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...A Simple Question About Gravity...Bet You Can't Answer!

...A Simple Question About Gravity...Bet You Can't Answer! - Physics Forum

...A Simple Question About Gravity...Bet You Can't Answer! - Physics Forum. Discuss and ask physics questions, kinematics and other physics problems.

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Old 02-05-2006, 05:27 PM
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Default ...A Simple Question About Gravity...Bet You Can't Answer!

jonathan wrote:

General relativity models gravity as a *local* property of space.
Earth's orbital path isn't determined directly by the distant Sun, but
rather is determined by the differential geometry of the space right
here, where Earth is. And the spatial geometry here is a function of
the spatial geometry just infinitesimally closer to the Sun, which is
yet again determined by the properties of space just infinitesimally
closer, and so on. There is no action at a distance in field theories.

-Mark Martin

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Old 02-06-2006, 09:03 PM
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Default ...A Simple Question About Gravity...Bet You Can't Answer!

jonathan wrote:

Yes, gravitons are "plausibly" analagous to photons. In fact, there
is some formal similarity between GR & EM. There are, for example,
"electric" and "magnetic" components to gravitational waves. (Though
gravity waves have yet to be detected.) A strong difference between GR
& EM is that, while in EM the photon is definitely a carrier of force,
the graviton's role could be less direct. The graviton isn't necessary
for gravity to work; GR still models gravity as local spatial geometry.
The graviton could just be the unit excitation of the gravitational
field, much as the photon is in the EM field. Experimentally either
verifying or excluding the existence of gravitons would then be mainly
to tell theorists whether or not they're still on the right track.

But even if the graviton turns out to be a direct carrier of force,
it still doesn't amount to FTL action at a distance. The interaction
would still be delayed, and would be local.

Well... "science" isn't about anything in particular. People ask
questions, and if they are so inclined they go about answering the
question scientifically. If you personally are asking "How did we get
here?", then it's possible that work on gravitation is irrelevant to
your interests. It is on the other hand of interest to others who ask
"What does it mean when things fall down?"

But how can reductionist theories of Nature be connected with life,
i.e., biology?

First, it is possible to at least determine what natural conditions
are necessary for what we call "life" to thrive, or even to exist at
all. It's possible right here on Earth to find a variety of
circumstances, some of which are conducive to living things, and others
which clearly preclude it. The molten interior of the planet, for
example, is 100% hostile to living things. So by determining what
conditions must at least in principle be possible in order for living
things to go about their business can be valuable information. If the
universe were absoluetly everywhere inhospitable to organisms, then we
wouldn't be here to inquire of our own origins. So a cosmoligist can
know right from the get-go that physical parameters must be within
narrow tolerances such that we can even be here at all.

Second, not every question must be explicitly about so-called
"life". There are many people, all asking their own questions. There's
room for all. In my own family there is room for both extremes. I tend
towards studying physics, whereas my wife is a professional biologist.
She knows very little about physics, and what I know of her specialty
amounts to what she tells me in idle conversation. But we get along
quite lovingly.

-Mark Martin

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