# Naked Science Forum

## Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Bill S on 20/09/2018 20:24:21

Title: Does gravity have an infinite range?
Post by: Bill S on 20/09/2018 20:24:21
Experts seem to disagree.  For example;

https://www.quora.com/Does-gravity-have-infinite-range
David Wrixon EurIng, BSc(Hons), says: “No, it does not and cannot……. No it cannot have an infinite range.”

Jess H. Brewer, Professor Emeritus, Dept. of Physics & Astronomy says: “Yes, it has infinite range. No, its influence never reaches zero.”

http://wtamu.edu/~cbaird/sq/2015/06/09/does-the-influence-of-gravity-extend-out-forever/
Dr Chris Baird says: “In summary, the influence of gravity only extends to the edge of each galaxy group. Beyond that, spacetime no longer behaves like gravity.

So how does the “hitch-hiker” decide which expert to follow?  It would be easy to say, study their arguments and decide which one makes sense; but is the average “hitch-hiker” qualified to do this? Does he/she need expert help in making this decision?  If the answer is yes, then we have come full circle.

It seems fairly safe to assume that galaxy groups are held together by gravity; and that these groups move away from one another.  Could there be more than one explanation for this difference?

1.  The influence of gravity is (potentially) infinite, but, beyond the galaxy groups the influence of dark energy, or whatever drives the expansion of the Universe, is stronger than gravity.

2.  Gravity is quantised and eventually it reaches a point where it can diminish no further. Beyond that point, there is no gravity.

3.  Gravity is a force that is best defined in terms of spacetime curvature.  The further one is from the nearest matter, the less curvature there is, until a point is reached where there is no way of measuring the curvature.  Spacetime is effectively flat.

4.  The Universe is infinite.  It contains infinite energy.  Its natural state is one of expansion, driven by this infinite energy.  In this scenario, the presence of matter disrupts the “natural” state of the Universe by introducing gravitational attraction.
Title: Re: Does gravity have an infinite range?
Post by: Halc on 20/09/2018 20:47:34
I think some of the experts might be right, but are interpreting the question differently.
So the universe has no spatial limit, but does gravity of the Milky Way effect something beyond the Hubble Sphere?  It one way it cannot (Eurlng).  The galaxy doesn't specifically exist to a thing that distant, which yes, is an interpretive statement.  On the other hand, there is a general density of matter everywhere, impossible to escape at any distance (Brewer).  In relation to that very distant place, there is definitely something somewhere around here, and it contributes to the overall gravity well of even the most remote places.  There is nowhere where you have zero gravitational potential energy.  Potential energy is negative everywhere.

Anyway, certainly galaxy superclusters have an effect on each other, but that is for the most part balanced in all directions, so they don't accelerate towards each other. Spatial expansion gives the greater effect and the clusters are all separating.

As for your 3, yes, spacetime is pretty dang flat in the nowhere that is between clusters.  There is gravity, but again, it is balanced, so no net effect.
Title: Re: Does gravity have an infinite range?
Post by: Kryptid on 20/09/2018 22:57:13
Gravity obeys the inverse square law. It becomes arbitrarily weak with distances but its strength never goes to zero. At least as best as we can tell.
Title: Re: Does gravity have an infinite range?
Post by: guest45734 on 21/09/2018 08:58:33
1.  The influence of gravity is (potentially) infinite, but, beyond the galaxy groups the influence of dark energy, or whatever drives the expansion of the Universe, is stronger than gravity.

2.  Gravity is quantised and eventually it reaches a point where it can diminish no further. Beyond that point, there is no gravity.

I think 1 and 2 are the closest, the influence of gravity is eventually overcome by the influence of dark energy.

Gravity obeys the inverse square law. It becomes arbitrarily weak with distances but its strength never goes to zero. At least as best as we can tell.

That is main stream thought but not agreed by all. MOND was an early example that disagreed with this, the holographic universe and the entropic emergent gravity of Verlinde support the assumptions of MOND.

The inverse square law may only apply until the outer parts of a galaxy then in an inverse law applies kicks in. This negates the need for dark matter, which has not been observed.

Interestingly Verlindes ideas seem to be gathering support and are being tested by the mainstream scientific community. His ideas are based on quantum mechanics and string theory and include those things missing from EFE such as entanglement.

If particles can be entangled why cant space or at least virtual particles existing momentarily in space?
Title: Re: Does gravity have an infinite range?
Post by: evan_au on 21/09/2018 12:12:38
Some random thoughts: The Big Bang theory suggests a period of Cosmic Inflation, where for a moment, space expanded faster than the speed of light.

Gravity travels at the speed of light (in a vacuum). So for the moment before Cosmic Inflation, all matter was in the gravitational field of all other matter. This situation did not hold after Cosmic Inflation, nor does it hold for parts of the universe that are now beyond our Visible Universe.

So I suggest that:
- All of the universe once felt the gravitational pull of the rest of the universe, back at the Big Bang
- This was possible because the universe was not infinite, right after the Big Bang
- The effects of gravitational events that occur today (like colliding black holes) will propagate outwards at the speed of light, but will never reach the edge of the universe, as that is a receding boundary. So in this sense, the effects of gravity will have an infinite range in the infinite future (but also an infinitely small effect)...

Caveats:
- I really don't understand unification of the 4 forces in the early stages of the Big Bang.
- I really don't understand how quantization of gravity will affect this
Title: Re: Does gravity have an infinite range?
Post by: jeffreyH on 21/09/2018 13:37:07
If we look at a spacetime diagram of entangled photons moving away from each other, then signals between the two propagating at any point after divergence will never arrive. This is because the signal speed of this information is the same as the speed of the photon. There is no acceleration. Thrrefore, in a period of inflation,  the same situation arises for the propagation of gravity. So trying to incorporate entanglement into gravitation does not help.
Title: Re: Does gravity have an infinite range?
Post by: jeffreyH on 21/09/2018 13:48:55
@evan_au This may help with an understanding of the combination of forces.
http://hyperphysics.phy-astr.gsu.edu/hbase/Astro/unify.html
Title: Re: Does gravity have an infinite range?
Post by: jeffreyH on 21/09/2018 13:59:11
In the meantime a use FOR entanglement to determine the quantum nature of gravity has been proposed.
https://m.phys.org/news/2018-03-gravity-quantum-mechanics.html
Title: Re: Does gravity have an infinite range?
Post by: Bill S on 21/09/2018 16:13:04
Thanks for some thought-provoking responses.

Quote from: Halc
There is nowhere where you have zero gravitational potential energy.

GPE = mgh.  If h is the separation between two bodies; could h be infinite?  If so, what would be the GPE?

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…….. certainly galaxy superclusters have an effect on each other….

What is this effect, and how is it measured?

BTW. I agree that interpretation is an important factor, but if “yes” and “no” are both correct some clear interpretation is needed.
Title: Re: Does gravity have an infinite range?
Post by: guest45734 on 21/09/2018 17:43:12
Thrrefore, in a period of inflation,  the same situation arises for the propagation of gravity. So trying to incorporate entanglement into gravitation does not help.
I would disagree with this statement, or at least like to discuss it, but dont think it comes under the scope of this thread. Basically particles virtual or otherwise come into existence in pairs and ar elikely entangled at their creation.

Caveats:
- I really don't understand unification of the 4 forces in the early stages of the Big Bang.
- I really don't understand how quantization of gravity will affect this

These are interesting caveats, gravity might not be one of the fundamental forces and this may be why it has eluded unification to present. How does a graviton get out of a blackhole if it has too little energy to detect it ?? .

GPE = mgh.  If h is the separation between two bodies; could h be infinite?  If so, what would be the GPE?

At infinite distance dark energy overcomes gravity and pushes planets apart. Any GPE would be -ve,  assuming that both dark energy and gravity are manifestations of the same thing, entanglement of space time :)

In summary, Verlinde’s emergent gravity has withstood the first-line bullshit test. Yes, it’s compatible with general relativity. The comment was made by a notable mainstream physicist not by me or Verlinde.
Title: Re: Does gravity have an infinite range?
Post by: jeffreyH on 21/09/2018 18:40:56
Thanks for some thought-provoking responses.

Quote from: Halc
There is nowhere where you have zero gravitational potential energy.

GPE = mgh.  If h is the separation between two bodies; could h be infinite?  If so, what would be the GPE?

How can objects be separated by an infinite distance if infinity is not a number? If they can't then the gravitational field can approach infinity but never actually reach it. This means that the potential of the gravitational field never increases to a zero value. However it can get immeasurably close to zero. This happens very locally with an inverse square force. So almost everywhere in the universe is unaffected by the field of an object. Since there are limits on the sizes of object, they will naturally collapse above a certain size, this applies to all objects that we have knowledge of. This includes stars, planets and black holes.

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…….. certainly galaxy superclusters have an effect on each other….

What is this effect, and how is it measured?

BTW. I agree that interpretation is an important factor, but if “yes” and “no” are both correct some clear interpretation is needed.

Title: Re: Does gravity have an infinite range?
Post by: Bill S on 21/09/2018 20:17:44
Quote from: Kryptid
Gravity obeys the inverse square law. It becomes arbitrarily weak with distances but its strength never goes to zero. At least as best as we can tell.

If gravity is quantized, would you not run into a problem similar to that of trying to explain black body radiation classically?
Title: Re: Does gravity have an infinite range?
Post by: Bill S on 21/09/2018 20:30:25
Quote from: Evan
Gravity travels at the speed of light (in a vacuum). So for the moment before Cosmic Inflation, all matter was in the gravitational field of all other matter. This situation did not hold after Cosmic Inflation, nor does it hold for parts of the universe that are now beyond our Visible Universe.

This is a very relevant facet of the OP. I would interpret it as saying that there is no place in the Universe in which there is zero gravity, but not all parts of the Universe can feel the gravitational attraction of every other part.  Would that be a reasonable interpretation?

If so, it would contradict Chris Baird’s “…the influence of gravity only extends to the edge of each galaxy group. Beyond that, spacetime no longer behaves like gravity.”
Title: Re: Does gravity have an infinite range?
Post by: Bill S on 21/09/2018 20:35:09
How does a graviton get out of a blackhole if it has too little energy to detect it ?? .

It doesn’t!
Title: Re: Does gravity have an infinite range?
Post by: Bill S on 21/09/2018 20:50:56
Quote from: Jeffrey
How can objects be separated by an infinite distance if infinity is not a number?

I confess!  I included that just to see if someone would give that response.

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If they can't then the gravitational field can approach infinity but never actually reach it.

Not only can it can never reach it; it can also never approach it; but I know what you mean. :)

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This means that the potential of the gravitational field never increases to a zero value.

I assume you also disagree with Chris Baird.

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However it can get immeasurably close to zero.

Does this apply if gravity is quantized?
Title: Re: Does gravity have an infinite range?
Post by: jeffreyH on 21/09/2018 21:36:32
Quote from: Jeffrey
How can objects be separated by an infinite distance if infinity is not a number?

I confess!  I included that just to see if someone would give that response.

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If they can't then the gravitational field can approach infinity but never actually reach it.

Not only can it can never reach it; it can also never approach it; but I know what you mean. :)

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This means that the potential of the gravitational field never increases to a zero value.

I assume you also disagree with Chris Baird.

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However it can get immeasurably close to zero.

Does this apply if gravity is quantized?

The quanta of the field are distinct from the field itself. It is the energy of the field that I mean as opposed to the energy of the quanta. As far as Chris Baird is concerned I haven't followed any link to his opinions. So I can't comment on that. However, the gravitational field does not exist in isolation and other fields/forces must be taken into consideration. These may in some cases not only cancel the effects of gravity but also cause a repulsive force.
Title: Re: Does gravity have an infinite range?
Post by: Kryptid on 21/09/2018 22:11:24
If gravity is quantized, would you not run into a problem similar to that of trying to explain black body radiation classically?

I don't see why you would.
Title: Re: Does gravity have an infinite range?
Post by: Bill S on 22/09/2018 15:49:04
Quote from: Jeffrey
The quanta of the field are distinct from the field itself. It is the energy of the field that I mean as opposed to the energy of the quanta.

Confused!  If the field is quantized, isn’t it composed of quanta?  How do you make a distinction?

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As far as Chris Baird is concerned I haven't followed any link to his opinions. So I can't comment on
that.
I was referring only to the quote:”… the influence of gravity only extends to the edge of each galaxy group. Beyond that, spacetime no longer behaves like gravity.”

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However, the gravitational field does not exist in isolation and other fields/forces must be taken into consideration. These may in some cases not only cancel the effects of gravity but also cause a repulsive force.

That seems to accord with “1. The influence of gravity is (potentially) infinite, but, beyond the galaxy groups the influence of dark energy, or whatever drives the expansion of the Universe, is stronger than gravity”, from the OP.
Title: Re: Does gravity have an infinite range?
Post by: Bill S on 22/09/2018 15:50:58
Quote from: Kryptid
I don't see why you would.

I think it has something to do with "going to infinity" - or not. :)
Title: Re: Does gravity have an infinite range?
Post by: guest45734 on 22/09/2018 18:19:02
How does a graviton get out of a blackhole if it has too little energy to detect it ?? .

It doesn’t!

The definition of the graviton differs between theorys. The standard model states it is a 2 spin boson, others state it is a virtual particle, but as a virtual particle it exists as part of the quantum foam of space time. Quantum foam cant really be quantized
Title: Re: Does gravity have an infinite range?
Post by: geordief on 22/09/2018 18:48:55
was referring only to the quote:”… the influence of gravity only extends to the edge of each galaxy group. Beyond that, spacetime no longer behaves like gravity.”
Could there be a different type of spacetime curvature to model those regions?
Title: Re: Does gravity have an infinite range?
Post by: guest45734 on 22/09/2018 20:56:32
Quote from: Bill S on Today at 15:49:04
was referring only to the quote:”… the influence of gravity only extends to the edge of each galaxy group. Beyond that, spacetime no longer behaves like gravity.”
Could there be a different type of spacetime curvature to model those regions?

I am a simple fella, and to make things simple to visualize from all theorems.

1) Remove the mass from space time and observe it expanding and time ticking along quite happily.
2) Add a sun and space time slows its expansion rate. This causes the appearance of space time curvature and time to slow in the vicinity of gravity due to the added mass.
3) Start the sun spinning and you will observe frame dragging as the gravitational field spins with the sun or planet.
4) Create a spiral galaxy those solar systems nearer the centre are attracted with a inverse square law, those at the outer parts of the spiral are attracted with a inverse law (unless of course additional unobserved mass exists like dark matter or teapots)
5) As you move away from the spiral galaxy the effect of gravitational attraction disappears. A balance is achieved between repulsion due to dark energy and attraction due to gravity.
6) Moving even further away from the spiral galaxy gravitational repulsion is experienced due to the expansion of space and dark matter gravity has less and less effect the further you move away.

Noting all along that any individual galaxies are accelerating away from each other due to dark energy, objects in those galaxies are in free fall with respect to other galaxies and feel no acceleration due to dark energy/cosmological constant.

Dark energy is likely due to entangled virtual particles filling all of the vacuum of space, this entanglement breaks down near matter.

Quantum entanglement works at the quantum level on particles why not virtual particles, the graviton could be a pair of entangled virtual particles.

Space time would smoothly expand in all directions if it was not for mass absorbing it, causing space time curvature.

Spooky action at a distance entanglement caused the development of the EPR wormhole theory, which is arguably for some equal to the ER wormhole theory written a month after the EPR theory.

Amusing after thought: in the northern hemisphere all hurricanes rotate anti clockwise in the southern hemisphere they rotate clockwise. In the part of the solar system we see all but a very few galaxies at the outer edge of the solar system rotate clockwise. Could we be on the southern hemisphere of a black hole.
Title: Re: Does gravity have an infinite range?
Post by: Bill S on 23/09/2018 12:29:07
The definition of the graviton differs between theorys. The standard model states it is a 2 spin boson, others state it is a virtual particle, but as a virtual particle it exists as part of the quantum foam of space time. Quantum foam cant really be quantized

However true all that may be, it doesn’t mean that gravity escapes from a BH.

If a star collapses into a black hole, the gravitational field remains outside the black hole, nothing has to escape to maintain the spacetime curvature.
Title: Re: Does gravity have an infinite range?
Post by: Bill S on 23/09/2018 12:40:06
Quote from: Geordief
Could there be a different type of spacetime curvature to model those regions?

Possibly; but if spacetime curvature is just a model describing the gravitational force, this would suggest a “different type” of gravity in those regions. Any thoughts?
Title: Re: Does gravity have an infinite range?
Post by: Bill S on 23/09/2018 13:21:45
1) Remove the mass from space time and observe it expanding and time ticking along quite happily.

How would you know space was expanding and time was doing anything?

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4) Create a spiral galaxy those solar systems nearer the centre are attracted with a inverse square law, those at the outer parts of the spiral are attracted with a inverse law (unless of course additional unobserved mass exists like dark matter or teapots)

Surely, the inverse square law would apply throughout, but its effect would be modified by the addition of “teapots” etc.

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5) As you move away from the spiral galaxy the effect of gravitational attraction disappears. A balance is achieved between repulsion due to dark energy and attraction due to gravity.

I think you would have to move out of the galaxy group for this to be the case.

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6) Moving even further away from the spiral galaxy gravitational repulsion is experienced due to the expansion of space and dark matter gravity has less and less effect the further you move away.

Not clear what you mean by “gravitational repulsion”, or what role dark matter plays in lessening the effects of gravity.
Title: Re: Does gravity have an infinite range?
Post by: geordief on 23/09/2018 15:30:23
Quote from: Geordief
Could there be a different type of spacetime curvature to model those regions?

Possibly; but if spacetime curvature is just a model describing the gravitational force, this would suggest a “different type” of gravity in those regions. Any thoughts?

Well (obviously) I wonder what is causing the galaxies to recede from each other ,and whether this recession (it seems not) is affected by the mass of the individual galaxies.

If it is a uniform recession ,then I guess that  spacetime curvature is a bad model for that as (so I hear) the global spacetime  curvature is the sum of all the local curvatures caused by the distribution of mass and energy.

I like(so what,of course) this idea of quantized gravity and wonder whether this recession is just the playing out of the absolute lack of gravity at these great distances(could that be the definition of a galaxy?)

Very interesting thread by the way,very new to me.
Title: Re: Does gravity have an infinite range?
Post by: Bill S on 23/09/2018 16:08:47
Quote from: Geordief
Well (obviously) I wonder what is causing the galaxies to recede from each other, and whether this recession (it seems not) is affected by the mass of the individual galaxies.

As yet, no one has tackled “explanation” 4, from the OP.  I live in hopes.

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….the global spacetime  curvature is the sum of all the local curvatures caused by the distribution of mass and energy.

If local spacetime curvature is a model for gravity, wouldn’t this imply that global spacetime  curvature tells us something about the possible gravitational state of the Universe, but has no real meaning beyond that?

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I like(so what, of course) this idea of quantized gravity and wonder whether this recession is just the playing out of the absolute lack of gravity at these great distances(could that be the definition of a galaxy?)

Hopefully, more of our resident experts will weigh in on the question of quantized gravity.  Would this limit the range of gravity, because its effect could not “go to infinity”?

In response to your "so what" clause; I would say that liking something is a good starting point for studying it, as long as you avoid "cherry-picking".
Title: Re: Does gravity have an infinite range?
Post by: Halc on 23/09/2018 16:18:27
Thanks for some thought-provoking responses.
Sorry for the reply delay, but I'm still figuring out this site, and there seem to be no notifications about replies to my posts if I turn off the emails.

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Quote from: Halc
There is nowhere where you have zero gravitational potential energy.

GPE = mgh.  If h is the separation between two bodies; could h be infinite?  If so, what would be the GPE?
I wasn't talking about a specific body.  I'm talking about the general GPE that is mostly due to the most nearby objects.  The most remote places anywhere are still only a billion or two light years from several of the closest superclusters.  You cannot get away from them any further and raise your GPE all the way to zero.

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…….. certainly galaxy superclusters have an effect on each other….

What is this effect, and how is it measured?
Gravity attracts, what else?  Maybe the effect offers resistance to the rate at which the expansion of space would otherwise proceed.  The effect doesn't really change the trajectory of the superclusters significantly since they pretty much cancel each other out, being reasonably well distributed in all directions.

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BTW. I agree that interpretation is an important factor, but if “yes” and “no” are both correct some clear interpretation is needed.
Well, I said 'no, gravity is limited' in relation to the event horizon.  Gravity waves propagate at light speed, and so gravitons cannot ever reach an object beyond the event horizon and effect it there.
Gravity itself does not propagate, and so I cannot claim that mass here has zero effect on stuff beyond the event horizon.  I can claim it has no net effect since any pull from our direction is balanced by equal pull from the opposite direction.
Title: Re: Does gravity have an infinite range?
Post by: geordief on 24/09/2018 02:09:46

As yet, no one has tackled “explanation” 4, from the OP.  I live in hopes.

I just tried to address that ,but nothing intelligible came out.

Back to the ouija board I guess ;)
Title: Re: Does gravity have an infinite range?
Post by: guest45734 on 26/09/2018 10:06:19
4.  The Universe is infinite.  It contains infinite energy.  Its natural state is one of expansion, driven by this infinite energy.  In this scenario, the presence of matter disrupts the “natural” state of the Universe by introducing gravitational attraction.

Infinite size is unreachable, undefined, or uncalculable. Both Guth and Linde suggest an inflationary universe, Evidence appears to support Lindes combined with Guths earlier ideas. The edge of our universe is already unreachable to us and is expanding away from us. During the inflationary stage of the universe it is supposed to have expanded faster than light. The observed universe today is expanding at 3 x faster than light.

To an observer inside our universe today or inside the big bang inflationary stage of the universe, both would have observable horizons moving away from them at faster than light, so light emitted on the horizons would never reach them. Could the event horizon in both instances be regarded as infinity ie unreachable for the observer .

Edit Note I have not mentioned entanglement, EPR bridges or anything that might be involved when particles are created.:)

Edit : A short Linde utube on inflationary theory
Title: Re: Does gravity have an infinite range?
Post by: Bill S on 26/09/2018 20:29:13
Infinite size is unreachable,
Agreed.

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…Could the event horizon in both instances be regarded as infinity ie unreachable for the observer.

No.  This arises from – and leads to further – confusion.  Infinite and unreachable are not synonymous.

There are similarities between this and the speed of light.  E.g.

Nothing can be accelerated from subluminal to superluminal speed.
Nothing can progress from finite to infinite.

Title: Re: Does gravity have an infinite range?
Post by: evan_au on 26/09/2018 22:42:40
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the question of quantized gravity.  Would this limit the range of gravity, because its effect could not “go to infinity”?
The photon is quantized in energy at time of emission.
And it will propagate "to infinity" with this energy in the frame of reference in which it was emitted.
So there is nothing fundamental that would prevent a quantized graviton from propagating to infinity.

Because the universe is expanding, distant observers will detect the photon with less energy than it was emitted.
But we know of no lower limit to the energy of a photon, so there is no fundamental reason why this photon should not be detected by any object within its light cone.
The same rationale applies to the hypothetical graviton - its (already infinitesimal) energy will be even lower when detected by a distant observer, but that won't block their propagation.

Title: Re: Does gravity have an infinite range?
Post by: geordief on 27/09/2018 00:54:40
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the question of quantized gravity.  Would this limit the range of gravity, because its effect could not “go to infinity”?
The photon is quantized in energy at time of emission.
And it will propagate "to infinity" with this energy in the frame of reference in which it was emitted.
So there is nothing fundamental that would prevent a quantized graviton from propagating to infinity.

Because the universe is expanding, distant observers will detect the photon with less energy than it was emitted.
But we know of no lower limit to the energy of a photon, so there is no fundamental reason why this photon should not be detected by any object within its light cone.
The same rationale applies to the hypothetical graviton - its (already infinitesimal) energy will be even lower when detected by a distant observer, but that won't block their propagation.

But will it only propagate as far as there is something to detect it?

What happened/is happening to the first photon that emerged after the Big Bang? Is it condemned to never be detected (=have an interaction) ?

Or are we just talking about an expanding wave that retains its energy  "for ever" ?
Title: Re: Does gravity have an infinite range?
Post by: guest45734 on 27/09/2018 09:57:51
What happened/is happening to the first photon that emerged after the Big Bang? Is it condemned to never be detected (=have an interaction) ?

Playing with Lindes multiverse ideas. If space is expanding faster than light at the big bang, and is curved in some way, a photon could be moving into new space all the time, inside a curved universe.
Title: Re: Does gravity have an infinite range?
Post by: evan_au on 27/09/2018 10:56:18
Quote from: geordief
the first photon... Or are we just talking about an expanding wave that retains its energy  "for ever" ?
You can view light as particles (photons) or expanding waves - until you detect a photon.
At this point you must treat it as a particle at a certain particle, which has a certain energy, rather than a very low intensity wave.
Title: Re: Does gravity have an infinite range?
Post by: geordief on 27/09/2018 11:15:33
What happened/is happening to the first photon that emerged after the Big Bang? Is it condemned to never be detected (=have an interaction) ?

Playing with Lindes multiverse ideas. If space is expanding faster than light at the big bang, and is curved in some way, a photon could be moving into new space all the time, inside a curved universe.
I feel more comfortable thinking that space only expands as a function of objects within it. I am uncomfortable  of objects moving into "virgin" expanded space.

The object is always at the "leading edge" of the expanding space in my mind (and "pulling" the new space -but I realize this is probably a hopelessly inadequate attempt at a scenario)

Of course ,if you are introducing more then one universe ,that immediately seems more reasonable.
Title: Re: Does gravity have an infinite range?
Post by: Bill S on 27/09/2018 19:18:40
Quote from: Evan_au
The photon is quantized in energy at time of emission.
And it will propagate "to infinity" with this energy in the frame of reference in which it was emitted.
So there is nothing fundamental that would prevent a quantized graviton from propagating to infinity.

Would this mean that, if gravity is quantized, in any given space, a point would be reached where there was only one graviton in that space, so gravity could decrease no further?
Title: Re: Does gravity have an infinite range?
Post by: jeffreyH on 27/09/2018 19:34:21
Item 4 of OP. If there is infinite energy then the balance of positive versus negative energy is important. Does the total positive pressure balance the total negative pressure?
Title: Re: Does gravity have an infinite range?
Post by: geordief on 28/09/2018 01:09:39
Would this mean that, if gravity is quantized, in any given space, a point would be reached where there was only one graviton in that space, so gravity could decrease no further?
From evan_au's  last post I deduced that the graviton only inhabited that space to the extent that it was detected (ie had a gravitational effect on something).

With space being ever sparser it would only exist as a gravitational wave and maybe its quantum nature would not be apparent or relevant....if that makes sense.
Title: Re: Does gravity have an infinite range?
Post by: guest45734 on 28/09/2018 09:06:05
Nothing can be accelerated from subluminal to superluminal speed.

This is only a small point but relevant to other points on this thread. The current standard physics model of the big bang indicates the universe expanded faster than light in the inflationary stage, also the outer part of the visible universe is currently moving away from us at 3 x c. This does not mean it is being accelerated at these speeds but the actual space between objects is increasing. This is I understand driven by dark energy.

I feel more comfortable thinking that space only expands as a function of objects within it. I am uncomfortable  of objects moving into "virgin" expanded space.

The object is always at the "leading edge" of the expanding space in my mind (and "pulling" the new space -but I realize this is probably a hopelessly inadequate attempt at a scenario)

This I think is incorrect, space time expands as a result of dark energy not matter and gravity.

Would this mean that, if gravity is quantized, in any given space, a point would be reached where there was only one graviton in that space, so gravity could decrease no further?

This is an incredibly interesting observation. The graviton is generally considered to be a virtual particle although its description seems to change depending on which pop science article you read, or scientist you speak to.
There is no such thing as a vacuum in space, everywhere in space time is filled with virtual particles existing only momentarily. Dark energy is also thought to be caused by virtual particles/quantum fluctuations. If there are no quantum fluctuations space time does not exist, if they freeze frame time stops ticking.
Simplistically viewing the graviton as a virtual particles whose density (note did not mention entanglement or entropy)is reduced via mass. At a black hole event horizon, the graviton density may be reduced to near zero, as it may have been before the inflationary stage of a big bang, when matter and gravity came into existence.

Philosophical question could a dimension with no virtual particles be regarded as a gravity well or -ve energy which could give rise to the production of +ve energy to cancel it, maintaining a zero energy universe

Hey Ho not a clue, I must read more Lindes theories on an inflationary universe when I get back home.

Does a universe existing in a space full of multiverses have infinite space time dimensions ?
Title: Re: Does gravity have an infinite range?
Post by: Bill S on 28/09/2018 13:14:19
Quote from: Jeffrey
Item 4 of OP. If there is infinite energy then the balance of positive versus negative energy is important. Does the total positive pressure balance the total negative pressure?

Item 4 was, to a great extent, a fishing trip by the resident "infinity crackpot". :)

Before attempting to answer your question, we would have to consider whether an infinite universe could contain a finite amount of energy.
Title: Re: Does gravity have an infinite range?
Post by: Bill S on 28/09/2018 13:21:18
Quote from: Geordief[/quote
From evan_au's  last post I deduced that the graviton only inhabited that space to the extent that it was detected (ie had a gravitational effect on something).

Is that tantamount to saying that a particle is just an excitation of its field, and that it exists as a particle only as a result of field/field interaction?
Title: Re: Does gravity have an infinite range?
Post by: Bill S on 28/09/2018 13:46:20
This I think is incorrect, space time expands as a result of dark energy not matter and gravity.

Obviously, it’s OK to think this, but as we have seen elsewhere the whole question of dark matter is being given serious reconsideration.

Quote
The graviton is generally considered to be a virtual particle although its description seems to change depending on which pop science article you read, or scientist you speak to.

A characteristic it shares with many other concepts in physics/cosmology – sadly.

Quote
….whose density…..is reduced via mass

Not sure what you mean.
Title: Re: Does gravity have an infinite range?
Post by: guest45734 on 28/09/2018 14:49:44
Not sure what you mean.
The clue was in brackets, in the same sentence, of the post.
Title: Re: Does gravity have an infinite range?
Post by: geordief on 28/09/2018 14:58:52
Quote from: Geordief[/quote
From evan_au's  last post I deduced that the graviton only inhabited that space to the extent that it was detected (ie had a gravitational effect on something).

Is that tantamount to saying that a particle is just an excitation of its field, and that it exists as a particle only as a result of field/field interaction?
That is my "understanding". So the "first photon" would occur where the first expanding wave  interacted with something* -and the same would apply to the first gravitational wave/graviton.

I am ad libbing of course  so don't expect to  be required to seriously back up my interpretation as it is doubtless flawed in all sorts of directions,but as I said earlier it seems an interesting subject(which I have no grounding in)

*what?