Universe Expansion

[Psnarf]

We've all seen the analogy with bits of paper or dots stuck to a balloon that get farther apart as the balloon expands. However, that's not the way the universe expands. The fabric of spacetime isn't stretched; new spacetime shows up to push the existing spacetime apart, if my feeble understanding of such matters is anywhere close to current cosmology. My question is, where does the new spacetime come from? Everything we know about the universe confirms the tenet that everything is produced by causes and conditions, nothing is created or destroyed, mass and energy are interrelated, and all. I know that particles and antiparticles appear and self-annihilate on the order of 10 to the minus 34 seconds (Planck constant). Does virtual spacetime already exist and gets knocked into observable spacetime by those causes and conditions that produce the Casimir Effect? If the rate of the appearance of new spacetime is everywhere constant, the measured velocity of galaxies would increase with distance, which is what we observe.
(signed) Baffled

[Chris Peterson]

We've all seen the analogy with bits of paper or dots stuck to a balloon that get farther apart as the balloon expands. However, that's not the way the universe expands. The fabric of spacetime isn't stretched; new spacetime shows up to push the existing spacetime apart, if my feeble understanding of such matters is anywhere close to current cosmology

Spacetime isn't a fabric, and it isn't a "thing" that needs to get created. The Universe can expand without requiring "new" spacetime and without anything "stretching". These kinds of analogies come about because natural language is not very effective at rigorously describing cosmological theory. (However, "stretching" isn't a bad term to describe what the math represents; in many respects the expansion of spacetime is very much like stretching- for instance, in the way that photons are redshifted as they travel.)

The balloon analogy is a very good one, but it is intended to help understand the geometry of expansion, not the material properties of the Universe.

[Psnarf]

Thank you for your explanation. Still trying to get my brain around the concept. I recently got halfway through Dr. Miller's explanation of virtual photons, which is where I found that bit about particles that seem to appear out of nowhere then self-annihilate: http://www.vega.org.uk/video/programme/76

I'm still not convinced that the doppler effect of sound waves applies to photons. I need to go back to the lab and observe a hydrogen lamp and a laser through a prism. As a close-to-retirement employee of the U of Arizona, perhaps a grad student might let me observe a 3rd-semester physics lab session. (If only I could recall how I aced that advanced calculus course decades ago.

I appreciate your answer. I'll let you know when I can do the math again.