Is Gravity timelessly constant? Or can it change?

Hello Landon,

Personally do not know. Cool thoughts and ideas however.

Just two pieces of information that might be useful to know:

Gravitational force decreases proportionately to the squared distance (~d²) and becomes immeasurable quite quickly in the distances of our universe.

The change of a gravitational force "moves" with the speed of light. If there is a change in gravitation 2000 light years away from us it will take 2000 years until we can measure it here on earth.

Landon Caeli said:

Say that spacetime runs into a hypothetical brick wall at the outer limits of the universe... Will it then begin to expand inward towards matter, having nowhere else to go, essentially squashing planets into tiny specks..?

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Space itself is expanding. If there is a brick wall at the "edge" of space it will expand as well.
Outside of space there is no space - where there is no space there is no space for a brick wall to expand into.
I think the only way to "crash into a brick wall" is the case where a brick wall suddenly appears at the edge of space and does not expand as well - but 1) then only galaxies and such will crash, not spacetime itself, and 2) the nature of space's expansion does not allow that to happen, since the universe is expanding as a whole and not at the edges only. Imagine you pull apart a yeast dough. If there is something solid inside it will move outwards as well.

Landon Caeli said:

I wonder if any scientist has tested whether gravity pressure increases, or decreases across time. One hypothetical reason gravity might increase, is that there is less sparatic pieces of matter floating around in the universe.

So it could be possible that gravity is not constantly the same on a planet like earth, depending on what goes on elsewhere in space.

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Sparatic?

OB

There is no such thing as "gravity", it is the force of dark matter pressing on all physical objects.

Landon Caeli said:

Sure. As planets, moons and gas giants are consistently consumed by their respective black holes over time, it could disrupt the pressure of space pushing on our planet (gravity).

Also, if space is expanding, perhaps the pressure of space against our planet decreases in strength, as spacetime gets stretched thinner.

...Just potential possibilities. Who knows?

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Sorry Landon. I wasn't querying the science - just the word 'sparatic'.

OB

Landon Caeli said:

I wonder if any scientist has tested whether gravity pressure increases, or decreases across time.

Click to expand...

The strength of gravity is represented by the gravitational constant G, as in Newton's law of gravitational force between two objects equals the constant times the two masses, divided by the square of the distance between them: F=GmM/r^2

There have been various tests to see whether G is actually constant or not. This one shows that G is pretty darn constant. "We find that only those solar models constructed with (1/G)dG/dt 1.6 × 10-12 yr-1 are consistent with the observations."

In other words, the strength of gravity changes by no more than 1 part in a trillion in a year. (And as far as we know, it really is constant.)

Landon Caeli said:

I wonder if any scientist has tested whether gravity pressure increases, or decreases across time. One hypothetical reason gravity might increase, is that there is less sporadic pieces of matter floating around in the universe.

So it could be possible that gravity is not constantly the same on a planet like earth, depending on what goes on elsewhere in space.

Click to expand...

I don’t normally look at this area of the forum; I accidentally scrolled down and saw this post.

There is a theory called “expanding earth model” that states the force of gravity was much less on earth in the past. I’m not convinced this theory is correct and I’m not endorsing it in any way so I’ll just share what some of the arguments are for the earth having less gravity in the past.


Elephants have to eat 16 to 18 hours per day to survive; using similar metrics if a Brontosaurus was alive today it would have to eat 90 to 180 hours per day.

13 ton Mamenchisaurus would have to eat 1,150 pounds of vegetation per day, this would destroy our current eco system.

Due to the principles of gravity, mass, and the limitations of muscular anatomy in any life form, it would be impossible for any animal weighing more than approximately 20,000 pounds to be able to lift its own weight on land.

A giraffe has higher blood pressure than any other animal to get blood through its neck (approximately 280/180). The blood pressure that would be required for the largest dinosaurs would rupture their arteries.

Pterosaurs would have to have far larger wing spans to support their weight in flight.

Landon Caeli said:

I wonder if any scientist has tested whether gravity pressure increases, or decreases across time. One hypothetical reason gravity might increase, is that there is less sporadic pieces of matter floating around in the universe.

So it could be possible that gravity is not constantly the same on a planet like earth, depending on what goes on elsewhere in space.

Click to expand...

When I was in college a lab to determine the gravitational constant was included as part of the first years physics majors classes.

So effectively yes. Labs get rerun all the time and any drift would be noticed. Also any change would have an effect on the orbits of all the planets and moons. All of which are plotted all the time and any change would be noticed.

Do you mean to ask if the gravitational constant can change? So far there's no evidence of it but it could be possible.

Twenty years ago as then director of an astroscience company, I recollect seeing a paper in which someone argued that the speed of light has gradually changed over time. A plausibility argument. It made some problems harder, others easier, in terms of eg cosmo constants, rotation of galaxies, age of universe. missing matter energy etc. It was an interesting idea. With massive ramifications. Forget the name of who wrote it. It disappeared into obscurity,

The establishment did what it normally does. Called it bunk. ( but then you would not believe how rude professors often are to each other at conferences, so this guy stood not a chance - the normal question at a conference "is the presenter does realise he is an idiot" because...).

But science should think the unthinkable more than it does.
It is after all just a model of what we perceive of the universe. If the equations fit observations better, good on them. Who knows what it actually "is".

Landon Caeli said:

I wonder if any scientist has tested whether gravity pressure increases, or decreases across time. One hypothetical reason gravity might increase, is that there is less sporadic pieces of matter floating around in the universe.

So it could be possible that gravity is not constantly the same on a planet like earth, depending on what goes on elsewhere in space.

Click to expand...

Mountainmike said:

Twenty years ago as then director of an astroscience company, I recollect seeing a paper in which someone argued that the speed of light has gradually changed over time. A plausibility argument. It made some problems harder, others easier, in terms of eg cosmo constants, rotation of galaxies, age of universe. missing matter energy etc. It was an interesting idea. With massive ramifications. Forget the name of who wrote it. It disappeared into obscurity,

The establishment did what it normally does. Called it bunk. ( but then you would not believe how rude professors often are to each other at conferences, so this guy stood not a chance - the normal question at a conference "is the presenter does realise he is an idiot" because...).

But science should think the unthinkable more than it does.
It is after all just a model of what we perceive of the universe. If the equations fit observations better, good on them. Who knows what it actually "is".

Click to expand...

The possibility of the physical 'constants', including the speed of light, varying has been seriously considered by numerous researchers, and is still an open question. Most physicists are sceptical because the hypotheses are speculative and there is insufficient data to support them.

FrumiousBandersnatch said:

The possibility of the physical 'constants', including the speed of light, varying has been seriously considered by numerous researchers, and is still an open question. Most physicists are sceptical because the hypotheses are speculative and there is insufficient data to support them.

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Or perhaps in absence of compelling evidence to the contrary Occam’s razor was applied in a situation where evidence for constancy is equally uncompelling, but calculation is made so much easier!

Mountainmike said:

Or perhaps in absence of compelling evidence to the contrary Occam’s razor was applied in a situation where evidence for constancy is equally uncompelling, but calculation is made so much easier!

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The default is to assume constancy unless there is good reason (evidence) to think otherwise.