What Does It Mean When We Say Empty "Space" is Expanding?

[notknowing]

This was moved from another thread in the relativity forum, as it isn't about relativity - pervect.

I have a question - with some concerns over how it may be answered. On other websites, and in other print publications, I've seen Ph.D. physicists and cosmologists misunderstand the question: What does it mean when we say that empty "space" is expanding?Robert

Hi,
I understand your question and your frustration.
The problem arises by misinterpreting a mathematical description of reality (General Relativity) by reality itself. The "pure relativists" will only accept geometry as the basis to describe all physics and it is rather hopeless to discuss your question with them.
I can offer you an intuitive understanding of expansion of space, which does not belong to the mainstream physics, and which can quickly be attacked for that. Therefore, I just want to present it here as an example of a possible way to answer your question.
Suppose geometry is not the final "thing" but that something else is at the basis of (or creation of) geometry. This by itself is not new; it is known under "pregeometry". Suppose that this works as follows. Space itself is not continuous but discrete. It consists of a network of nodes which are interconnected (links). The metric would be related to this for instance by the number of nodes one has to cross to connect one node to some other node. This network is not static. Nodes and their interconnections are changing all the time (type of quantum fluctuations). Expansion of space can then simply be imagined by the splitting of some nodes and a corresponding reconfiguration of its external links. In other words, extra nodes - read space - is created.

 

[pervect]

The first question one has to ask is if this theory makes any experimental predictions. The next question one should ask - are they the same as the experimental predictions of GR, or different?

 

[marcus]

Hello Rudi, welcome to Beyond forum!
I will give you some advice. Here we do not discuss our own ideas as such, for the most part. We normally discuss PROFESSIONALLY RESEARCHED ideas. This is a convenient criterion that allows great freedom and also keeps out a lot of garbage.

So if you like an idea, you can ask people if they know whether it is professionally researched. And they will say yes, so and so, go to arxiv.org such and such.
And then you can go and study the research papers and come back with the same idea as before but now it is Lee Smolin's idea, not yours. And he is paid to research it. So it is professional. And everything is cool.

This leads to lots of interesting discussion. So the basic recipe is if you want to put an idea up for discussion you should supply an arxiv.org link. And you may get discussion or people may ignore it---you win some and you lose some. That is how it goes.

Now your idea is a fairly familiar professionally researched idea that was the basis of Lee Smolin's talk at the October 2005 conference at Potsdam (Albert Einstein Institute) called "Loops 05"

He had three or four people working on this idea and deriving CONSEQUENCES from it that you could compare with reality. And he gave a talk summarizing several peoples work and then later during the afternoon sessions some of them also gave shorter talks.

By now there must be 2 or 3 papers on arxiv.org that derive from this idea. I AM NOT SAYING THAT IT IS A GOOD IDEA OR THAT I PERSONALLY LIKE IT! All I am saying is that if you like it you can hunt around and find professional research papers that explore it.

For starters just say
http://arxiv.org/find/grp_physics/1/au:+SMOLIN_L/0/1/0/all/0/1
and read the abstract of each paper since 2005 and download some pdf of any that are about this. I don't want to make it too easy.

the basic idea is that space is Relationship. it is a web of geometrical relationships between events.
and it started out at around bigbang time as a randomly connected graph or a complete graph with all the points "near" all the other points. and then there are "evolution moves" much as you describe in your post, by which new nodes are added and also "moves" where local reconnections happen (four nodes that are interconnected one way change the way they are interconnected)

and if you choose the "moves" correctly and put the correct probabilities on the different moves happening then the huge messy web EVOLVES and sort of smooths out some so that eventually a typical node will only be "near" a few neighbors and it looks more like a lattice. But there are still IMPERFECTIONS. nodes that have "nonlocal" connection to something that could be in another galaxy. But these nodes are very rare. There might be one in the room with you but compared with the total they almost do not exist.

these nonlocal connections can be used in an attempt to explain some indeterminacy in quantum mechanics. Notice I do not say that any of this is successful! It is a very high-risk line of investigation. But several people at Perimeter Institute do work on it. There are places in the world where you can work on extremely risky ideas.

So anyway, have fun, and don't become too much of a nuisance or nobody will like you
Go and find papers that are in accord with your imagination and study them and then come and try to discuss them with us. You might find someone willing, or might not, but it is worth a try.

 

[notknowing]

Hello Rudi, welcome to Beyond forum!
I will give you some advice. Here we do not discuss our own ideas as such, for the most part. We normally discuss PROFESSIONALLY RESEARCHED ideas. This is a convenient criterion that allows great freedom and also keeps out a lot of garbage.

So if you like an idea, you can ask people if they know whether it is professionally researched. And they will say yes, so and so, go to arxiv.org such and such.
And then you can go and study the research papers and come back with the same idea as before but now it is Lee Smolin's idea, not yours. And he is paid to research it. So it is professional. And everything is cool.

This leads to lots of interesting discussion. So the basic recipe is if you want to put an idea up for discussion you should supply an arxiv.org link. And you may get discussion or people may ignore it---you win some and you lose some. That is how it goes.

Now your idea is a fairly familiar professionally researched idea that was the basis of Lee Smolin's talk at the October 2005 conference at Potsdam (Albert Einstein Institute) called "Loops 05"

He had three or four people working on this idea and deriving CONSEQUENCES from it that you could compare with reality. And he gave a talk summarizing several peoples work and then later during the afternoon sessions some of them also gave shorter talks.

By now there must be 2 or 3 papers on arxiv.org that derive from this idea. I AM NOT SAYING THAT IT IS A GOOD IDEA OR THAT I PERSONALLY LIKE IT! All I am saying is that if you like it you can hunt around and find professional research papers that explore it.

For starters just say
http://arxiv.org/find/grp_physics/1/au:+SMOLIN_L/0/1/0/all/0/1
and read the abstract of each paper since 2005 and download some pdf of any that are about this. I don't want to make it too easy.

the basic idea is that space is Relationship. it is a web of geometrical relationships between events.
and it started out at around bigbang time as a randomly connected graph or a complete graph with all the points "near" all the other points. and then there are "evolution moves" much as you describe in your post, by which new nodes are added and also "moves" where local reconnections happen (four nodes that are interconnected one way change the way they are interconnected)

and if you choose the "moves" correctly and put the correct probabilities on the different moves happening then the huge messy web EVOLVES and sort of smooths out some so that eventually a typical node will only be "near" a few neighbors and it looks more like a lattice. But there are still IMPERFECTIONS. nodes that have "nonlocal" connection to something that could be in another galaxy. But these nodes are very rare. There might be one in the room with you but compared with the total they almost do not exist.

these nonlocal connections can be used in an attempt to explain some indeterminacy in quantum mechanics. Notice I do not say that any of this is successful! It is a very high-risk line of investigation. But several people at Perimeter Institute do work on it. There are places in the world where you can work on extremely risky ideas.

So anyway, have fun, and don't become too much of a nuisance or nobody will like you
Go and find papers that are in accord with your imagination and study them and then come and try to discuss them with us. You might find someone willing, or might not, but it is worth a try.

Hi,
Thanks for welcoming me. I was not familiar with the work of Lee Smolin, so thanks for the references which I will study more closely. You mention that the idea comes from Smolin but I'm not so sure of this. I have been putting these exact ideas on my personal website since 11 July 2004, so before his 2005 papers and presentations. Even the imperfections - nodes that have "nonlocal" connection to something that could be in another galaxy - were already mentioned in my website since 11 July 2004. So, so long for the " PROFESSIONALLY RESEARCHED ideas" which may well be based on my unprofessional ideas. In any case, I'm glad to learn that people are working on these ideas.