Re: Gravity
- From: tgdenning@xxxxxxxxxxxxx
- Date: Fri, 10 Apr 2009 05:00:38 -0700 (PDT)
On Apr 9, 10:52 am, Robert Carnegie <rja.carne...@xxxxxxxxxx> wrote:
On Apr 8, 11:52 am, tgdenn...@xxxxxxxxxxxxx wrote:
On Apr 6, 8:48 pm, metspitzer <kilow...@xxxxxxxxxxx> wrote:
On Mon, 06 Apr 2009 19:04:35 -0500, metspitzer <kilow...@xxxxxxxxxxx>
wrote:
I have been watching Live Webcast of Origins Symposium at ASU.
Lawrence Krauss just said that gravity pushes.
I saw a Universe show on the History channel and Michio Kaku said that
space was actually pushing you into your chair.
Who is right?
Lawrence Krauss said that gravity pulls
typo or just brain fart.
Is this like the other thread with Alan Watts?
Actually, the pushing has a bit more stature since you could argue
proximate cause; we are obliged to conform to the space-time metric,
and the causal relationship between the nature of the local space
around the chair and the 'mass' of the earth is one step removed, and,
to my mind, not completely clear.
Of course, Alan Watts might not make that distinction....
How about: your chair is pushing you through space? 'Cause if you
just obeyed gravity you'd be falling down.
I think because it's really spacetime, it probably can't really be
expressed in terms of space only. But try this - space is continually
sucked in by the Earth and swallowed. When you sit down, the chair
interrupts the fall that you.were falling together with your space.
Or think of a river (maybe a waterfall? perhaps I can leave that
out), and a boat floating in the river. The boat strikes a rock in
the middle of the river, so it stops relative to the rock, but in a
way it is now moving through the water, except that really it is the
water that is moving. The water is the space, the boat is you, the
rock is the chair.
Gravity is the effect of mass changing the definition of "straight
line" - "geodesic" in space nearby, and in theory out to the end of
the universe, but only at the speed of light. So in a sense, the
planets orbiting the Sun are moving along "straight lines" in
spacetime, and not being pulled around the Sun.
The problem, as with the thread about curved path of light, is both
that we think metaphorically, in an attempt to relate these things to
our physical experience, and that different theories use different
metaphors or physical models, and people tend to mix them all together
inappropriately.
I was trying to say that *in the abstract*, 'being pushed' represents
the individual's POV, while 'pulling' might make sense from the
perspective of the 'mass' that is 'causing' the nature of the space-
time metric. Imperfect analogy: A fish trapped in a net feels the net
pushing on it, a human in the same situation would know that someone
was 'pulling' them because he could meta-perceive the situation.
If you change the situation, and change the metaphor to be less
abstract: Falling freely, you might well experience a tidal effect,
such that you would feel that you are being pulled.
And of course you can think of various physiological and psychological
outcomes in various real situations---if you are pressed up against a
rock by moving water, you may feel the pressure of the water more or
the 'reaction force' of the rock more, depending on the geometry.
-tg
.
- References:
- Gravity
- From: metspitzer
- Re: Gravity
- From: metspitzer
- Re: Gravity
- From: tgdenning
- Re: Gravity
- From: Robert Carnegie
- Gravity
- Prev by Date: Re: Texas: Board Set to Vote on Challenge to Evolution
- Next by Date: Re: Statistics of Fingerprints
- Previous by thread: Re: Gravity
- Next by thread: Re: Gravity
- Index(es):
Relevant Pages
|
Loading
