# B Does Mass determine our depth in the fabric of space?

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1. Jul 26, 2017

### genphis

I have not posted for a while,but something has been bugging me. I would like help understanding that if mass makes a dent in the fabric of space, does it mean celestial bodies are sitting at different depths in the fabric, and does that mean the less mass in an object you are then more likely to find it at a higher depth.

More importantly does that imply a top and a bottom? ( as in boundary)

please excuse me if this is nonsense

2. Jul 26, 2017

### phinds

It is nonsense. There IS no "fabric" of space. That's just a VERY poor heuristic used in pop-sci presentation. The extent of nearby mass determines how deep in a gravity well we are but that's all.

3. Jul 26, 2017

### genphis

Thanks for your reply, but deep implies depth and the nearby mass must also sit in a gravity well and if everything was at the same depth it would suggest space is uniformly flat?

4. Jul 26, 2017

### phinds

The only way for everything to "sit at the same depth" in a gravity well would be if there were zero mass throughout the entire universe.

5. Jul 26, 2017

### genphis

understood, so is there a super gravity well created by the most dense body and all other wells are within this ?

6. Jul 26, 2017

### phinds

I have NO idea where you got such an idea. EVERYTHING is within the gravity well of everything else.

Take any body anywhere in space. Techincally, everything within its observable universe has a gravitational influence on it. For all practical purposes only the closest objects have any effect on it and close massive objects tend to swamp the rest of the influences.

7. Jul 26, 2017

### genphis

so the warping of space is pretty much localised and our trajectory through space time is entirely influenced by the sun, whose trajectory is influenced by?

8. Jul 26, 2017

### phinds

Do you think the International Space Station is influenced more by the Sun or by the Earth?

9. Jul 26, 2017

### genphis

i get the point, i was just thinking about the big picture, so black holes are most likely major architects in the shape of the universe, as they are more likely to occur via star processes in more varied locations. thanks for enlightening me.

10. Jul 26, 2017

### phinds

The supermassive BH at the center of galaxies generally make up 1% to 2% of the mass of the galaxy, so for all but the innermost star systems, the black hole has a very small effect. That's after the galaxy has formed. What we don't know is what role the SMBH's play in the formation of galaxies in the first place. That's a major open question in cosmology, as is how the dickens do SMBH's form at all? The formation of the largest ones seem to be a complete mystery

11. Jul 26, 2017

### genphis

Do the largest smbh's not form of normal star processes as per collapsing star?, and do they only consume and not spew out materiel as per Hawkin's radiation?

12. Jul 26, 2017

### phinds

The problem is that stars cannot form that are even remotely big enough to leave a really big SMBH if/when they go supernova and the problem with their growing by "eating" surrounding matter is that things don't fall in directly, they form an accretion disk, not all of which falls in. There hasn't been enough time in the universe so far for such disks to allow the growth of the biggest SMBH's.

We could keep going on this thread until it has turned into a full course on basic cosmology. I would recommend instead that you read such a book or books.

13. Jul 26, 2017

### genphis

maybe it raises a question about the age of the universe, and whether they are remnants of possible older universes ? but thanks again for the information regards genphis

14. Jul 26, 2017

### phinds

No, it does not. Again, read some basic cosmology before forming any theories or floundering about any more. It's best to come at this stuff systematically.

15. Jul 26, 2017

### genphis

I will do some revising on the subjects thanks

16. Jul 26, 2017

### Staff: Mentor

As phinds said, this is a pop science description that is not really useful when you try to work out the actual physics. What's more, even as a pop science description, it only applies to isolated static gravitating bodies. The universe does not fit that description, so even as a pop science description your suggestion does not apply to the universe as a whole.

17. Jul 26, 2017

### genphis

understood, are all the celestial bodies set in decaying orbits around there gravitational influences, i am trying to understand whether the universes motion has direction ( i suspect direction is relative) but i am having trouble grasping the fact that we are falling around the sun and the sun itself is falling around it's gravitational influence and so on, is that correct?

18. Jul 26, 2017

### phinds

It does not. That would imply a prefered reference frame and there is no such thing

It is correct for things that are in orbit

19. Jul 26, 2017

### Staff: Mentor

If you look at an isolated bound system, this is more or less correct. But the universe as a whole is not an isolated bound system.

A given body, like the sun, is part of multiple isolated bound systems. The sun is part of the solar system, which is part of the Milky Way galaxy, which is part of the Local Group of galaxies, which is part of (IIRC) the Virgo supercluster that includes multiple groups of galaxies all bound to each other. At each level, you can view one system as having some kind of orbit in the next larger system.

But, as above, the universe as a whole is not an isolated bound system, so there is no useful sense in which the highest level of bound systems (superclusters) can be said to have an "orbit" in the universe as a whole.

20. Jul 26, 2017

### genphis

so the only uniform direction relates to the expansion of the universe ? thank you for clearing up some of the fog in my thoughts

21. Jul 26, 2017

### Staff: Mentor

There is no direction to the expansion of the universe, as phinds said.

22. Jul 26, 2017

### Mister T

In this case, though, the depth in a gravity well refers to a lower energy, not a lower height.

23. Jul 26, 2017

### genphis

i am curious as to how something can be said to be expanding without relative direction to support the observation?

24. Jul 26, 2017

### Staff: Mentor

The expansion is the same in all directions.

25. Jul 26, 2017

### Mister T

Distribution of dark matter may be the thing that's responsible for the distribution of matter in the universe.