Re: Dark matter/energy - is it real?

"Tue Sorensen" <sorensonian@xxxxxxxxx> wrote in message
news:1144377801.024816.229310@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Wayne Throop wrote:
It's sort of like the domino theory, only with physics. The whole thing
unravels, unless a photon moves a star. And physicists find this sort
of
argument persuasive. They don't like everything to unravel, especially
not the parts they are really quite sure of, like conservation laws.
Nobody has ever made money betting against basic conservation laws.
Well OK, maybe somebody won out with some of the little ones, like
parity conservationj or baryone number. But not the really big ones,
like energy and momentum. The fact that you don't find this sort of
argument convincing is not a flaw in physicists.

Well, one never knows. Not all theoretical suppositions can stand the
test of time.

Well, if you want to bet against conservation of momentum and energy, I
guess that's your right, but don't expect anyone to take you seriously.

that photon must act on the source
of the gravity in an equal and opposite way. If you don't want to
call that "having gravity", then you're just playing silly word games.
Because you *do* call that "having gravity" when any other particle does
it; to exclude photons is silly. Silly word games.

But photons are massless

(http://math.ucr.edu/home/baez/physics/ParticleAndNuclear/photon_mass.html).
This makes a *every* difference. Energy and matter, as well as being
equivalent, are polar opposites. Each have their own laws of causality.

As far as I can tell, now you're just makin' things up.

: So the fact that light follows the curvature of space is proof that
: light has gravity? I still don't see it.

But light doesn't follow the "curvature of space". Nor does anything
else. It follows the curvature of spacetime, which is something
quite different. OK, so it's "subtly different". The point is,
"following the curvature of space (or spacetime)" doesn't absolve you
from conserving momentum, and doesn't absolve you from interacting with
the spacetime you are following the curve of. You can't just take one
half of something (ie, "light follows spacetime curvature"), on vaguely
understood theoretical grounds, and totally ignore the other half, (ie,
"spacetime curvature is affected by light"),

Affected? Even if light does have gravity, the effect amounts to a
lotta nothing. It's that small.

So? It's still there. Get energetic enough photons, or get enough photons,
and it will become noticeable. (Somewhere around 1.36E52 Watts worth of 'em
oughta do it.) The momentum of a single air molecule isn't that great, but
trillions of them can move ships.

just because you understand that part of the theory less.

I certainly trust it less.

Why?

Because just chanting "space curvature
space curvature space space curvature curvature" like latter day airport
krishnas doesn't mean that you can simply ignore where the spacetime
distortion comes from in the first place. Which is, essentially,
energy.
Not mass, energy.

Oh?

Really.

Yeah??

It is.

How? When? You mean back around the big bang?

Yes, but now, too. Gravity is tied to the stress energy tensor. The stress
energy tensor describes energy and momentum flux through spacetime. Usually,
large masses, which are after all essentially enormous agglomerations of
energy, dominate, and thus it looks like gravity is tied to mass. But
photons, despite lacking mass, still have energy and momentum, so their
presence in spacetime causes gravity just like the bigger, more impressive
agglomerations of energy and mometum do.

That's what the theory says, whether
you like it or not. And you can't just take the parts you like and
ignore the rest, and then conclude that proves there's something fishy
about the theory. The only thing fishy is that you fished out the
bits you like and ignored the rest.

To reinvent the rules, first you must break them...

And if the rules don't need reinventing?

: But the influence of an object's gravity lessens the passing light's
: momentum, right? That's how you figure light's got gravity?

Not necessarily lessens it. Changes it. Momentum is a vector.

And what's a vector? Don't worry, I'll be here all night...

vec·tor (vek'tr)
n.
1. Mathematics.
a. A quantity, such as velocity, completely specified by a magnitude and
a direction.
b. A one-dimensional array.

And this is no different
for light than for any other thing passing by; indeed, other than
you don't like it, I see no reason why it *shouldn't* be the same for
light; what makes light so special that it doesn't need to provide an
equal and opposite reaction like everything else does? Just because it
has no mass?

Yes, pretty much.

That just Doesn't Make Sense.

See, physicists say "light is just like everything else; it obeys
all the conservation rules". You say "light is special, and deserves
a waiver for its conservation duties".

No, I simply suggest that there may be a different answer to how it
deals with the energy imbalance. Light is after all superpositional,
which is a very strange phenomenon.

There is no good reason to assume that. It would involve Everything Falling
Down if it were true. And yet, our current understanding of how light works
actually holds up very well.

: A little bit deflected, perhaps. But all light isn't pulled into all
: gravity wells.

You say that as if it were significant somehow.

It is! It means some light defies spacetime curvature, going its own
ways instead. It means that there must be some threshold values to when
how much light is pulled into a given strong gravity well. It's all got
to do with probabilities, no doubt, but it's certainly very mysterious.
If you don't agree, would you be so good as to explain it?

Except that it doesn't, and there aren't. Light is affected by gravity just
like everything else. All of it, without exception. You just don't notice it
most of the time, because you're used to living with relatively weak
gravitational fields, and light goes really freakin' fast.
I believe there is confusion as to terminology. "Pulled into gravity wells"
is not at all precise. No light is ever *captured* by a gravity well smaller
than a black hole, because the definition of a black hole is that it has
such a high escape velocity that light can't get out. *All* light, however,
is bent somewhat by *all* gravitational fields.

: Going against gravity and all.

Nope, obey it just like sheep they do, same as all the other particles,
cosmic rays and ping-pong balls and meteors and planets and stars alike.

But some photons go from the Eath to the Moon. That's kinda against
gravity, isn't it?

And balls go up when you throw them that way. That's kinda against gravity,
isn't it?
Well, sure, they're moving in a direction opposite to the acceleration
applied by gravity, but they loose energy all the way up, and eventually
fall back down if they don't have escape velocity. Similarly, those photons
will be losing energy all the way up Earth's gravity well.

-l.
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