Expanding Universe?

I have had some questions about this since I heard of it. We measure large distances by the red shift of light to lower energies. But we know that gravity has the same effect. So the presence of large undetected quantities of ordinary matter should make distance galaxies look farther away. When I asked a physics professor about this years ago, he replied that physicists are human, and have fads like everybody else.

And this morning I was reminded by a report on NPR on this Nobel prize that the farther away something is, the older it is. If the farther away something is the faster it is going, doesn't that mean that the longer ago it was, the faster? So maybe the universe is really slowing?

If there are any physicists out there who can explain things to us non-experts, please let us know.


www.msnbc.msn.com

By KARL RITTER, MALCOLM RITTER
updated 10/4/2011 3:27:24 PM ET

NEW YORK — Three U.S.-born scientists won the Nobel Prize in physics Tuesday for discovering that the universe is expanding at an accelerating pace, a stunning revelation that suggests the cosmos could be headed for a colder, bleaker future, nearly devoid of light.

In 1998, Saul Perlmutter, Brian Schmidt and Adam Riess presented findings that overturned the conventional idea that the expansion was slowing 13.7 billion years after the big bang.

[...]

Working in two teams, with Perlmutter heading one, they had raced to measure the universe's expansion by analyzing light from dozens of exploding stars called supernovas. They found the light was weaker than expected, signaling that the expansion of the universe was accelerating.

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One consequence of the finding is that in a trillion years, galaxies will be spread apart from each other by more than the current size of the universe, he said. And the ever-greater expansion rate means the light from one galaxy will no longer be visible from another as it is today, he said.

[...]

But Robert Kirshner, a Harvard astronomer who was part of the team that included his former students Schmidt and Riess, said scientists don't know enough about dark energy to predict what will happen to the universe hundreds of billions of years from now.

One possibility is that the expansion will continue to accelerate, he said, "sort of like compound interest gone mad." It could even speed up so much that not only will galaxies fly apart from each other, but "stuff will really rip apart," even planets and atoms, he said. That's called the "big rip," "and I hope that's not our fate."

On the other hand, Kirshner said, the expansion could halt and go into reverse, so the universe collapses back into itself, a fate sometimes called the "big crunch."

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