# Naked Science Forum

## Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Yahya A.Sharif on 26/05/2019 19:20:30

Title: How does gravity exert its influence infinitely?
Post by: Yahya A.Sharif on 26/05/2019 19:20:30
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?
Title: Re: How does gravity exert its influence infinitely?
Post by: Halc on 26/05/2019 19:37:18
for gravity to bend space-time everywhere it should reach its end
There is no end to F = GMm/r², so there is no such end to reach.
You seem to be treating infinity as a number, or treating gravity as something that moves at a speed, which it doesn't.  Gravity waves do, and thus gravity waves reach only a finite distance.
Title: Re: How does gravity exert its influence infinitely?
Post by: Yahya A.Sharif on 26/05/2019 19:52:23
for gravity to bend space-time everywhere it should reach its end
There is no end to F = GMm/r², so there is no such end to reach.
You seem to be treating infinity as a number, or treating gravity as something that moves at a speed, which it doesn't.  Gravity waves do, and thus gravity waves reach only a finite distance.
Still my question is not answered . does force between two masses placed anywhere in space exists ?
it means for force to exist gravity should be everywhere as well .
Space-time curvature happens due to mass existence , is mass existence effect "curvature"  everywhere ?
how this effect could reach infinity" infinity is not an end or point but something continues forever" while infinity is unreachable?

Title: Re: How does gravity exert its influence infinitely?
Post by: Bored chemist on 26/05/2019 19:54:39
Still my question is not answered .
Yes it was.
Title: Re: How does gravity exert its influence infinitely?
Post by: Yahya A.Sharif on 26/05/2019 19:57:05
Still my question is not answered .
Yes it was.
A mass started to bend the space time around it at time, is it physical that this curvature happens at the same time everywhere?
Title: Re: How does gravity exert its influence infinitely?
Post by: Halc on 26/05/2019 22:02:12
Still my question is not answered . does force between two masses placed anywhere in space exists ?
You can't 'place' mass in space.  There's no way to create it or destroy it.  So yes, the force exists everywhere, at any distance, even if far further away than can be identified as being from a specific mass.

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Space-time curvature happens due to mass existence , is mass existence effect "curvature"  everywhere ?
Yes, of course.  There is nowhere where there isn't mass existing at some distance, even if you choose a spot where there isn't particularly much of it locally.

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how this effect could reach infinity" infinity is not an end or point but something continues forever" while infinity is unreachable?
I don't see what is 'unreachable' about a field that doesn't get to zero at some finite distance.

A mass started to bend the space time around it at time
For it to have 'started to' bend spacetime, the mass would need to have 'started', which I suppose might be how you describe things at the big bang moment when all was local.  But otherwise, you can't 'start' a mass, and expect this new mass to have an effect at infinite (or even finite distance) in a short time.  Mass cannot be 'started', so that doesn't work.
Title: Re: How does gravity exert its influence infinitely?
Post by: Yahya A.Sharif on 27/05/2019 10:57:55
Hi Halc,
Thanks for your replies,
What I can't understand is a mass has its effect "space time  curvature" everywhere at an instance is not physical
Also there should be a starting moment when mass started to bend space-time it can't be infinitely in the past.
How mass bend space-time infinitely while this infinity in fact is not fixed and continues forever?
If an object is at constant speed it will move forever never reaching infinity, if I want to move an object from point A to point B I have to go through several points to reach point B this what physics says I can't let it jump from point A to point B the same for gravity it can't jump at an instance to infinity"even infinity can't be reached" so how space-time curvature started at a moment and at instance spread everywhere?

Mass cannot be 'started', so that doesn't work.
What about a rotating object with a torque? it start to have energy inside it and mass and energy are interchangeable so we will then have mass started.We didn't simply place energy from an environment to the mass we transferred energy from form to another so we indeed started new mass with its own gravity.
Title: Re: How does gravity exert its influence infinitely?
Post by: Bored chemist on 27/05/2019 11:07:38
What about a rotating object with a torque?
It has the same mass as it started.

There is some validity to you point.
If God suddenly decided to double the mass of the Sun, nothing on Earth would notice for about 8 minutes and it would be about 5 hours before any effect was observed by Pluto.

However there are two issues that stop this being a contradiction of known physics.

No known process could suddenly double the mass of the Sun without bringing the mass in from somewhere else. (That's why I invoked a God to do it)
The range of the effect would still be infinite- it would just take a while to get there.
There isn't anything that would stop the effect of the change in gravity- so it would go on for ever.
It is infinite.

Title: Re: How does gravity exert its influence infinitely?
Post by: Bored chemist on 27/05/2019 11:09:07
there should be a starting moment when mass started to bend space-time it can't be infinitely in the past.
Yes, the big bang.
And everything was in the same place at the same time, so there was no need for any effect to travel.
Title: Re: How does gravity exert its influence infinitely?
Post by: alancalverd on 27/05/2019 11:19:44
As far as we know, the gravitational equation appears to be universally true. We also know that a gravitational field bends the path of electromagnetic radiation to the extent that we can observe the effect of black holes.

Now consider a finite part of an infinite universe, populated by various massive particles from atoms to galaxies. If we make this sample large enough (and there is no limit since it is a sample of an infinite universe) it will contain enough mass to appear from outside to be a large black hole with an event horizon, which no information can cross.

We have thus defined a "real" infinity, comprised of an infinite number of mutually nonobservable "virtual" infinities.

This model has characteristics both of Hoyle's "continuous creation" universe, as seen from inside, and the Big Bang hypothesis which allows for the spontaneous creation and expansion of new, virtually infinite, mini-universes, as seen from outside.
Title: Re: How does gravity exert its influence infinitely?
Post by: Yahya A.Sharif on 27/05/2019 11:39:06
It has the same mass as it started.
But not the same gravity

If God suddenly decided to double the mass of the Sun, nothing on Earth would notice for about 8 minutes and it would be about 5 hours before any effect was observed by Pluto.
Then gravity is not everywhere since the big bang is the start of every mass every mass effect still didn't reach infinite distances. If its effect didn't reach there then  gravity doesn't exist.

Title: Re: How does gravity exert its influence infinitely?
Post by: Bored chemist on 27/05/2019 11:43:37
It has the same mass as it started.
But not the same gravity

If God suddenly decided to double the mass of the Sun, nothing on Earth would notice for about 8 minutes and it would be about 5 hours before any effect was observed by Pluto.
Then gravity is not everywhere since the big bang is the start of every mass every mass effect still didn't reach infinite distances. If its effect didn't reach there then  gravity doesn't exist.

There are events in the universe from which the light has yet to reach us.
Are you saying that means those events don't exist?
Or are you saying that light doesn't exist?
Or what?
You really need to make yourself clear.
So far there's is nothing new in what you have said.
Title: Re: How does gravity exert its influence infinitely?
Post by: Yahya A.Sharif on 27/05/2019 11:47:22
As far as we know, the gravitational equation appears to be universally true.
The equation is not necessarily to validate the theory.
Title: Re: A question about gravity
Post by: jeffreyH on 27/05/2019 12:24:58
Was there gravity before the big bang? Yes. Why? Because it was combined with the other forces. Gravity doesn't suddenly spring into existence out of nowhere. It has energy and energy is conserved.
Title: Re: How does gravity exert its influence infinitely?
Post by: Yahya A.Sharif on 27/05/2019 12:48:39

No known process could suddenly double the mass of the Sun without bringing the mass in from somewhere else.

But it could double its kinetic energy for a rotating object using a force in fact we didn't just simply take the energy and placed it into the object we transferred it using force the previous gravity will weaken and new gravity will appear
Title: Re: How does gravity exert its influence infinitely?
Post by: Bored chemist on 27/05/2019 13:10:07
Cut to the chase.
"How does gravity exert its influence infinitely?"
How could it not do so?
What would stop it?
Title: Re: How does gravity exert its influence infinitely?
Post by: Bored chemist on 27/05/2019 13:12:08
But it could double its kinetic energy for a rotating object using a force
That force would have to be exerted by an object which had mass or by, for example, EM radiation emitted by an object with mass.
In either case, there's a movement of mass, not a creation of mass.
Title: Re: How does gravity exert its influence infinitely?
Post by: Halc on 27/05/2019 13:29:09
Hi Halc,
Thanks for your replies,
What I can't understand is a mass has its effect "space time  curvature" everywhere at an instance is not physical
It's about as physical as it can get.  That's why we call this 'physics'.
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Also there should be a starting moment when mass started to bend space-time
That would violate the 3rd law of thermodynamics.  So no.

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If an object is at constant speed it will move forever never reaching infinity
Again, you treat infinity like a number, a sort of marker that an object might hope to reach.  That aside, an object at constant speed will go no further than some finite distance.  Two rocks sufficiently far apart that are moving 'forever' at some constant speed will never in fact reach each other.  If they're close enough, they will.

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if I want to move an object from point A to point B I have to go through several points to reach point B this what physics says
That's sort of what mathematics says.  Punctuation is also your friend.  Try it sometime.
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I can't let it jump from point A to point B the same for gravity
Gravity isn't an object.  It doesn't travel.
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so how space-time curvature started at a moment
It doesn't 'start at a moment', which again would violate the 3rd law.

Mass cannot be 'started', so that doesn't work.
What about a rotating object with a torque?[/quote]An object doesn't need to rotate to apply torque, and a rotating object doesn't necessarily have torque.  That said, what about it?  Torque does not affect gravity.  Mass does.

[/quote] it start to have energy inside it and mass and energy are interchangeable so we will then have mass started.[/quote]No mass was 'started'.  You can add mass to A by moving it from B, but that is still a net of zero.

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We didn't simply place energy from an environment to the mass we transferred energy from form to another so we indeed started new mass with its own gravity.
Without punctuation, I cannot tell what you're trying to describe, but it cannot be a valid description of the 'starting' of new mass.  What are you doing to the object that doesn't involve it getting new energy from outside?
Title: Re: How does gravity exert its influence infinitely?
Post by: Halc on 27/05/2019 13:40:16
Quote from: Bored chemist
No known process could suddenly double the mass of the Sun without bringing the mass in from somewhere else.
But it could double its kinetic energy for a rotating object using a force in fact we didn't just simply take the energy and placed it into the object we transferred it using force the previous gravity will weaken and new gravity will appear
Very little of the mass of the sun is manifested in its kinetic energy, so to double that would have almost no effect on its mass. The only way to double its kinetic energy is to take that energy from somewhere else, possibly itself.
I can double the kinetic energy of my car by coasting down a hill.  This takes potential energy away from the car and changes that into kinetic energy.  That's a net mass change of zero, so the car exerts no more or less gravitational pull than before.
Title: Re: How does gravity exert its influence infinitely?
Post by: Yahya A.Sharif on 27/05/2019 13:51:36
That's a net mass change of zero, so the car exerts no more or less gravitational pull than before.
But the place in which the space-time is curved is different. An example is a battery and an object rotating on an electric motor the gravitational field of the battery will decrease while the gravitational field of the object will increase.
Title: Re: How does gravity exert its influence infinitely?
Post by: Bored chemist on 27/05/2019 13:56:08
That's a net mass change of zero, so the car exerts no more or less gravitational pull than before.
But the place in which the space-time is curved is different. An example is a battery and an object rotating on an electric motor the gravitational field of the battery will decrease while the gravitational field of the object will increase.
And you would get the same effect if an ant walked from one place to another; from the battery to the motor.
Some mass would move.
So what?
Title: Re: How does gravity exert its influence infinitely?
Post by: Halc on 27/05/2019 14:09:51
Quote from: Halc
That's a net mass change of zero, so the car exerts no more or less gravitational pull than before.
But the place in which the space-time is curved is different.
Yes, that has changed.  The car isn't where it was.
It changes the shape of the gravitational field, but since there was a reaction mass involved, there was an equal change in the opposite direction.  If my car goes north downhill, the Earth (the reaction mass) moves south a bit, resulting in no net change as to where our combined gravitational field is centered.

The field has indeed changed due this rearrangement of the masses involved, and that change is propagated at lightspeed via gravity waves.  Those waves will never reach sufficiently distant objects.

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An example is a battery and an object rotating on an electric motor the gravitational field of the battery will decrease while the gravitational field of the object will increase.
Yes, the battery is giving up its mass to something else (the motor) which in turn probably gives it up to yet something else like kinetic energy of the spinning object.  Total energy/mass is always conserved.
Title: Re: How does gravity exert its influence infinitely?
Post by: Yahya A.Sharif on 27/05/2019 14:16:31
The field has indeed changed due this rearrangement of the masses involved, and that change is propagated at lightspeed via gravity waves.
Gravitational waves is about an accelerated mass however in such case the gravity of the object will increase and strengthen but not in a form of waves.This about mass increment not accelerated mass.
Title: Re: How does gravity exert its influence infinitely?
Post by: alancalverd on 27/05/2019 15:30:46
As far as we know, the gravitational equation appears to be universally true.
The equation is not necessarily to validate the theory.
On the contrary, theories are validated by prediction, and prediction in physics requires an equation.
Title: Re: How does gravity exert its influence infinitely?
Post by: Halc on 27/05/2019 15:39:06
Gravitational waves is about an accelerated mass however in such case the gravity of the object will increase and strengthen
Earth is accelerating all the time, yet its mass is not increasing due to that. But the motion does indeed generate waves, and those waves do carry energy away, so in that sense, the Earth/sun system loses (not gains) mass at a pace of about 200 watts.
Title: Re: How does gravity exert its influence infinitely?
Post by: Yahya A.Sharif on 27/05/2019 16:00:00
As far as we know, the gravitational equation appears to be universally true.
The equation is not necessarily to validate the theory.
On the contrary, theories are validated by prediction, and prediction in physics requires an equation.
All tests for the equation are within gravity influence but not at infinite distances.The equation might be valid within gravity influence but wrong beyond that.
Title: Re: How does gravity exert its influence infinitely?
Post by: Bored chemist on 27/05/2019 16:49:00
The equation might be valid within gravity influence but wrong beyond that.
And you might turn into a unicorn tomorrow.
But that's not a good reason to assume that you will.
Title: Re: How does gravity exert its influence infinitely?
Post by: alancalverd on 27/05/2019 17:46:17
As r → ∞, F → 0, so the equation is an operational definition of infinity.
Title: Re: How does gravity exert its influence infinitely?
Post by: Yahya A.Sharif on 27/05/2019 18:16:48
As r → ∞, F → 0, so the equation is an operational definition of infinity.
Mathematically the equation is true, in reality it is not.It means it is true only if the influence reached infinity.
I don't want to involve in my personal ideas here , but suppose gravity influence decreases by the speed of light c and drops to zero beyond its range , then we would have gravity at earth's surface equals 9.8 m/s/s and a changeable amount "at the edge of its range " "decreasing" in such case the equation would be valid within its range and we can take double integration from zero to the edge and from the edge to the earth surface to calculate for instance escape velocity.In such case all current observations will be true using a concept of limited range.
The gravitational equation could be modified in order to be valid everywhere or it could be valid everywhere except beyond the gravity influence.
Title: Re: How does gravity exert its influence infinitely?
Post by: Bored chemist on 27/05/2019 20:02:42
suppose gravity influence decreases ... and drops to zero beyond its range

Then you need to answer the question I asked earlier.

Cut to the chase.
"How does gravity exert its influence infinitely?"
How could it not do so?
What would stop it?
Title: Re: How does gravity exert its influence infinitely?
Post by: alancalverd on 27/05/2019 21:46:31
Mathematically the equation is true, in reality it is not.
Any statement taken as a definition cannot be false. I defined infinity as the distance at which F = 0.

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but suppose gravity influence decreases by the speed of light c and drops to zero beyond its range ,
This phrase is meaningless. Speed is not equivalent to distance. "Decreases by the speed of light" has no meaning.

If there is a finite range for gravitation (and why should there be? all other inverse square forces are unbounded), what determines the cutoff point?
Title: Re: How does gravity exert its influence infinitely?
Post by: Yahya A.Sharif on 28/05/2019 08:57:33
I defined infinity as the distance at which F = 0.
At F=0 the equation fails to determine the distance " undefined"

all other inverse square forces are unbounded
The same idea for other inverse square forces is applied as for gravity.

what determines the cutoff point?
The time since the gravitational field comes to existence:
F=GMm/c²t²
ct is the distance from mass center to the cutoff point where t is the time elapsed.

Title: Re: How does gravity exert its influence infinitely?
Post by: Yahya A.Sharif on 28/05/2019 09:01:39
Just one question I want an answer for:
Why in case of a rotating object or God suddenly increased sun's mass, why the influence of gravity reach us with a delay? How to explain this phenomenon only with the idea of a limited range extending with the speed of light c?

Title: Re: How does gravity exert its influence infinitely?
Post by: Bored chemist on 28/05/2019 09:11:29
you need to answer the question I asked earlier.
Title: Re: How does gravity exert its influence infinitely?
Post by: alancalverd on 28/05/2019 10:17:35
You must abandon the obsession with "limited range", for which there is no evidence or mechanism. The position vector for a pulse travelling at velocity c at time t is obviously ct but there is no limit to t and in an empty universe there is no curvature to c.

What makes gravity unique is its unipolar suck, and what makes it interesting is its apparent propagation speed c. Adding imaginary and wholly unobserved properties like limited range doesn't improve any of our models.
Title: Re: How does gravity exert its influence infinitely?
Post by: alancalverd on 28/05/2019 10:23:18
Quote from: alancalverd on Yesterday at 21:46:31
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I defined infinity as the distance at which F = 0.

At F=0 the equation fails to determine the distance " undefined"

For every value of F, you can find a smaller value by increasing r. That is how we describe continuum infinities. If F = 0 then r must be larger than any distance you can measure or imagine, so "determine the distance" is meaningless.
Title: Re: How does gravity exert its influence infinitely?
Post by: Yahya A.Sharif on 28/05/2019 10:28:14
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?
Title: Re: How does gravity exert its influence infinitely?
Post by: Yahya A.Sharif on 28/05/2019 10:30:46
If gravity is everywhere, as soon as mass increased or an object rotates gravity of the mass or energy should be available everywhere at an instance and never delay.
What equation is used in such case? giving the idea gravity will equal zero not for infinity but for real number distances, how the equation works then ?
Title: Re: How does gravity exert its influence infinitely?
Post by: Bored chemist on 28/05/2019 10:42:28
If gravity is everywhere, as soon as mass increased or an object rotates gravity of the mass or energy should be available everywhere at an instance and never delay.
Nonsense.
The best available evidence suggests that gravity and light travel at the same speed. (It's much easier to turn a light on than to suddenly create mass).
So let's see what happens if we pretend that your view is right, and apply it to light.

"If gravity light is everywhere, as soon as mass increased or an object rotates a bulb is turned on gravity light of the mass or energy bulb should be available everywhere at an instance and never delay."

It makes no sense with light, and it makes no sense with gravity
Title: Re: How does gravity exert its influence infinitely?
Post by: Bored chemist on 28/05/2019 10:43:21
you need to answer the question I asked earlier.

Title: Re: How does gravity exert its influence infinitely?
Post by: Yahya A.Sharif on 28/05/2019 11:02:10
"If gravity light is everywhere, as soon as mass increased or an object rotates a bulb is turned on gravity light of the mass or energy bulb should be available everywhere at an instance and never delay."

It makes no sense with light, and it makes no sense with gravity
It is not my idea, it is the current view that gravity is available everywhere but you answered:
It makes no sense with gravity
I still ask my question:
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?
How the equation works in such case? we have masses and distance between them but the force equals zero for real number values of distance

Title: Re: How does gravity exert its influence infinitely?
Post by: Colin2B on 28/05/2019 11:57:17
"If gravity light is everywhere, as soon as mass increased or an object rotates a bulb is turned on gravity light of the mass or energy bulb should be available everywhere at an instance and never delay."

It makes no sense with light, and it makes no sense with gravity
It is not my idea, it is the current view that gravity is available everywhere but you answered:
It makes no sense with gravity
As @Bored chemist  answered, there is no reason to suggest that a change in gravity propagates instantaneously ie without delay.

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?
This has been answered by @alancalverd  who explained that there is no reason to introduce the idea of limited range.
Light propagates at c but has no limited range, why should gravity have a limited range?
Title: Re: How does gravity exert its influence infinitely?
Post by: Bored chemist on 28/05/2019 12:16:26
I still ask my question:
Why?
It is not my idea, it is the current view that gravity is available everywhere
What do you mean by "available"?
It doesn't make sense in English to say "gravity is available everywhere".
Title: Re: How does gravity exert its influence infinitely?
Post by: alancalverd on 28/05/2019 12:36:01
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.
Title: Re: How does gravity exert its influence infinitely?
Post by: Halc on 28/05/2019 12:41:09
If gravity is everywhere, as soon as mass increased or an object rotates gravity of the mass or energy should be available everywhere at an instance and never delay.
Mass cannot be created, so there is no question to answer.  If a god is creating mass, then you have to consult the laws of physics for a universe that contains a god who creates mass. This isn't that universe.
Title: Re: How does gravity exert its influence infinitely?
Post by: Halc on 28/05/2019 12:49:07
The best available evidence suggests that gravity and light travel at the same speed. (It's much easier to turn a light on than to suddenly create mass).It makes no sense with light, and it makes no sense with gravity
Gravity doesn't 'travel'.  Since mass cannot be created, there can be no net change to the field, only a different arrangement of existing mass (not even a different position of it) that has no net effect that needs to propagate long distances.  Short distances, sure.  I am attracted differently to a pair of masses aligned with me than the same pair side-by-side, which is why planetary alignment increases the chances of earthquakes.  At a distance, that alignment difference has negligible effect, and that difference (not the gravity itself, but the change to it) needs to propagate at light speed, and thus has finite range.  Yes, we have devices that measure such alignment difference at great distances, but not too great.
Title: Re: How does gravity exert its influence infinitely?
Post by: Halc on 28/05/2019 13:00:31
Things that propagate at c (light for instance) do have a limited range in that it can never reach an object which is under continuous acceleration away from it.  So for instance, if I was in a ship accelerating forever at 1G, light from about a lightyear behind it would never reach it.  Gravity from an object would be felt since it doesn't propagate at c, but changes to that field do propagate at c, so those changes would not be felt at the ship.

Objects about 15 BLY away are accelerating enough that no light can reach between us in either direction ever.  That's a finite distance of sorts.  Gravity waves can similarly never reach that far, but the gravitational field is already there and no time is required for the force of the Sun's gravity to be exerted on those distant objects and v-v.
Title: Re: How does gravity exert its influence infinitely?
Post by: alancalverd on 28/05/2019 13:53:47
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.
Title: Re: How does gravity exert its influence infinitely?
Post by: Kryptid on 28/05/2019 13:55:21
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.
Title: Re: How does gravity exert its influence infinitely?
Post by: Yahya A.Sharif on 28/05/2019 14:30:48
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.
Title: Re: How does gravity exert its influence infinitely?
Post by: Halc on 28/05/2019 14:44:27
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:
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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.
Title: Re: How does gravity exert its influence infinitely?
Post by: Halc on 28/05/2019 14:52:08
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.

Quote
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'.

Quote
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.

Quote
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.
Title: Re: How does gravity exert its influence infinitely?
Post by: Colin2B on 28/05/2019 15:02:43
@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.
Title: Re: How does gravity exert its influence infinitely?
Post by: alancalverd on 28/05/2019 15:11:16
Gravity has nothing to do with rotation. It is a function of mass only.
Title: Re: How does gravity exert its influence infinitely?
Post by: alancalverd on 28/05/2019 15:13:36
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?
Title: Re: How does gravity exert its influence infinitely?
Post by: alancalverd on 28/05/2019 15:14:24
@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!
Title: Re: How does gravity exert its influence infinitely?
Post by: Yahya A.Sharif on 28/05/2019 15:24:01
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.
Title: Re: How does gravity exert its influence infinitely?
Post by: Halc on 28/05/2019 15:52:04
@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.
Title: Re: How does gravity exert its influence infinitely?
Post by: Halc on 28/05/2019 15:55:39
so you are telling me that electromagnetic radiation has a gravitational field, and therefore F≠GMm/r2?
EM energy (any energy) has mass, thus GMm/r² still holds
Title: Re: How does gravity exert its influence infinitely?
Post by: Halc on 28/05/2019 16:02:08
It is a function of mass and energy, rotation will increase energy and increase gravity,
I agree that the rotation energy constitues mass, but it cannot appear out of nowhere.  Where did the rotation come from?  Some energy had to be taken from elsewhere to get it rotating, so the total gravity is unchanged.  You might as well have dropped a rock on it, which also adds to its mass, but removes one rock mass from the surrounding 'not planet' for a net gain of zero.
Without a net difference, there is no increment in gravity to feel after a delay.
Title: Re: How does gravity exert its influence infinitely?
Post by: Bored chemist on 28/05/2019 16:06:07
What do you mean by "available"?
It doesn't make sense in English to say "gravity is available everywhere".
Title: Re: How does gravity exert its influence infinitely?
Post by: Yahya A.Sharif on 28/05/2019 16:10:07
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"
Title: Re: How does gravity exert its influence infinitely?
Post by: Bored chemist on 28/05/2019 16:13:54
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".

Title: Re: How does gravity exert its influence infinitely?
Post by: Bored chemist on 28/05/2019 16:17:08
@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.
Title: Re: How does gravity exert its influence infinitely?
Post by: Bill S on 28/05/2019 16:40:45
As usual, I’m skimming threads, so may have missed a lot. However, to return to the OP, a few things come to mind.

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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.

Title: Re: How does gravity exert its influence infinitely?
Post by: Bill S on 28/05/2019 16:52:48
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.
Title: Re: How does gravity exert its influence infinitely?
Post by: Colin2B on 28/05/2019 18:11:54
@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.
Title: Re: How does gravity exert its influence infinitely?
Post by: alancalverd on 28/05/2019 19:07:16
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?
Title: Re: How does gravity exert its influence infinitely?
Post by: jeffreyH on 28/05/2019 19:50:06
Gravity has nothing to do with rotation. It is a function of mass only.

Now I've only been skimming this thread but Alan's post should be read and understood. It is a very important point and says a lot about translation in space over rotation. If a gravitational field actually rotated then the speed of information transfer becomes Galilean. Just think about that for a moment.
Title: Re: How does gravity exert its influence infinitely?
Post by: jeffreyH on 28/05/2019 20:04:47
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?

Now that is a very good point. I can't see how anyone could refute it. We see stars, therefore light does not beget gravity.
Title: Re: How does gravity exert its influence infinitely?
Post by: Kryptid on 28/05/2019 21:00:26
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?

Let's consider the case of a single star. How can the photons from that star focus each other into a beam if they are radiated in basically a spherically-symmetrical fashion? The pull in all directions would be about equal, so what direction do you propose the beam should point? Let's also not forget that the gravitational pull between something like rays of light would be incredibly weak, so distortions in the paths of electromagnetic rays would be overwhelmingly dominated by the gravity of planets and stars and even small asteroids.

A pair of X-ray photons with an energy of 100 keV (1.6022 x 10-14 J) would have a mass-energy equivalence of about 1.783 x 10-34 kilograms per photon. If the two start off 1 nanometer apart, they will experience a gravitational force between them of: F = (GMm)/r2, F = ((6.674×10−11)*(1.783 x 10-34)*(1.783 x 10-34))/(10-9)2, F = 2.1209 x 10-60 newtons.

Let's compare that with the gravitational force that each photon would experience from Alpha Centauri A if they started out 4.366 light-years away from it, F = (GMm)/r2, F = ((6.674×10−11)*(1.783 x 10-34)*(2.18735 x 1030))/(4.130236 x 1016)2, F = 1.5258 x 10-47 newtons. So even a star over 4 light-years away is pulling on each photon with a force more than 7 trillion times higher than they are pulling on each other.

The existence of gravitational lensing indicates that massive objects can pull on beams of light. So the beams of light must also be able to pull on those massive objects, otherwise we have a violation of Newton's third law.

How can the idea of a kugelblitz work if energy has no mass and therefore no gravity? https://en.wikipedia.org/wiki/Kugelblitz_(astrophysics)
Title: Re: How does gravity exert its influence infinitely?
Post by: Halc on 28/05/2019 23:38:29
I think perhaps this thread is full of misinformation, and we need to consider what we are saying.
I too think I am making gross generalizations by my statements.

I've been in the energy-has-mass camp, but I'd like to question some of the arguments for that side:

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.
My bold.  How exactly might one propose to get this energy away from Earth 'at no cost'?  Light doesn't work since it loses energy as it climbs out of a gravity well.  What sort of energy doesn't do that?  If we can't identify it, then this argument falls apart even if the conclusion was correct.

I can produce reactionless thrust if energy has no mass.   Consider two stationary weights.  I let them fall towards each other, but before they hit, I change one of them to energy, which I hold on to for a while.  The second mass now has momentum with no reaction mass.  That's reactionless thrust.

The arguments for the other side seem to have faults as well.
so you are telling me that electromagnetic radiation has a gravitational field, and therefore F≠GMm/r2?
It seems that all radiation has mass and is therefore subject to gravity.  EM radiation cannot escape a black hole, nor can gravitational radiation.  But the EM field and the gravitational field are still felt, implying that neither is something that travels, light speed or otherwise.  If gravity was something that traveled at light speed, gravity wouldn't be able to escape a black hole.

Kryptid's response to the 'focused light' from stars is spot on.  For all I know, a laser beam of light might be capable of holding itself together in that manner, but light from a star has equal 'density' in all directions, so the light has no imbalance to divert itself.

If a gravitational field actually rotated then the speed of information transfer becomes Galilean.
Nobody suggested a rotating field.  That's not the same as a field from a rotating object as compared to the field from the same object not rotating.  The former is presumably stronger since there is more mass/energy to the object.
Title: Re: How does gravity exert its influence infinitely?
Post by: Kryptid on 28/05/2019 23:43:00
How exactly might one propose to get this energy away from Earth 'at no cost'?  Light doesn't work since it loses energy as it climbs out of a gravity well.

My point was to illustrate that if energy does not have gravity, then turning the mass of the Earth into energy gets rid of the gravity well and thus you can move a weight away from the Earth at no energy cost. Since that violates conservation of energy, my conclusion was that turning the Earth's mass into energy mustn't actually remove the gravity well and therefore energy has gravity.
Title: Re: A question about gravity
Post by: Yahya A.Sharif on 29/05/2019 13:23:42
Gravity doesn't suddenly spring into existence out of nowhere. It has energy and energy is conserved.
The law of conservation of energy applies to our universe, but no-one knows if it applies before the big bang or not.
Mass popping from nowhere " before the big bang" will have gravity propagate with c and finite range, for mass to have infinite gravity range it should exist infinitely in time in the past so that its influence reaches infinite , but infinite time in the past is not logical.
Title: Re: How does gravity exert its influence infinitely?
Post by: Yahya A.Sharif on 29/05/2019 13:57:17
Energy causes gravity the same as mass , this is a well known fact according to Einstein's  theory of general relativity.
Title: Re: How does gravity exert its influence infinitely?
Post by: alancalverd on 29/05/2019 19:20:51
In principle, you should be able to convert the entire Earth's mass into energy.

That raises an interesting scenario, with cosmological significance. Suppose we spontaneously convert a spherical mass into photons. The resultant electromagnetic pulse will be a spherical shell, expanding at c.  From outside, the gravitational field will be unchanged, appearing to be generated at the original center of gravity, but inside the shell, the field will be zero.

We don't need to evaporate an entire planet to do this. Any mass-energy converter (like the sun) will be kicking off spherical EMP, with a decreasing local gravitational field but no change noticeable outside the "shell".

How does this affect our view of the mechanics of an expanding universe?

Title: Re: How does gravity exert its influence infinitely?
Post by: jeffreyH on 29/05/2019 20:07:40
When the sphere of photons reach objects in the gravitational field of the converted object gravity will stop having an effect. Anything orbiting the original mass will now move away with a possible momentum boost from interactions with the expanding photon sphere. Everything just expands away from the source.
Title: Re: How does gravity exert its influence infinitely?
Post by: alancalverd on 30/05/2019 01:46:06
Mass popping from nowhere " before the big bang" will have gravity propagate with c and finite range, for mass to have infinite gravity range it should exist infinitely in time in the past so that its influence reaches infinite , but infinite time in the past is not logical.

There's the source of misunderstanding! "Range" means the absolute limit of a quantity: the plane will fall out of the sky after 1500 miles, however long we wait,  because its fuel range is limited, but there is no theoretical limit to gravitational influence - if we wait long enough, with a sufficiently sensitive instrument, we will detect the creation of a distant mass. "Extent" means its actual position radius at any given time, which for gravity appears to be ct, and for our aeroplane, can be any value less than 1500 miles.

Colloquially, we sometimes use range to mean present radius where the context is unambiguous, e.g. "Target radar range is 10 miles, my gun range is 5 miles, so I can't hit the target, Captain."  "Wait."
Title: Re: How does gravity exert its influence infinitely?
Post by: Yahya A.Sharif on 31/05/2019 13:49:50
if we wait long enough, with a sufficiently sensitive instrument, we will detect the creation of a distant mass.
"if we wait enough " this is the problem , we can't wait infinitely so that gravity be everywhere to infinity.
However gravity behavior is exactly a definition of a finite range:
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 doesn't exert its influence infinitely then it has a finite range that is exactly what I claim
Title: Re: How does gravity exert its influence infinitely?
Post by: jeffreyH on 01/06/2019 11:02:40
Where is the boundary for gravity? If its range is finite then there must be a boundary. Is it the edge of the observable universe? Well, no, it can't be, since more of the universe will become observable over time.

The concept of infinity being a limit is not the same as infinity being a point in space. Infinity is not anywhere. Not physically. Gravity will never not have an effect, however small that effect might be. That is all it means.

This shouldn't be so hard to grasp.
Title: Re: How does gravity exert its influence infinitely?
Post by: Yahya A.Sharif on 01/06/2019 18:28:05
Where is the boundary for gravity? Is it the edge of the observable universe?
Newton has the idea of infinity in his work including infinite speed of objects, infinite gravity speed and gravity existing infinitely, all these concepts of infinity are wrong,  according to his idea if the sun disappeared suddenly the earth will lose its orbit at the same time of the sun's disappearance , gravity propagates with c means no infinity for its influence, if its influence reaches us with speed c then we have at a time three significant points , a point at which gravity exists , gravity propagates and cover such point, a point at which gravity doesn't exist this point is not covered by gravity propagation yet, and a point at the edge  in which gravity suddenly drops to zero this point is the BOUNDARY of gravity. Unfortunately we live within the gravity coverage of masses in the universe and the gravitational equation satisfies within this coverage , but the equation won't satisfy beyond its coverage.And for a rotating object experiment we would see how gravity has finite influence and range.
Title: Re: How does gravity exert its influence infinitely?
Post by: Yahya A.Sharif on 01/06/2019 18:41:53
Cut to the chase.
"How does gravity exert its influence infinitely?"
How could it not do so?
Because it has finite propagation speed.
Title: Re: How does gravity exert its influence infinitely?
Post by: Colin2B on 01/06/2019 19:37:57
Cut to the chase.
"How does gravity exert its influence infinitely?"
How could it not do so?
Because it has finite propagation speed.
Your answer is totally illogical as has been pointed out to you.
You are playing silly word games with infinite and finite, neither of which you fully understand.
End of
Title: Re: How does gravity exert its influence infinitely?
Post by: evan_au on 01/06/2019 23:07:20
Quote from: JeffreyH
Where is the boundary for gravity?
It would be anything outside the light cone of our masse.

According to the Big Bang theory, all the mass of the universe started off inside the light cone of the rest of the universe.

However, the addition of "Cosmic Inflation" to this theory means that there is some (now distant) mass that might be outside our light cone.

See: https://en.wikipedia.org/wiki/Inflation_(cosmology)