Gravity is a force .. not Energy

[swansont]

!

Moderator Note

post merged, since it's on the same topic

So energy in it self is not a force only a propriety .

That was not in question.

How about addressing the issue of photons, which are not matter, exerting a force? Rather than continuing to dodge?

[Mordred]

!

Moderator Note

post merged, since it's on the same topic

 

That was not in question.

 

How about addressing the issue of photons, which are not matter, exerting a force? Rather than continuing to dodge?

Feel free to use electrodynamics. Its a common circuit to use field interactions to cause signal delay aka interference.

 

Interference requires work. So does changing a frequency of any signal/excitation.

 

PS the photon is the gauge vector boson for the electromagnetic field.

 

Lets use an analogy to describe kinematic motion due to photons.

 

1) Every particle has energy...think about this and the definition of energy (the ability to perform work.)

2) just like the electromagnetic field proximity rather than direct collision can also cause force.

3) matter is a rather meaningless term in particle physics. (side note under ideal gas laws Einstein Crystal lattice is a good mathematical guideline) anyways matter has a requirement (taking up space) google Pauli exclusion principle. So only fermions count as matter.

 

4) matter exerts no pressure (force per unit volume) under cosmology the equation of state for matter is zero. This is due to matters lack of kinetic energy aka momentum.

 

5) photons despite not having rest mass do have inertial mass. As far as pressure influnce photons has a greater pressure influence than matter. Far greater kinetic energy.

 

Which is completely opposite of force requiring matter. Force only requires the amount of energy to perform the required work.

 

Bosons are the mediator particles for your force fields ie electromagnetic..being photon. We know force field interactions exert force under Newton

Edited May 7, 2017 by Mordred

[humility]

So... if you hit a spaceship with a laser or a beam of any kind of radiation. The spaceship woukd be slowly pushed by the laser until it hit the speed of light barrier? Why arent we doing this with our probes?

[swansont]

So... if you hit a spaceship with a laser or a beam of any kind of radiation. The spaceship woukd be slowly pushed by the laser until it hit the speed of light barrier? Why arent we doing this with our probes?

 

 

The impulse is very small. Great for manipulating atoms. Not so great when you have to divide the acceleration by Avogadro's number.

[pzkpfw]

Bit of a side point, really, but laser light also spreads more than many expect.

 

e.g. firing a laser at the Moon to determine distance, the laser beam is 6.5 km wide by the time it reaches the Moon. https://en.wikipedia.org/wiki/Lunar_Laser_Ranging_experiment

 

So at any distance, little of the laser light is going to hit the target probe.

 

(Also, there'd be few choices in direction.)

[Bender]

I'm wondering: is the question:

 

"Can a force be exerted between two massless particles, or is it always necessary for one of both sides to be matter?"

[Mordred]

Yes a force can be exerted between two massless particles.

[Handy andy]

So how did gravity work before there were atoms ? or fermionic matter? Not all the history of our universe was matter available.

 

Or better yet this lab experiment that uses lasers to generate a gravitational field?

 

http://iopscience.iop.org/article/10.1088/1367-2630/18/2/023009

 

Same article but published at arxiv for those that prefer arxiv.

 

https://www.google.ca/url?sa=t&source=web&rct=j&url=https://arxiv.org/pdf/1511.01023&ved=0ahUKEwi8-Lyz4dTTAhXpv1QKHYwOBbAQFggcMAA&usg=AFQjCNFV4HS0tqUmytAUIleAh6o9Sm_2vg&sig2=lnR3ot4f5VwB0k7zBMpXkg

 

 

Here is the more popularly known Tolman tests on lasers generating gravity.

 

https://redirect.viglink.com/?format=go&jsonp=vglnk_149385056757712&key=6afc78eea2339e9c047ab6748b0d37e7&libId=j29k06cn010009we000MAjvoizlu8&loc=https%3A%2F%2Fwww.physicsforums.com%2Fthreads%2Feffect-of-photon-gravity-on-another-photon-traveling-in-the-opposite-d.764878%2F&v=1&out=http%3A%2F%2Fauthors.library.caltech.edu%2F1544%2F1%2FTOLpr31a.pdf&ref=https%3A%2F%2Fwww.google.ca%2F&title=Effect%20of%20photon%20gravity%20on%20another%20photon%20traveling%20in%20the%20opposite%20d%20%7C%20Physics%20Forums%20-%20The%20Fusion%20of%20Science%20and%20Community&txt=http%3A%2F%2Fauthors.library.caltech.edu%2F1544%2F1%2FTOLpr31a.pdf

 

By the way that was done back in 1931...

 

Why we even have laser driven sails. How is that possible if only matter can generate force?

 

https://en.m.wikipedia.org/wiki/Laser_propulsion

 

I call that sufficient proof your wrong. Better study Roger

 

I am going to get kicked for asking this. But is it not the case that fermions, bosons, all forms of energy and matter, distort space, thus causing a gravitational effect?. Is it not the case according to general relativity that the contraction or expansion of space is the source of gravity?.

[Strange]

 

I am going to get kicked for asking this. But is it not the case that fermions, bosons, all forms of energy and matter, distort space, thus causing a gravitational effect?.

 

 

Yes.

 

 

 

Is it not the case according to general relativity that the contraction or expansion of space is the source of gravity?.

 

No.

[Handy andy]

 

 

Yes.

 

 

No.

 

A clever individual posted this about the Gullstrand-Painlevé coordinates. "These can be interpreted as space flowing towards a mass".

https://en.wikipedia.org/wiki/Gullstrand–Painlevé_coordinates

 

Would it be better for me to have reworded "according to general relativity the contraction or expansion of space is the source of gravity". to according to general relativity the flow of space towards a mass or source of energy is the source of gravity?

[Strange]

A clever individual posted this about the Gullstrand-Painlevé coordinates. "These can be interpreted as space flowing towards a mass".

https://en.wikipedia.org/wiki/Gullstrand–Painlevé_coordinates

 

Would it be better for me to have reworded "according to general relativity the contraction or expansion of space is the source of gravity". to according to general relativity the flow of space towards a mass or source of energy is the source of gravity?

 

 

The Gullstrand-Painlevé coordinates only apply to an unchanging, spherical, non-rotating mass in an otherwise empty universe. That might be a reasonable approximation to a few other cases. But it isn't clear that gravity can always be re-interpreted as the "flow of space". This seems to be a bit of a special case.

 

However, the description of gravity as the curvature of space and time is universal.

[Handy andy]

 

 

The Gullstrand-Painlevé coordinates only apply to an unchanging, spherical, non-rotating mass in an otherwise empty universe. That might be a reasonable approximation to a few other cases. But it isn't clear that gravity can always be re-interpreted as the "flow of space". This seems to be a bit of a special case.

 

However, the description of gravity as the curvature of space and time is universal.

 

Agreed.

 

Is it also true to say that any distortion of space causes gravity? and any source of energy or mass including photons distorts space?

and that gravity causes all forms of energy or mass to move towards the most stretched area of space?

 

Is it also true a photon can be represented as a wave, as can particles, and they all cause a disturbance or curvature of space around them?

 

Is the curvature of space just another way of saying gravity or distortion of space.?

 

Is gravity a measurable quantity or substance ?

Is space curvature a measurable quantity or substance ?

Is space a measurable quantity or substance ?

[zapatos]

So... if you hit a spaceship with a laser or a beam of any kind of radiation. The spaceship woukd be slowly pushed by the laser until it hit the speed of light barrier? Why arent we doing this with our probes?

 

It's in the works.

 

 

 

“Breakthrough Starshot,” the program Milner is backing, intends to squeeze all the key components of a robotic probe—cameras, sensors, maneuvering thrusters and communications equipment—into tiny gram-scale “nanocraft.” These would be small enough to boost to enormous speeds using other technology the program plans to help develop, including a ground-based kilometer-scale laser array capable of beaming 100-gigawatt laser pulses through the atmosphere for a few minutes at a time, and atoms-thin, meter-wide “light sails” to ride those beams to other stars. Each pinging photon of light would impart a slight momentum to the sail and its cargo; in the microgravity vacuum of space, the torrent of photons unleashed by a gigawatt-class laser would rapidly push a nanocraft to relativistic speeds.

 

 

https://www.scientificamerican.com/article/100-million-plan-will-send-probes-to-the-nearest-star1/

[Strange]

Is it also true to say that any distortion of space causes gravity?

 

 

I'm not sure. I would guess yes, but it may be possible to come up with some pattern of space-time curvature that does not cause gravity.

 

Actually, it is more accurate to say that space-time curvature is gravity, rather than causes gravity. (The latter implies that gravity is something separate from the space-time curvature.)

 

And note that is it space-time curvature, not just space.

 

 

and any source of energy or mass including photons distorts space?

 

Yes. And a few other things also contribute: momentum flow, stress, etc. You can find the gory details here:

 

 

 

and that gravity causes all forms of energy or mass to move towards the most stretched area of space?

 

I think that "most curved" may correspond to the presence of mass-energy (and therefore where things will move towards). But that probably needs a Mordred to answer.

 

 

 

Is it also true a photon can be represented as a wave, as can particles, and they all cause a disturbance or curvature of space around them?

 

All particles are also waves (or have wave-like properties). But this is not relevant for gravity. That just depends on their mass-energy.

 

 

 

Is the curvature of space just another way of saying gravity or distortion of space.?

 

Gravity is just one of the effects of the curvature of space-time (others are things like time dilation, red-shift, etc).

 

 

Is gravity a measurable quantity or substance ?

Is space curvature a measurable quantity or substance ?

 

They are both measurable quantities (because they are the same thing). But not substance.

 

 

 

Is space a measurable quantity or substance ?

 

It is measurable (pull out a ruler, for example) but not a substance.

[Mordred]

I think that "most curved" may correspond to the presence of mass-energy (and therefore where things will move towards). But that probably needs a Mordred to answer.

 

Close but we have to be careful here, curvature can be positive or negative. Gravity under the FLRW metric will correspond to negative curvature. However under GR its modelled as positive curvature.

 

The difference is in how the two metrics treat curvature. Under the FLRW metric positive curvature leads to expansion with negative curvature a contraction. Both involve the equations of state (details the pressure influence due to a particles kinetic energy.) The difference between GR (Einstein field equations ) and the FLRW metric amounts to just a change in vector direction (change in sign) between the two metrics.

 

Under GR which is a localized curvature under the FLRW greater positive curvature is your higher gravity.

 

The cosmological constant in both the FLRW and the Einstein field equations is the reverse curvature. (in GR it acts as an anti gravity) but this isn't the correct way to think of it. The correct way is to apply its pressure influence via its equation of state.

 

 

The cosmological constant has EoS of w=-1. Which means its kinetic energy causes on essence negative pressure or vacuum. So while the energy density is still positive its pressure influence is the reverse compared to matter and radiation (photons etc).

 

In this case higher energy density of the cosmological constant leads to greater expansion. While matter and radiation higher energy density leads to greater contraction.

 

So from the last paragraph we can see higher energy density does not necessarily mean greater gravity. (it does in all cases except the cosmological constant) which has a negative pressure influence.

 

Neither does greater spacetime curvature necessarily mean greater gravity. (normally true except with the pesky cosmological constant) which can literally the curvature sign (positive/negative)

Edited May 9, 2017 by Mordred

[Laughablestuff]

In quantum physics, if we can't prove gravitons exist. We can use ever more provable quantum field theory, to almost explain how and why our molecules react relatively to an extremely large mass.

[Handy andy]

Close but we have to be careful here, curvature can be positive or negative. Gravity under the FLRW metric will correspond to negative curvature. However under GR its modelled as positive curvature.

 

The difference is in how the two metrics treat curvature. Under the FLRW metric positive curvature leads to expansion with negative curvature a contraction. Both involve the equations of state (details the pressure influence due to a particles kinetic energy.) The difference between GR (Einstein field equations ) and the FLRW metric amounts to just a change in vector direction (change in sign) between the two metrics.

 

Under GR which is a localized curvature under the FLRW greater positive curvature is your higher gravity.

 

The cosmological constant in both the FLRW and the Einstein field equations is the reverse curvature. (in GR it acts as an anti gravity) but this isn't the correct way to think of it. The correct way is to apply its pressure influence via its equation of state.

 

 

The cosmological constant has EoS of w=-1. Which means its kinetic energy causes on essence negative pressure or vacuum. So while the energy density is still positive its pressure influence is the reverse compared to matter and radiation (photons etc).

 

In this case higher energy density of the cosmological constant leads to greater expansion. While matter and radiation higher energy density leads to greater contraction.

 

So from the last paragraph we can see higher energy density does not necessarily mean greater gravity. (it does in all cases except the cosmological constant) which has a negative pressure influence.

 

Neither does greater spacetime curvature necessarily mean greater gravity. (normally true except with the pesky cosmological constant) which can literally the curvature sign (positive/negative)

 

Just to be clear, are you saying it is not clear which is correct GR or FLRW. GR a localized curvature, FLRW greater curvature.

 

Which would you think is most likely correct, based on what is observed.

 

In quantum physics, if we can't prove gravitons exist. We can use ever more provable quantum field theory, to almost explain how and why our molecules react relatively to an extremely large mass.

 

Does this also cover how you respond to an extremely small packet of energy which causes a gravitational disturbance such as a photon of light.

[Mordred]

No both are equally accurate. The difference is simply an arbitrary choice in vector sign. One can readily use either metric with equal accuracy.

 

The arbitrary choice is simple, in the FLRW metric at the time the formulas were being developed. Hubble showed the universe was expanding. So the metric reflects this under the sign choice.

 

With gravity we know it causes contraction so the arbitrary choice was chosen to reflect contraction.

 

The only difference between the two is the sign choice. Ie which dynamic to make positive vectors are symmetric when you change directions to the opposite you only need to change the sign plus or minus.

 

The main detail of my last post is simply to point out.

 

One cannot arbitrarily think greater curvature or higher energy density means greater gravity. The cosmological constant is one case where this isn't true.

Edited May 9, 2017 by Mordred

[humility]

arent the terms matter and energy interchangeable?

[swansont]

arent the terms matter and energy interchangeable?

 

 

No, they are not. Matter is a classification. Mass and energy are properties. Photons, which are not matter and have no mass, possess energy

[humility]

Oh I thought the big deal with energy equals mass times the speed of light squared was that it meant mass and energy were the same thing. And I thought mass was another word for matter. Since Ive never seen an object as being described as having a lot of matter always a lot of mass.

Edited May 9, 2017 by humility

[Mordred]

Mass and energy are flip sides of the same coin.

 

Matter however is fermionic particles. Bosons are not matter.

[humility]

And fermionic particles is the name of those tiny little particles that always appear in pairs and if you split a pair they just stretch into two new pairs converting whatever energy you used to split them into more of themselves?

[swansont]

And fermionic particles is the name of those tiny little particles that always appear in pairs and if you split a pair they just stretch into two new pairs converting whatever energy you used to split them into more of themselves?

You're probably thinking of quarks, which are one kind of fermionic particle.

[humility]

oh ok. Tall Quarks, long Quarks.