Physics/cosmology crank visits house

[Solitaire]

Those "objects that are very far away from each other" are still gravitationally attracted to each other aren't they even if only very weakly? So why aren't galaxies being stretched out by spacetime, even if only very weakly?

Moving matter has a wavelength. As the wavelength stretches, matter's
velocity decreases, therefore matter around a galaxy will slow down and
fall to it's core. Also, in moderate graviational fields around galaxies the
expansion of space time slows down quite a bit, may even reverse.

 

[Jethro]

I assumed that WERE growing, too.

For instance, if we'd setup a lightspeed test with mirrors that bounced a beam of light around the entire earth a billion years ago, would we have measured a different speed? IOW, would the earth itself have grown in the past billion years from the expansion of space? I think it would have. I can't imagine anything "gluing" a solid together to any particular size.

When you look at the universe as a whole, you can assume that it is essentially filled with a homogenous gas that has no pressure. If you do this then the result of your analysis is such that the universe is essentially expanding. This is also what we observe.

When you look at formations on the order of the solar system, you can no longer make the homogenous gas assumption. Instead you have to assume that there are large concentrations of matter along with some empty spaces. These large concentrations of matter cause particles (like planets) to move as if they were feeling some force which is described by Newton's law of universal gravitation. As such there is no expected expansion on the scale of even such large structures as our local group of galaxies.

And here's a much better explanation from the Physics FAQ.

 

[BillyJoe]

.....at small distances gravity.....will overwhelm the expansion.....

At small distances does gravity "overwhelm" expansion or does it cancel it out?
Is that what being "gravitationally bound" means - to have the expansion cancelled out by gravity.

..... and at large distances the expansion will overwhelm gravitational attraction.

Ditto.

 

[heath]

And why doesn't the expansion of spacetime stretch out the objects within it (like the dots on an expanding balloon)? Why empty space and wavelengths but not solid objects?

We can see this doesn't actually happen or there would be no apparent expansion. If EVERYTHING expanded then we would only perceive solid state as far as I can see.

Best way to expand the stretching baloon analogy I think is to imagine solid matter as, say, a small ball rolling on the surface of the expanding ballon. It's "speed" will appear to slow down as the sufrace it's in contact with stretches beneath it. Waves, such as EM waves would be "stretched" as they are undulations in the surface rather than object traveling on it... Works for me anyway.

I haven't checked but I'm sure relativity would fix the apperent disparity introduced by the constant speed of light on waves traveling in a stretching medium. (just don't have the maths any more)

 

[garys_2k]

When you look at the universe as a whole, you can assume that it is essentially filled with a homogenous gas that has no pressure. If you do this then the result of your analysis is such that the universe is essentially expanding. This is also what we observe.

When you look at formations on the order of the solar system, you can no longer make the homogenous gas assumption. Instead you have to assume that there are large concentrations of matter along with some empty spaces. These large concentrations of matter cause particles (like planets) to move as if they were feeling some force which is described by Newton's law of universal gravitation. As such there is no expected expansion on the scale of even such large structures as our local group of galaxies.

And here's a much better explanation from the Physics FAQ.

THANKS! That link provided some excellent information, although their discussion of the Hubble Constant probably needs revising now.

Is this forum great, or what!!!

Thanks again.

 

[Soapy Sam]

Paul- Pardon me for lowering the intellectual level of this thread, but could you please explain the "water hardening system" you mention. You are ADDING ca/Mg ions to the water? Why? Or does the expression refer to something completely different?

 

[Paul C. Anagnostopoulos]

Our water is soft and acidic, so it was leaching copper out of the pipes. We added a tank full of crushed granite that the water flows through. No more green water!

By the way, my crank sent me a letter today. It begins:

Dear Fellow intellectual beings:

and includes a paper titled A Helical Frequency. Anyone want to review it?

Lordy, lord.

~~ Paul

 

[Soapy Sam]

The pH increases after flowing through this granite? Why would that be? I would have though a smidgin of washing soda would be more effective. We also have soft water in much of Scotland, often acidic. I never heard of anyone deliberately hardening it. Is this a common practise where you are?