I heard that the speed of gravity was the same as light

[skwinty (Steve)]

Originally Posted by Bassnut

43%?, that implies black hole remnants last for ever. I read somewhere black holes evaperate altogether in something like 10*250 years?. 43% over what, a period of time?.

And, if information is not preserved, doesnt that stuff causality. I thought if time was reversable, you could recreate any state in the past?.

Hi Fred
Here is an article from Scientific American about this issue.

[Bassnut (Fred)]

Excellent, thank you Steve

[xelasnave]

What an interesting thread...gravity interests me and I have specific views on the accumulation of truths we hold up as the final word on the subject..but for my investigations I say no one really knows zip and as such I add my thoughts to this thread even though it is now old and expired.
Newton ..the man who discovered gravity notwithstanding his apparent scientific approach to the subject and the extraction of many usable and relevant formulea when pressed for an explanation as to the force of gravity presented his view...the force of gravity is due to God ...most scientific observation prompted by a recognition that the Church was very jealous about taking power away from God....
Is there anyone reading this who is content to accept Newtons idea that gravity is due to the force of God???
So all is well...at the time Newton was working on gravity he was exposed to the "push" concept of gravity..an associate shared this view and Newton was aware..rather than endorse a push force or a force of attraction (horrors) Newton still left grqavity to God... interestingly the Church hunted down the push gravity guy and finished him off..for the reason he lead a band of children ...this was the reason cited by the church for the hunt however I feel it was this chaps determination to attribute gravity to a force other than God that got the church after him....and so who is next on the gravity subject...Dr A of course...and do we get Dr A buying into the force aspect of gravity..no way..Dr A's genius was in the fact that he provided knowledge of gravity that in no way erroded God's power to provive it... So we now ask someone who understands general relativity about gravity and are told there is no force..it is as if the sums make the objects move..force who needs a force..the sums make it work..I feel that view misses a realtiy which should no have to be explained but to those who need explaination can not see that gravity needs a force..the sums are not enough to make gravity work...
Gravity I feel can be expalined as an external pushing force perhaps due to particle pressure... dark energy can only work as an external pushing force and I suspect that gravity is an extention of what we now call dark energy.

However my point is General Relativity certainly describes gravity as not needing a force however such an approach I feel fails to appreciate sums alone do not govern the Universe they can merely interprete matters that are in play...
alex

[TrevorW]

The speed of light is constant in a vacumn light consists of photons, electromagnetic particles that can either act as as a particle or as a wave depending on the observer. Gravity is a force or wave, the effects of gravity can change depending on the mass of an object and diminish with distance. Gravity is a product of the distortion of time and space caused by the mass of an object.

[xelasnave]

Thanks Trevor for that....you said.......

"Gravity is a product of the distortion of time and space caused by the mass of an object."

My statement is that there must be more at work than the sums of general relativity which raises the question in my mind...

"how does mass distort time and space?..... there must be a machinery in real terms.. an interaction of particles perhaps?..a communication of "waves" between masses...it is an interesting question ..the very one avoided by Newton and Dr A.

Or how does the force of gravity (remembering GR does not speak of a force) get from one place to another...

Neither Newton or DrA speaks of how the force may work ...

Gravity must be more than the force of God one could expect.

alex

[skwinty (Steve)]

Gravity is classically characterised by space time geometry as a gravitational field.

General Relativity holds true when the distances involved are greater than the Planck-Wheeler Length. (This is the shortest distance that can be accurately measured).

When distances are shorter than the Planck-Wheeler Length then General Relativity breaks down, hence the search for a quantum gravity theory.

Now, the holy grail of physics is the unification of Gravity, Weak, Strong Nuclear Force and the Electromagnetic Force.

Now, Gravitational Waves or perturbations in the gravitational field is the domain of the graviton. This hypothetical particle has zero rest mass ( I didnt know they non catholic )

Gravitational waves can be detected by 4 methods.

1. Extremely low frequency gravitational waves left their imprint on the microwave cosmic background.

2. Very low frequency gravitational waves influence radio waves propogated by pulsars.

3. Low frequency gravitational waves influence on radio transmissions between earth and interplanetary space craft. This will be replaced in 2012 by LISA or Laser Intereferometer Space Antenna.

4 High frequency gravitational waves measured by earth based detectors ie LIGO or Laser Interferometer Gravity Obsevatories.

Seems as though the Michelson-Morley apparatus has grown up and forgotten about the ether

[edwardsdj (Doug)]

Originally Posted by xelasnave

"how does mass distort time and space?..... there must be a machinery in real terms.. an interaction of particles perhaps?..a communication of "waves" between masses...it is an interesting question ..the very one avoided by Newton and Dr A.

Or how does the force of gravity (remembering GR does not speak of a force) get from one place to another...

Neither Newton or DrA speaks of how the force may work ...

Hi Alex,

The first part you raise is the issue. In metric theories of gravity (the class of theories to which the General Theory of Relativity belongs) matter/energy is put in by hand. GR is not a theory of matter. This is what quantum theory is all about.

It is important to understand that in GR space and time do not have an independant existance. It is the "spacetime" that is warped by the presence of matter/energy as per the Einstein equation.

It is the warping of the spacetime that causes bodies (like the Earth) to appear to follow a curved path. All bodies are actually following a straight line in a curved spacetime geometry.

In this way Eisteins theory explains the action of gravity at a distance (unlike Newton's theory). What GR doesn't explain is the mechanism by which matter causes the spacetime to curve. This is what quantum gravity is all about.

The first fairly comprehensive theory of matter that we humans have developed (quantum theory) doesn't include gravitational effects. It is played out in the flat spacetime of special relativity.

Have fun,
Doug

[xelasnave]

Thanks for the interest fellow travellers

Steve mentioned......"Now, the holy grail of physics is the unification of Gravity, Weak, Strong Nuclear Force and the Electromagnetic Force."

Steve I think about this all the time... and if you take this in confidence and dont spread it around I can tell you that the push gravity approach that I have subscribed to certainly has the opportunity to do this....
At one stage Hawking said he received at least one paper a day claiming the grail was contained therein.


Doug said..........
It is important to understand that in GR space and time do not have an independant existance. It is the "spacetime" that is warped by the presence of matter/energy as per the Einstein equation.

Yes I understand this...... a pythagoras therom with a "fourth" ..side or arm... time....which time "changes" as space bends from an influence of local mass...

What I do not grasp is why mass needs to seek a "straight" path which is in point a line of the least resistence (of space) conecting to the most local "bent" space.... or what is it that tells the Sun to follow its "straight" line to where ever it seems to be headed...

I see a space/time grid as geometry that seeks to describe "space" in a way we can measure and relate our presence within it (space)....why that grid dictates that a section of the grid describing space say near the Sun becomes "small" and as such masses in a part of the grid with bigger squares (less space curve) are bound to move..in a straight line..to the point where space is bent more...is the aspect I miss...what dictates this within the grid or the math??? I get to a point where I can see a grid much like a weather map showing highs and lows (of gravity or intensity of space curvature) but can see no rule that says the high must move to the lower pressure areas....

Dont worry about trying to field my concern I am reasonably happy with all that I can understand of the way current science approaches the matter..

Thanks for all the neat information....

alex

[xelasnave]

As to eather..however it is spelt?...
I find it strange that given the regular new findings of various particles..nuetrinos alone could fit the bill of eather...and of course they are not the only candidates...
I feel some science is guided by fashion and I detect the fashion was to get rid of the old Greek thinking... eather was tossed..but the atomists continued..which offers some authority that some of their thinking openned doors to a greater wider truth..
So fashion removes the eather/.. loyalist will point to the Morely experiment.. but how does this answer the nuetrino abundance and stll say ..there is no eather...
I know this is a contentious matter.. but I think its time for fashion to make a move to perhaps idenify space as containing stuff..lots of stuff... billions upon billions of particles..all of which I feel rasonably be grouped to be called "space" (a no longer "empty" medium) or indeed..eather..the group of the billions of particles we now recognise as being there in abundance.
I like the eather because I feel it will provide the particle pressure required by a push gravity approach...

Why do galaxies hold together...dark matter we currently believe... is dark matter or dark energy a candidate for the eather??? but it is clear that dark energy acts as an external pushing force as a galaxy can not be bound simply by internal forces of attraction.. the distances prevent sensible relays of gravity messages...they are limited to the speed of light and thereofre take over one hundred thousand years for actions to be noticed on the other side of the gallaxy....an external force will work an intrnal force will not...or so I believe...
Sorry for the unsolicited rambling
alex

[edwardsdj (Doug)]

Originally Posted by xelasnave

Yes I understand this...... a pythagoras therom with a "fourth" ..side or arm... time....which time "changes" as space bends from an influence of local mass...

What I do not grasp is why mass needs to seek a "straight" path which is in point a line of the least resistence (of space) conecting to the most local "bent" space.... or what is it that tells the Sun to follow its "straight" line to where ever it seems to be headed...

Hi Alex,

It is important to understand that in GR space and time do not have an independant existance. It is the "spacetime" that is warped by the presence of matter/energy as per the Einstein equation.

What one observer perceives at space, another in a different frame of reference may perceive as time. It is only be considering the spacetime (often written space-time but never space/time - they are not separate in any physically meaningful way) that the physical nature of the situation can be understood.

The notion of time being a "fourth" side or arm is Netwonian theory. I cannot stress enough that it is not the "space" that is warped by matter/energy in GR: it is the "spacetime".

In this way a body in an inertial reference frame (in free-fall like the Earth in orbit around the Sun) moves in a straight path through the spacetime which from the frame of reference of the Sun appears to be an ellipitical path though the space over time (to a good approximation anyway).

I seem to recall first reading something like the "push" concept of gravity in Richard Feynmann's little book "The Character of Physical Law" as effort to show the reader a possible physical explanation of Newtonian gravitation. As I recall, it was a concept he held up as a straw man in order to shoot it down. Unfortuantely I cannot find an online copy of this great little book

Take care,
Doug

[xelasnave]

Thank you Doug.
I have a morosophic attachement to the push concept..in part because when I first thought of the idea I was unaware that it was already a very old concept (1745 is the date attached to LeSage having the idea)... thinking it was my original idea I worked on it for a long time before I realised it was already out there... I focussed upon it because it was the only way I could make gravity work..assuming I was left to build that part of the Universe... but right or wrong trying to engage the subject of gravity has seen me reading all sorts of stuff I never would have bothered with... and with each question answered being replaced with more questions.

Many will not accept the push concept and our mate is not the only man to have argued against it..assuming reasonably that as you say he held it up to tear it down........and I respect the chap particulary for his surprising statement given his profession....

"love nature..hate mathematics.."

For a moment I felt he could be converted but I suspect the statement held deeper meaning ..perhaps that nature was indeed the embodiment of mathematics.

If gravity pushes the space craft that leave our solar system will get "stuck" they will appear to slow, finally stop and then appear to race away at approx 350 kms per second....
I dont think I cut across GR as I can not see that it says gravity pushes or pulls no could it if the underlying aspect of the theory is that there is no force attached to gravity.

So there is a prediction to maybe escalate the idea to a theory..

I reckon the Corona of the Sun is due to the out flow of the Sun's energy meeting the inflow of the particle pressure I associate with what makes up gravity...and I feel that is reasonable in principle as certainly that approach does not require systems that are not apparent to supply the vast energy to have the Corona so much hotter than the Sun's surface. I do not see the suggestions that hot gas is transfered "up there" as viable...and even those speculations say that only one 10,000th of the energy can be taken up that way...sorry drifting off a little.... but push fits so well.

I also feel push gets rid of the need for dark matter and push explains the motions of outter stars orbital speed... and to me I think a Universe where we can see most of the matter more desirable than one where we need unsceen matter to make up the greater percentage of all that is....

However at this point in time I feel my views have some way to go before they are generally accepted

I do say however it is the flow of particles that "bend" the space time grid... so I see no conflict ..I should be able to use most of the GR stuff to finally support my ideas

Have a great day I must get back to the Lab
alex

[sjastro]

Originally Posted by xelasnave

If gravity pushes the space craft that leave our solar system will get "stuck" they will appear to slow, finally stop and then appear to race away at approx 350 kms per second....
I dont think I cut across GR as I can not see that it says gravity pushes or pulls no could it if the underlying aspect of the theory is that there is no force attached to gravity.

So there is a prediction to maybe escalate the idea to a theory..

I reckon the Corona of the Sun is due to the out flow of the Sun's energy meeting the inflow of the particle pressure I associate with what makes up gravity...and I feel that is reasonable in principle as certainly that approach does not require systems that are not apparent to supply the vast energy to have the Corona so much hotter than the Sun's surface. I do not see the suggestions that hot gas is transfered "up there" as viable...and even those speculations say that only one 10,000th of the energy can be taken up that way...sorry drifting off a little.... but push fits so well.

I also feel push gets rid of the need for dark matter and push explains the motions of outter stars orbital speed... and to me I think a Universe where we can see most of the matter more desirable than one where we need unsceen matter to make up the greater percentage of all that is....

However at this point in time I feel my views have some way to go before they are generally accepted

I do say however it is the flow of particles that "bend" the space time grid... so I see no conflict ..I should be able to use most of the GR stuff to finally support my ideas

Have a great day I must get back to the Lab
alex

Unfortunately any gravitational push theory violates the principle of equivalence, that states that gravitational mass and inertial mass are the same.

Try performing Einstein's elevator experiment in the gravitational "shadow" between two bodies that are being pushed towards each other.

Regards

Steven
http://users.westconnect.com.au/~sjastro/small

[xelasnave]

Thanks for the opportunity to consider something specific Steven.
Maybe I am missing something but I fail to see there need be any problem in the areas you suggest.
Let me think about it.
Thanks this is very exciting.
alex

[xelasnave]

To think one must focus on the issue.. and so I state the equivalence principle that would be the foundation of General Relativity.

It states that ``there is no experiment a person could conduct in a small volume of space that would distinguish between a gravitational field and an equivalent uniform acceleration''

I lifted the following and changed it slightly so as not to infringe copyright...



Consider two elevators ..you in one and one``at rest'' outside your elevator way out in space.. the other traveller shines a flashlight horizontally into your elevator and toward the far wall of the elevator.

At rest, then you will see the beam of light travel in a straight horizontal line.

If your elevator is moving at a constant velocity upward relative to the other elevator the beam of light shall travel in a straight-line path angled downward.

The other person sees the beam travelling in a horizontal direction.

If the elevator is accelerating upward the beam will follow a curved path downward relative to you.

If the beam of light curves in the accelerating elevator, then the equivalence principle says that the beam of light should also follow a curved path in a gravitational field.


So this what we face!!!

Personally I question the experiment...it is a thought experiment and clearly if we conducted such an experiment I wonder what "bend" in the light path one could actually observe...lets say our elevator is 12 feet wide and so our beam is that length... at what rate of acceleration could we detect a upward or downward trend in the beam... light travels 300,000 klms per second... to cover a distance of 12 feet we can determine but even without the sums I suspect any variance would be impossibvle to detect.... I wonder if the elevator was doing near light speed could we get a readng...maybe? ..in theory because in reality the elevator will never whislt humans are trying to move it get to a speed within a small fraction of the speed of light....

IT is a thought experiment... so facts the we seize upon issuing in our belief from this thought experiment must keep such in mind....

So Steven I have thought about how push gravity can offend the premise I can not... and so I must ask of you specifically where you see a difficulty say if we seek to establish the "observed" facts within a context of a push gravity approach...

I am sorry to have to ask but I am clearly missing something and although embarrassed because of my ignorance must ask you to point out what you feel could deal a lethal blow to push gravity.


alex

[xelasnave]

I have tried the experiment in the shadow as you suggest ..at first run seems ok but I will think more and get back here with my thoughts.
alex

[sjastro]

Originally Posted by xelasnave

So Steven I have thought about how push gravity can offend the premise I can not... and so I must ask of you specifically where you see a difficulty say if we seek to establish the "observed" facts within a context of a push gravity approach...

I am sorry to have to ask but I am clearly missing something and although embarrassed because of my ignorance must ask you to point out what you feel could deal a lethal blow to push gravity.

alex

Hello Alex,

I'm not into debunking any theory.

Particles colliding into larger bodies as a mechanism for push gravity only requires the inertial mass of the body to be defined.

One of the early criticisms of push gravity theory is that the gravitational mass seemed to play no role what so ever. The size of the gravitational shadow in conjunction with colliding particles overcoming the inertia of each body determined the gravitational effects.

This clearly violated both GR and Newtonian physics.

One way of bringing gravitational mass into the picture was by eliminating the shadow effect. Particles were allowed to penetrate each body. Some of the particles would undergoe inelastic collisions. The change in KE before and after collision allowed bodies to move towards each other.

The main question now is what has happened to the converted energy? Has been converted to heat, has mass accretion occurred or both. There is no supportive evidence.

Regards

Steven

[xelasnave]

Thanks for your views Steven.

You asked....
The main question now is what has happened to the converted energy?

Well that is a good question... in the case of the Sun it converts into the Corona as I said above the out flow runs into the "gravity" flow ... now these particles travel at near C and although of little mass can produce a lot a energy ..via the famous equation...I think the Corona gets its energy this way...


I have thought that maybe it is the missing energy you enquire about that "powers" an atom.... when you think of it atoms seem to carry infinite energy in so far as they last a very long time for such a small item...where do they hide their power pak???... maybe their energy is being topped up by the flow??? maybe they get energy from the interaction with the "flow" (the gravity push stuff).... maybe the electrons orbit because every time a particle from the flow hits them they are kicked along.....

Like wind driving a windmill.....mind you this idea may need a little more support than that given here

I thank you for engaging in such deep matters..
have a great day
alex

[sjastro]

Originally Posted by xelasnave

Thanks for your views Steven.

You asked....
The main question now is what has happened to the converted energy?

Well that is a good question... in the case of the Sun it converts into the Corona as I said above the out flow runs into the "gravity" flow ... now these particles travel at near C and although of little mass can produce a lot a energy ..via the famous equation...I think the Corona gets its energy this way...alex

While the high temperatures of the Corona has never been satisfactory explained, the dimensions of the Corona vary according to the solar cycle. I can't see why the Corona dimensions would vary if it is caused by the inelastic collisions between gravitational particles and the sun.

Regards

Steven

[Karls48 (Karl)]

Equivalence principle experiment using the elevator as example is flawed for at least two reasons. Such a thought experiments belongs to the human thought domain and human imagination and got very little to do with actual physical reality.
If you are put in the elevator in under influence of gravitational field you will experience gravity imminently. However if the equivalent weight of you (apparent gravity) is due to the acceleration, such an apparent gravity will build over the period of time. As far we know no mass can accelerate from 0 to n speed in instant. Therefore you would know if the apparent gravity you are experiencing is due to acceleration or gravity.

If by some magical means (ala Scotty beam me up) you can be put in the elevator that is already under influence of either gravitational field or acceleration (what happen to causality?), then over the period of time if you are under influence of gravitational field (orbiting a star) your weight will remain constant. However if your apparent gravity is due to the acceleration, you will eventually come to gravitational field of some star somewhere in the universe. Then you can measure acceleration or de-acceleration due to the gravitational influence of such a star.

Now here comes fudge factor. People who will disagree with this will say, “if there are not any stars”, “if you can get to the elevator that is already under influence of gravity or acceleration”. My answer to this is that what my grandma used to tell me when I started with IF. “If you could catch fish on the road you would not need to go the river”.

Alex’s assumptions regarding space and the aether seems to display a lot of thought or intuition. If we assume that Big Bang theory is correct and the space and the time was created at moment of Big Bang, it is very reasonable to assume that the space is just some kind of conversion of matter or energy. The time itself is not real physical entity being just property of the space. This would explain the problem of electromagnetic waves propagating via medium without any substance. It may even provide answer to dark matter assumption, the dark matter being the space itself.

Again I have to point out that this tread started with link to the article that presents good arguments for speed of gravity being faster then speed of light. So far no one presented any reasonable argument as why it cannot be. The only answer seems to be that nothing can travel faster then light – why? Because Einstein say so.

[skwinty (Steve)]

Originally Posted by Karls48

Again I have to point out that this tread started with link to the article that presents good arguments for speed of gravity being faster then speed of light. So far no one presented any reasonable argument as why it cannot be. The only answer seems to be that nothing can travel faster then light – why? Because Einstein say so.

Hi Karl
Herewith a post by Hans de Vries with regard to this issue.
Also remember, as I have said before, Einsteins postulates have been tested and verified many times over and until they can be disproved or some other theory has the same credentials then Einsteins postulates remain valid and relevant. It seems as though you have some doubt regarding Einstein.

Tom Van Flandern also claims that mars was inhabited by humans or human like beings....

Maybe you understand why your link (to his website) was removed. As far as the 1998
paper concerns, it is wrong. It has been discussed here multiple times as well as on
sci.physics.research (with Steve Carlip and John Baez)


Where does Tom Van Flandern go wrong?

He assumes that the direction of the force, gravitational or electric, is always pointing
to the place where the source was at the moment that the force field was emitted.

This assumption, as we now know more than a century (!), is wrong. The Electric Field
of a moving charge points to the place where the charge will be if it continuous
moving in the same direction during the time the force field needs to propagate.

The same is true for gravitation. In practice this means for the dynamics of the solar
system that the force is towards the location where the planet or sun is at that moment.

This can be measured and Van Flandern erroneously concluded that this means that
gravity must be instantaneous. Because the force is directed to the location where
the object is and not to where it was. His conclusion is a beginners error which
unfortunately made it into a peer reviewed journal.


For the math in case of the electric field, see for instance the links to my book in the
post I made on this thread here.