# The Naked Scientists Forum

### Author Topic: Could gravity be everything expanding outwards?  (Read 3090 times)

#### chris

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##### Could gravity be everything expanding outwards?
« on: 12/04/2008 22:54:44 »
I was asked by someone the other day if I was acquainted with a "scientist" called ?McCloughlin who, the caller claimed, suggested that gravity as an attractive force does not exist and is instead a manifestation of everything continously expanding. That is, an apple falls to the floor because the floor expands up to meet the apple.

Has anyone ever some across this claim? It's hard to develop a sensible argument when one doesn't know about the "theory" to begin with.

Chris

#### lyner

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##### Could gravity be everything expanding outwards?
« Reply #1 on: 12/04/2008 23:26:09 »
Geometry could go a bit wild if that theory applied, I think. Which bits of the Universe would be expanding faster than which bits?

#### JP

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##### Could gravity be everything expanding outwards?
« Reply #2 on: 13/04/2008 02:52:47 »
I've seen this mentioned before, but I don't know who McCloughlin is.  Generally people assume that since something falling towards the earth has an acceleration of ~9.8 m/s^2 downwards, that a good model would be to have the earth expanding outwards with an acceleration of 9.8 m/s^2.

The problem with the expansion theory is written up well in this link:

http://www.mathpages.com/home/kmath077/kmath077.htm

Essentially, you have to keep adding things to your theory until you end up with general relativity:

(1) If everything is expanding equally, the earth is expanding towards the apple and the apple towards the earth, but the distance separating them is expanding as well, so they never appear to get closer together.

(2) If only massive objects expand, and not space between them then everything would quickly be squashed together into one big lump, so this can't be the case.

(3) The big problem, however, is that expansion-as-gravity doesn't explain how gravity can change the direction of an object's motion.  Expansion was introduced so that there are no forces-at-a-distance tugging on masses, so you can't change the direction of a particle's velocity.  Therefore, you can't explain objects in orbit, since they're clearly traveling in opposite directions when they're on opposite sides of the earth.  If you try to get around this by assuming there is some action at a distance due to expansion, you've introduced the idea of a gravitational field (and it turns out to be equivalent to describing gravity as warping of space-time, which is general relativity).

#### lyner

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##### Could gravity be everything expanding outwards?
« Reply #3 on: 13/04/2008 13:12:38 »
And how does expansion explain circular orbits, hey hey?

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##### Could gravity be everything expanding outwards?
« Reply #3 on: 13/04/2008 13:12:38 »