[alancalverd]

You must abandon the obsession with "limited range"

Just one question I want an answer for:
For a rotating object or God suddenly increased sun's mass,  the influence of gravity reach us with a delay .How to explain this phenomenon without the idea of a limited range extending with the speed of light c?

Easy. Delete "limted range" from your thinking and accept the experimental result that gravity appears to propagate at c. I can see what you are getting at, but your use of "limited range" is incorrect English and is confusing everyone else.

The question of "how" still baffles physicists. We have a neat mechanism in Maxwell's equations that explains the propagation of electromagnetic radiation and allows us to calculate c from static measurements, but we have insufficient evidence of gravity waves or gravitons to understand how the stuff propagates or why it sucks.

[alancalverd]

Mass cannot be created, so there is no question to answer.

E = mc². Mass is created, e.g. by pair production,  and destroyed, e.g. in nuclear fission,  every day. Big fusion reactors like the sun lose huge quantities of mass all the time, so the net gravitational field of the universe is decreasing.

[Kryptid]

E = mc2. Mass is created, e.g. by pair production,  and destroyed, e.g. in nuclear fission,  every day. Big fusion reactors like the sun lose huge quantities of mass all the time, so the net gravitational field of the universe is decreasing.

I'm pretty sure energy creates gravitational fields as well, does it not? Otherwise, it seems like you could violate the first law of thermodynamics. In principle, you should be able to convert the entire Earth's mass into energy. If that got rid of its gravitational field, then you could move a weight away from the Earth at no energy cost. Then turn the Earth's energy back into mass and let the weight fall under the influence of the newly-created gravitational field. Rinse and repeat as often as you'd like and you'd have a source of infinite energy.

[Yahya A.Sharif (OP)]

why should gravity have a limited range?

Because the gravity of the energy of a rotating object doesn't reach some places  in the universe " equals zero , is not available there , etc" and that is exactly the definition of a limited range.
Suppose there is a planet 3E^8 meters away from us , this planet rotates to create new gravity,  after 0.5 seconds its gravity range will be 1.5E^8 that means every object inside its range will be affected by its gravity and that according to the inverse squared law, and every object outside its range won't be affected by its gravity including us, we are out of range.
The limited range is not fixed its extendable and increases with time by the speed of light c.
If gravity propagate with c , and at some moment there are some places which are covered with gravity influence and some parts in the universe which are not then there is a limited range.
It is simple and obvious as this: gravity didn't reach us and available elsewhere then we are out of range and there is a limited range, gravity propagate with c then this range extends with c .
What equation is used in such case ? the equation calculate g for any given r but, if gravity didn't reach us that means g=0 for distance equals 3E^8 , making the equation invalid for this calculation.

If gravity has a limited range then it doesn't exert its influence infinitely and that what I want to say.

[Halc]

Mass cannot be created, so there is no question to answer.

E = mc². Mass is created, e.g. by pair production,  and destroyed, e.g. in nuclear fission,  every day. Big fusion reactors like the sun lose huge quantities of mass all the time, so the net gravitational field of the universe is decreasing.

You've described the transformation of energy into matter, which does not affect the mass of the system.  The created matter might have mass, but that mass was already there in the form of whatever energy was used to fuel this pair production.
Likewise, fusion and fission do the same process in reverse, again with no net change of mass.  Mass is conserved.

I say this, but then read on the wiki page for conservation of mass:

The conservation of mass only holds approximately and is considered part of a series of assumptions coming from classical mechanics. The law has to be modified to comply with the laws of quantum mechanics and special relativity under the principle of mass-energy equivalence, which states that energy and mass form one conserved quantity. For very energetic systems the conservation of mass-only is shown not to hold, as is the case in nuclear reactions and particle-antiparticle annihilation in particle physics.

The article seems to assume that energy does not constitute mass, and thus does not contribute to gravity.  I've read otherwise elsewhere.  Light, which is energy, definitely has mass since it has inertia and can push things like it does in a Crookes radiometer.
Supposedly if I pick up a rock and put it on a higher shelf, it gains potential energy and thus masses more on the higher shelf.

Rinse and repeat as often as you'd like and you'd have a source of infinite energy.

Yes, good example of the sort of contradiction that follows from energy not having gravitational mass.

[Halc]

Because the gravity of the energy of a rotating object doesn't reach some places  in the universe " equals zero , is not available there , etc" and that is exactly the definition of a limited range.

But it does reach all places of the universe. There is no finite range to the formula for force exerted.

Suppose there is a planet 3E^8 meters away from us , this planet rotates to create new gravity

There is no such thing as 'new gravity' without there being 'new mass'.

after 0.5 seconds its gravity range will be 1.5E^8 that means every object inside its range will be affected by its gravity and that according to the inverse squared law, and every object outside its range won't be affected by its gravity including us, we are out of range.

You are describing gravity waves, not gravity.  The gravity very much affects us since it was always there.

If gravity propagate with c,

But it doesn't propagate at all, so if it did, you'd be describing a different universe.
One can create a perpetual motion machine (or infinite energy generator) if gravity propagated at c.

[Colin2B]

@Halc - I don’t think Crookes radiometer is driven by light momentum transfer. It doesn’t go round in a hard vacuum, needs some air molecules.

[alancalverd]

Gravity has nothing to do with rotation. It is a function of mass only.

[alancalverd]

but that mass was already there in the form of whatever energy was used to fuel this pair production.

so you are telling me that electromagnetic radiation has a gravitational field, and therefore F≠GMm/r²?

[alancalverd]

@Halc - I don’t think Crookes radiometer is driven by light momentum transfer. It doesn’t go round in a hard vacuum, needs some air molecules.

Actually it does, but the other way round!

[Yahya A.Sharif (OP)]

Gravity has nothing to do with rotation. It is a function of mass only.

It is a function of mass and energy, rotation will increase energy and increase gravity, we will feel increment in gravity after a delay, let say we have mass m at stationary when it rotates with total kinetic energy E it will strengthen the gravity of mass by that amount , the energy of rotation is transferred by a force the source energy gravity will decrease while the object rotating gravity will increase, the increment and decrement in gravity will occur since we change the place at which the space-time is curved.i.e energy curved another place in space to strengthen its gravity and became absence from another place in space to weaken it.

[Halc]

@Halc - I don’t think Crookes radiometer is driven by light momentum transfer. It doesn’t go round in a hard vacuum, needs some air molecules.

Really?  Driven by heat then, hot on the black side.
The web sites differ.  The things are in a bulb because they need the vacuum.
Apparently they spin the other way if in air, but slowly due to the friction.

Anyway, Kryptid posted a nice refutation: Energy with no mass allows infinite energy engines.

[Bored chemist]

What do you mean by "available"?
It doesn't make sense in English to say "gravity is available everywhere".

[Yahya A.Sharif (OP)]

What do you mean by "available"?
It doesn't make sense in English to say "gravity is available everywhere".

Exist
"Gravity effect doesn't exist everywhere"

[Bored chemist]

Well, yes, it exists everywhere.
So does light (at least, in the broad sense of em radiation).

That does not say anything about it  having a "range".

[Bored chemist]

@Halc - I don’t think Crookes radiometer is driven by light momentum transfer. It doesn’t go round in a hard vacuum, needs some air molecules.

Actually it does, but the other way round!

A light mill that turns the "wrong" way is not a Crookes radiometer.

[Bill S]

As usual, I’m skimming threads, so may have missed a lot. However, to return to the OP, a few things come to mind.

If space-time is infinite ,how gravity extends to infinity?
 we know infinity is unreachable because it continues forever and no-one reach a finite point.How gravity extends to infinite distances while  infinity is unreachable? how gravity bends and curve space-time everywhere while space time end is unreachable? for gravity to bend space-time everywhere it should reach its end , how gravity bends space-time end while this end is unreachable?

Possibly the idea that gravity curves spacetime may not be helpful, here.  Spacetime is “curved” in the sense that it behaves differently from one point to another; it has a specific directionality that can be described by the same maths as would describe curvature.  It’s easy to get hung up on the “bent” bit.

If the Universe is infinite; that means no more than that it lacks a boundary, of which we could possibly be aware. 
If the Universe is homogeneous and filled with matter and radiation, then sources of gravitational attraction are everywhere, so the whole question of “how gravity bends and curve space-time everywhere” is redundant.

[Bill S]

We constantly go round in circles with anything that involves infinity.  Much of the discussion is valuable in that it provokes thought, but it seldom goes anywhere.

I have, over many years, traced most of the circles, and have, largely, “made my peace” with infinity.  I still “stir the pot” now and again; sometimes because someone introduces a perspective I’ve not thought of, and sometimes just for the hell of it.

As I see it, there are two main ways of looking at the situation; excluding philosophy and theology; these are:

1.  In keeping with the “shut up and calculate” approach to QM; one can disregard any aspect of infinity that is not amenable to mathematics.  This is quite satisfactory in that we can do all the physics, cosmology etc we need to, without going beyond this, or even having to think that there might be any “beyond”. 

2.  We can assume that the term infinity is used in, at least, two different ways. 

We live in a 3+1D Universe that is, apparently, finite, so we need only mathematical infinities for anything within our “observable” Universe.

When we try to look beyond the Universe, we probably conclude that something has always existed.  We then have a choice. We can either try to fit this “infinity” to the precepts of mathematics, and in so doing run into the endless circles; or we can shift our position on infinity.  In doing this, we have to try to avoid the restrictions of mathematics, or we just succeed in sowing the seeds of confusion. 

Of course, this is an oversimplification, but it does tend towards a degree of clarity.   

[Colin2B]

@Halc - I don’t think Crookes radiometer is driven by light momentum transfer. It doesn’t go round in a hard vacuum, needs some air molecules.

Actually it does, but the other way round!

After I had logged off I began to wonder whether it was indeed a recoil effect of em radiation leaving the surface rather than hitting the surface, if so you are right.
 I’m going to have to have a look at a few papers on this, I seem to remember a number of discussions some years ago.

[alancalverd]

Now if electromagnetic energy has a gravitational field, photons travelling through otherwise unoccupied space will tend to clump together (since gravity always sucks) , so the intensity of light received from distant stars will increase with distance, by self-focussing. And there will be stars out there that we can't see because their self-focussed beam isn't pointing in our direction.

Really?