean a distant connection in a philosophical context. It implies what is said in the post and more specifically that we can imagine gravity as a direct side effect of the expansion of space.

[Pmb]

About the title- "link" doesn't mean a distant connection in a philosophical context. It implies what is said in the post and more specifically that we can imagine gravity as a direct side effect of the expansion of space.

I've changed my mind. The question isn't vauge at all now that I've thought about it much more. Einstein's equations are used in cosmology to describe expanding space since the Big Bang epoch and that expanding space can be described using the metric tensor. The components of the metric tensor can be thought of as gravitational potentials and the metric thought of as the gravitational field tensor. So I'd say yes. Expanding space is linked to gravity.

I had to take some time to think more about what the term "gravity" means. It's not a term that has a unique meaning.

[Also65]

I guess you are thinking about gravity like a pressure force. I agree. I have the opinion that gravity is a force of pressure that a longitudinal wave produce against a matter which resist to be pass through. Thermodinamical interaction between this pressure wave and that matter creates cyclically variable gravitational fields (concave spaces that expands and contracts cyclically). Best Regards

[Pmb]

I guess you are thinking ...

When responding in a thread with multiple posters its useful to quote the person whose comments you're responding to. Otherwise we have no idea who you're directing your comment to. In this case I can't tell if bny "you" that you're talking to me or someone else.

I've never been sure if there's a diplomatic way to say this or not but your response is meaningless. It's what some of us refer to as word salad. Sorry. 

[Also65]

I guess you are thinking ...

When responding in a thread with multiple posters its useful to quote the person whose comments you're responding to. Otherwise we have no idea who you're directing your comment to. In this case I can't tell if bny "you" that you're talking to me or someone else.

Sorry, you are right, I was responding to Alexander Markov question.

Regards.

[njskywalker]

Space is expanding like a man blowing up a balloon. Now your question is there a link between space and gravity. Think of the man blowing up the balloon expanding space with galaxies inside spreading apart . In order for the balloon to expand there must be air flowing into the balloon from the lungs of the man blowing it up creating a feedback. For every action there is a reaction. So the lungs compressing is what feeds the expansion of the balloon. Now apply this to our universe. Gravity Inward Yin , electro magnetic outward Yang . Feedback

[Pmb]

In order for the balloon to expand there must be air flowing into the balloon from the lungs of the man blowing it up creating a feedback.

That's a very poor analogy.

For every action there is a reaction.

If you're referring to Newton's third law which reads F₁₂ = -F₂₁ then that law was true for all known phenomena at the time. However since then we've had adcances in science and now we know that F₁₂ = -F₂₁ does not always hold true.

So the lungs compressing is what feeds the expansion of the balloon. Now apply this to our universe. Gravity Inward Yin , electro magnetic outward Yang . Feedback

Nope. It doesn't work that way. As I explained above that is a very poor analogy.

[njskywalker]

ok thanks for clearing that up

[Pmb]

Would you like a worked out example of when Newton's third law doesn't work? It takes a bit of work bit I'll do it if you're interested. Newton's third law always holds for contact forces though.

[alexbalex]

Can I bring the clichéd analogy of the rubber sheet and the ball. Ultimately we have a distortion of the rubber plane caused by the mass of the ball. If we imagine the ball as stationery and the rubber sheet moving (meaning the expansion of space) we will get the same effect. Obviously, that happens in all directions. That's how gravity might be a result of the expansion of space.

[Pmb]

Can I bring the clichéd analogy of the rubber sheet and the ball. Ultimately we have a distortion of the rubber plane caused by the mass of the ball. If we imagine the ball as stationery and the rubber sheet moving (meaning the expansion of space) we will get the same effect. Obviously, that happens in all directions. That's how gravity might be a result of the expansion of space.

That's wrong. The space would not expand unless  the mass was causing it. It is mass that causes the expansion of space.

[Pmb]

I am starting from the observed fact that the Universe is expanding due to the expansion of space itself. It is said that space distance between galaxies and other matter is increasing, but when the matter is gravitationally bound together the space between particles and objects is not getting bigger and not causing them to inflate or fall apart (or at least not in the same rate as the empty space).

I think I may have misinterpreted this earlier. What you said here is correct. In fact it’s mentioned in the following article

Misconceptions About the Big Bang by Charles H. Lineweaver and Tamara M. Davis, Scientific American, Mar. (2005)

Neighboring galaxies initially get pulled apart, but eventually their mutual gravity overpowers expansion. A cluster forms. It settles down into an equilibrium size.

They go on to say

What caused the expansion? Many cosmologists attribute it to a process known as inflation, a type of accelerating expansion. But that can only be a partial answer, because it seems that to start inflating, the universe had to be expanding.

[alexbalex]

Can I bring the clichéd analogy of the rubber sheet and the ball. Ultimately we have a distortion of the rubber plane caused by the mass of the ball. If we imagine the ball as stationery and the rubber sheet moving (meaning the expansion of space) we will get the same effect. Obviously, that happens in all directions. That's how gravity might be a result of the expansion of space.

That's wrong. The space would not expand unless  the mass was causing it. It is mass that causes the expansion of space.

I mentioned the expansion of space in brackets as supporting the analogy of the rubber sheet and the ball, imagining that the ball is stationery and space is moving. I am aware that in the classic example the actuall mass is distorting the space, but never heard that mass is causing the expandion of space. Expansion is said to be caused by the dark energy.

Pmb, thanks for the discussion.

[Pmb]

I am aware that in the classic example the actuall mass is distorting the space,
but never heard that mass is causing the expandion of space. Expansion is said to be caused by the dark energy.

When there is spatial curvature, as there is around gravitating bodies that's what's causing the space to become expanded. In a spherical coordinate system the distance between two different values of r is increased when a gravitating body is placed at the origin.

Pmb, thanks for the discussion.

You're most welcome my good  man!

[/quote]

[alexbalex]

Pmb,
When I say expanding space I mean the dark energy fuelled process of increasing the distance between galaxies or any other points on the universe. I never meant to use expansion to describe the changes of the spatial curvature around massive objects. I would call this distortion or stretching. This is where we get confused when I propose a thought experiment in which gravity(aka spatial curvature distortion) is a consequence of the space expansion( dough and raisins analogy). I would like to imagine it as if the presense of an object is hindering the expansion ( which would be happening with or without the object anyway) and space gets dragged and stretched arround the object, and this way appearing as gravity. I know it is counterintuitive and probably wrong, but worth having fun playing with by my opinion. 

[Pmb]

Pmb,
When I say expanding space I mean the dark energy fuelled process of increasing the distance between galaxies or any other points on the universe.

That process happens without the presence of dark energy. In fact before we knew about dark energy we knew and could explain the expansion of space. That’s caused my matter being thrown away from each other.

I never meant to use expansion to describe the changes of the spatial curvature around massive objects.

Then there’s something I don’t understand. Why did you use the rubber sheet analogy for a moving body?

[njskywalker]

sorry matter does not define space. Space defines matter. all energy radiates into space .

[Pmb]

sorry matter does not define space. Space defines matter. all energy radiates into space .

It’s clear from all the posts you made since you’ve started posting here that you have no idea what you’re talking about. So please stop talking about things you don’t understand. That matter defines space is known as Mach’s Principle and is one of the principles on which Einstein built general relativity. As phrased by D’Inverno in his GR tex The matter distribution determines geometry. If there is no matter then there is no geometry