Does gravity attract masses in space, or does it curve space between them?

  • 55 Replies
  • 5417 Views

0 Members and 1 Guest are viewing this topic.

*

Offline Alan McDougall

  • Neilep Level Member
  • ******
  • 1285
    • View Profile
Does gravity attract masses in an existing space, or does it curve the space between them?

The answer to this question is much more complex than meets the eye?
The Truth remains the Truth regardless of our beliefs or opinions the Truth is always the Truth even if we know it or do not know it (The Truth remains the Truth)

*

Offline jeffreyH

  • Global Moderator
  • Neilep Level Member
  • *****
  • 4058
  • The graviton sucks
    • View Profile
Since we know that time dilation exists then at least one of the components of spacetime is affected. If we are to assume the validity of Lorentz transformations then space must also be affected. If somehow the Lorentz transformations are incorrect as regards the spacial component then a reassment of general relativity would be necessary. Although I don't see how this can be.

*

Offline IAMREALITY

  • Sr. Member
  • ****
  • 275
    • View Profile
Be honest... Do you just search quora for topics to post? Lol

The answer is b. It's due to the curvature of spacetime. Like occams razor dictates... The simplest explanation usually is the right one...  Far easier an explanation to say an object is just continuing in a straight path around a curved surface than the mechanisms necessary for the attraction explanation...

*

Offline agyejy

  • Sr. Member
  • ****
  • 211
    • View Profile
Be honest... Do you just search quora for topics to post? Lol

There was a day awhile back that I noticed at least 3 of Alan's topics were straight copy pastes from quora. I don't visit quora enough to know for sure but if I noticed that many the actual number must be significant. Other question and answer sites could also be providing material.

*

Offline JohnDuffield

  • Sr. Member
  • ****
  • 490
    • View Profile
Does gravity attract masses in an existing space, or does it curve the space between them?
A concentration of energy in the guise of a massive star "conditions" the surrounding space, altering its properties. This effect diminishes with distance in a non-linear fashion, and is modelled as curved spacetime. Note though that curved spacetime is not curved space and curved time. Instead it's space that is "neither homogeneous not isotropic". When you plot this inhomogeneity, your plot is curved. And you plot it with measuring devices such as clocks at different altitudes, so your metric is curved. But space isn't. 

*

Offline jeffreyH

  • Global Moderator
  • Neilep Level Member
  • *****
  • 4058
  • The graviton sucks
    • View Profile
Does gravity attract masses in an existing space, or does it curve the space between them?
A concentration of energy in the guise of a massive star "conditions" the surrounding space, altering its properties. This effect diminishes with distance in a non-linear fashion, and is modelled as curved spacetime. Note though that curved spacetime is not curved space and curved time. Instead it's space that is "neither homogeneous not isotropic". When you plot this inhomogeneity, your plot is curved. And you plot it with measuring devices such as clocks at different altitudes, so your metric is curved. But space isn't.

You could actually learn this properly and be able to use the correct terms. Once you do this you might actually be able to start helping others by properly answering their questions. Give it a try John.

*

Offline jeffreyH

  • Global Moderator
  • Neilep Level Member
  • *****
  • 4058
  • The graviton sucks
    • View Profile
I have  a question for you John. It is not difficult and I don't mind if you look the answer up. What is the definition of a metric?

*

Offline puppypower

  • Hero Member
  • *****
  • 573
    • View Profile
Wouldn't a curved path create centrifugal force thereby cancelling out some of the gravity vector? One can see this affect with satellites orbiting the earth so they never are able to meet. The moon and earth attract by gravity yet they can never close the deal, due to a curved path.

Although, asteroids which hit have hit the earth, originally follow their own curved paths as they orbit the sun. These collide more out of being in the right place at the right time, compared to direct gravity affect between earth and asteroid. 

If we assume curved path, as the two objects gets closer and closer and therefore gravity gets stronger, does the path curve more and more as the space-time well gets deeper? If this was true, to be logically consistent, does this mean that things falling into a black hole take forever to reach the core, due to tighter and tighter orbits, until it becomes a centrifugal based satellite? It may never reach the core if it orbits, therefore the ideal of the singularity may take forever.



 

*

Offline Thebox

  • Neilep Level Member
  • ******
  • 3211
    • View Profile
Well I do not think Einstein actually said space was curved in anyway but rather space-time was curved, so I suppose the answer to your question depends on how we interpret space-time.

If we considered that space-time only exists between masses  then orbital motion would suggest that in some way the space-time was ''spiralling'' and a torque was produced between masses that curved the forces between the masses.



Mass attracts mass, gravity is what we call the force,


Does the space curve? there is no evidence of this

Does the ''invisible'' forces between masses curve?  probably but we can't ''see'' it.


*

Offline IAMREALITY

  • Sr. Member
  • ****
  • 275
    • View Profile
Be honest... Do you just search quora for topics to post? Lol
There was a day awhile back that I noticed at least 3 of Alan's topics were straight copy pastes from quora. I don't visit quora enough to know for sure but if I noticed that many the actual number must be significant. Other question and answer sites could also be providing material.
It was just an observation I couldn't avoid.  I really was just being lighthearted though.  But his reply. Wow. Lol.

On Edit:  Might as well reply here instead of disrupting the conversation that has since taken place downthread...

So what! "This was the result of  IAMREALITY who is on my ignore list trying to make trouble by proxy, because he cannot get at me directly with his insults"
Ummm, no.  This was simply a lighthearted observation, which turned out to actually be true.  It wasn't an insult at all.  You really need to lighten up dude. 

And the main part of my post was actually replying to your thread.  Why?  Cause it's a thread.  And the whole point is to have replies in them. 
Quote
Although I no longer look at anything IAMREALITY posts, he continues to follow everything I post, and invade all of my threads and makes comments "in all of them" in an ongoing effort to demean me in anyway he can.

Don't flatter yourself.  I do not 'follow' you at all.  But when half of the threads are started by you, it kinda makes it impossible to not reply to some of them; especially when there are only so many new threads generated on this site each day to begin with.  Do I reply to all of them?  Ummmm nope!  And I don't 'invade' your threads.  I reply within them, like anyone else does.  Why?  Because I don't suffer from this irrational and nonsensical vendetta that you have.  Instead, you're a poster like anyone else.  If I see a thread and feel the need to reply, I reply, period.  That's like, ya know, what people do here and stuff.
Quote
He has proved a disruptive influence on the forum since the sad day he joined and almost never starts a thread of his own or asks anything of interest himself.
There ya go with the personal attacks again.  And all this because of a lighthearted comment.  I'd wager your attacks and constant replies to me outside of the context of my posts is what has been disruptive.  Otherwise I'm the same as any other poster here, and I've disrupted nothing.  In fact, in the last few days I've seen you attack many other posters as well, with direct personal attack.  I've seen you post religious mumbo jumbo and a bunch of other spam like nonsense.  Do you think people came to a scientific forum to be preached religion?  Do you think they came here for your lengthy poetry?  No, they didn't.  And I have posted threads and will do more when I see fit.  I've also asked several things of interest within threads.  Just because you choose to cherry pick what you see is your problem not mine.
Quote
He was simply using you to get at me, who he despises! 
First of all, how could I use someone to get to you, when I replied directly to you, and it was the other poster who replied to me?  How does that even remotely make sense?  Second of all, I despise no one.  Again, you're projecting.  Your constant irrational personal attacks on me have shown you to be the one who despises.  As far as my perspective, I literally couldn't care less.  You're an anonymous poster on a forum.  If you reply to me I'll reply back with logical rebuttal.  Same as any other poster.  The reason things get derailed with our interaction is directly related to your inability to reply to the context of my replies but instead choosing the path of irrational personal attacks instead.  But again, as far as I'm concerned, you're nothing more than a poster just like anyone else.  You're trying to insinuate that I have this vendetta against you, that I seek you out, that I'm focused on you.  But that's utter nonsense.  There's only one here with an irrational vendetta, and it ain't me...  I ask you yet again, for the umpteeth time, please avoid personal attacks and stick to the context of my posts only.  Thanks.

And I'm sorry to those in this thread that need to read all this nonsense.  I know it's not what you came here for.  But when I'm personally attacked like that I can't avoid defending myself.  But I'll limit saying what I need to say in one post only (in this case, this one) and give my word I will not go back and forth if there are additional attacking replies.  Carry on...

« Last Edit: 29/06/2016 16:26:23 by IAMREALITY »

*

Offline jeffreyH

  • Global Moderator
  • Neilep Level Member
  • *****
  • 4058
  • The graviton sucks
    • View Profile
Well I do not think Einstein actually said space was curved in anyway but rather space-time was curved, so I suppose the answer to your question depends on how we interpret space-time.

If we considered that space-time only exists between masses  then orbital motion would suggest that in some way the space-time was ''spiralling'' and a torque was produced between masses that curved the forces between the masses.



Mass attracts mass, gravity is what we call the force,


Does the space curve? there is no evidence of this

Does the ''invisible'' forces between masses curve?  probably but we can't ''see'' it.

Sometimes you actually impress me and this is one of those times.

*

Offline Thebox

  • Neilep Level Member
  • ******
  • 3211
    • View Profile
Well I do not think Einstein actually said space was curved in anyway but rather space-time was curved, so I suppose the answer to your question depends on how we interpret space-time.

If we considered that space-time only exists between masses  then orbital motion would suggest that in some way the space-time was ''spiralling'' and a torque was produced between masses that curved the forces between the masses.



Mass attracts mass, gravity is what we call the force,


Does the space curve? there is no evidence of this

Does the ''invisible'' forces between masses curve?  probably but we can't ''see'' it.

Sometimes you actually impress me and this is one of those times.

Congrats on becoming a moderator Jeff, I noticed yesterday .


If we take a look at an equilibrium of forces and describe this as an absolute linearity, then applied centripetal force by both masses at each ''end'' of the linearity on each other, then the linearity of the equilibrium force would surely curve under the gravitational pressure?


A sort of stress curvature of the ''invisible'' linearity of forces.




*

Offline Alan McDougall

  • Neilep Level Member
  • ******
  • 1285
    • View Profile
Well I do not think Einstein actually said space was curved in anyway but rather space-time was curved, so I suppose the answer to your question depends on how we interpret space-time.

If we considered that space-time only exists between masses  then orbital motion would suggest that in some way the space-time was ''spiralling'' and a torque was produced between masses that curved the forces between the masses.

Mass attracts mass, gravity is what we call the force,


Does the space curve? there is no evidence of this

Does the ''invisible'' forces between masses curve?  probably but we can't ''see'' it.

Sometimes you actually impress me and this is one of those times.

I fail to see how that impressed you?

https://www.thestar.com/news/insight/2012/08/18/einstein_discovered_that_gravity_is_not_a_force_but_a_curvature.html

Excerpt

Max Planck, himself a leading German physicist, advised Einstein to abandon his quest for this grander theory of relativity, for he was bound to fail.

But by 1916, Einstein had succeeded.

The resulting depiction of gravity was stunningly different from the orthodox view that had prevailed since the time of Sir Isaac Newton, who first devised a coherent explanation of the phenomenon, one that accounted for the behaviour of familiar objects on Earth as well as the interaction of planets and stars.

Up to a point.

The classical theory of gravity had been a huge breakthrough in its time, and it still provides a good means of predicting the motion of objects. But it is wrong, in part because Newton misunderstood what gravity is.

He considered gravity to be a force that objects exert upon each other.

But?

'But, in a burst of brilliance, Einstein realized that no such force is required and in fact no such force exists.'

We “feel” the force of gravity only because we are perched upon a surface that gives us weight. Remove that surface and gravity would no longer feel like anything at all.

We would be weightless.

By this way of reckoning, the Earth only seems to be turning in circles around the sun. In fact, it is going straight, but straight along a space-time surface that is itself curved — warped by the mass of the sun.

If this seems to make no sense, imagine driving “straight” from Toronto to Montreal. The truth is, you can’t do it, not even on the 401. The “straightest” route between the two cities — in fact, any route between the two cities — is curved by the surface of the Earth. In fact, if it goes on long enough, any “straight-line” journey along the surface of the Earth will eventually describe a circle.
The same goes for any “straight-line” journey in the vicinity of the sun.

“Newton would have said that an apple fell to Earth because there was a mutual force of gravitational attraction,” writes Simon Singh in his book Big Bang . “But Einstein now felt that he had a deeper understanding of what was driving this attraction: the apple fell to Earth because it was falling into the deep hollow in space-time caused by the mass of the Earth.”

Although it might not seem like it, the Earth is right now falling into the even deeper hollow in space-time caused by the mass of the sun. The only thing preventing a collision is the Earth’s velocity, which is about 107,000 km/h relative to the sun, or just enough to ensure that, in its never-ending downward spiral toward the fiery centre of the planetary system, our fine blue orb keeps missing its target — fortunately for us.

This constant state of free fall, coupled with an appropriate velocity, is what constitutes an orbit.
Astronauts aboard the orbiting International Space Station appear to be weightless — in fact, they are weightless — but not because they have escaped the reach of the Earth’s gravity. Instead, they and their space station are in a state of free fall toward the Earth.

They avoid striking the planet for the same reason the Earth doesn’t crash into the sun — because they are going pretty fast. The space station travels at about 19,000 km/h relative to the Earth, or just enough to prevent a collision.

But the important point for relativity theory is that space-time is curved by mass.

“A star or a planet or any hunk of mass warps space and time,” says Robert Mann, a physicist at the University of Waterloo.

This may sound bizarre, but it is true


« Last Edit: 29/06/2016 15:13:19 by Alan McDougall »
The Truth remains the Truth regardless of our beliefs or opinions the Truth is always the Truth even if we know it or do not know it (The Truth remains the Truth)

*

Offline Thebox

  • Neilep Level Member
  • ******
  • 3211
    • View Profile
The problem with saying that objects displace space is that we would then have to prove space is made of substance.


A while back I came up with a balloon situation and in this situation we start off with a deflated balloon and create an imaginary line of two points, A and B,

[tex]\rightharpoon\atop{ab}[/tex]

Within this line is the deflated balloon ''sitting'' at the half way point.


A...............Balloon.................B


We then inflate the balloon to reveal the points end up inside the balloon

Balloon...A...........................................B........Balloon.


The question was does the space pass through the balloon or does the balloon displace the space.


We know the Balloon displaces the air around it but we do not know the question asked .


However we do know that objects attract objects by something that is in the object being a mechanism for gravity.

The Cavendish experiment showing this and the obviousness of that things are held together by something.
« Last Edit: 29/06/2016 15:30:28 by Thebox »

*

Offline IAMREALITY

  • Sr. Member
  • ****
  • 275
    • View Profile
Well I do not think Einstein actually said space was curved in anyway but rather space-time was curved, so I suppose the answer to your question depends on how we interpret space-time.

If we considered that space-time only exists between masses  then orbital motion would suggest that in some way the space-time was ''spiralling'' and a torque was produced between masses that curved the forces between the masses.

Mass attracts mass, gravity is what we call the force,


Does the space curve? there is no evidence of this

Does the ''invisible'' forces between masses curve?  probably but we can't ''see'' it.

Sometimes you actually impress me and this is one of those times.

I fail to see how that impressed you?

https://www.thestar.com/news/insight/2012/08/18/einstein_discovered_that_gravity_is_not_a_force_but_a_curvature.html



You misunderstood the context possibly.

The original poster was not saying einstein didn't say spacetime wasn't curved.  In fact, the poster directly stated that he did.

Instead, the poster was referring to merely space, as space.  Because you had asked if the space between the objects is curved instead of using the proper terminology of spacetime.  So it was a good pickup by the poster and good reply.
« Last Edit: 29/06/2016 16:29:47 by IAMREALITY »

*

Offline IAMREALITY

  • Sr. Member
  • ****
  • 275
    • View Profile
The problem with saying that objects displace space is that we would then have to prove space is made of substance.


A while back I came up with a balloon situation and in this situation we start off with a deflated balloon and create an imaginary line of two points, A and B,

[tex]\rightharpoon\atop{ab}[/tex]

Within this line is the deflated balloon ''sitting'' at the half way point.


A...............Balloon.................B


We then inflate the balloon to reveal the points end up inside the balloon

Balloon...A...........................................B........Balloon.


The question was does the space pass through the balloon or does the balloon displace the space.


We know the Balloon displaces the air around it but we do not know the question asked .


However we do know that objects attract objects by something that is in the object being a mechanism for gravity.

The Cavendish experiment showing this and the obviousness of that things are held together by something.

How can spacetime be displaced by anything, since technically if it was displaced time would cease for all the particles in the object (suspend your disbelief in time for a moment) if that were true?   Wouldn't spacetime, though curved, still need to be present within any given mass?
« Last Edit: 29/06/2016 15:47:16 by IAMREALITY »

*

Offline IAMREALITY

  • Sr. Member
  • ****
  • 275
    • View Profile

Sometimes you actually impress me and this is one of those times.

Congrats on becoming a moderator Jeff, I noticed yesterday .

Oh wow I just noticed too!  Congrats man!  And best of luck to you in that role!  Moderators are the most unappreciated folk on the entire web hahaha

*

Offline Thebox

  • Neilep Level Member
  • ******
  • 3211
    • View Profile
The problem with saying that objects displace space is that we would then have to prove space is made of substance.


A while back I came up with a balloon situation and in this situation we start off with a deflated balloon and create an imaginary line of two points, A and B,

[tex]\rightharpoon\atop{ab}[/tex]

Within this line is the deflated balloon ''sitting'' at the half way point.


A...............Balloon.................B


We then inflate the balloon to reveal the points end up inside the balloon

Balloon...A...........................................B........Balloon.


The question was does the space pass through the balloon or does the balloon displace the space.


We know the Balloon displaces the air around it but we do not know the question asked .


However we do know that objects attract objects by something that is in the object being a mechanism for gravity.

The Cavendish experiment showing this and the obviousness of that things are held together by something.

How can spacetime be displaced by anything, since technically if it was displaced time would cease for all the particles in the object (suspend your disbelief in time for a moment) if that were true?   Wouldn't spacetime, though curved, still need to be present within any given mass?


Yes space-time is present in all mass if we consider that mass if the summation of all energies and forces within an objects volume .  Without space-time you would be a dense dormant ''rock'' with no ''life''(energy).  I consider space-time on a deeper understanding could be ''light'', because if it were not for ''light'' I am sure an objects entropy would soon dissipate it's energy into space and be a ''dead'' object.

*

Offline PmbPhy

  • Neilep Level Member
  • ******
  • 2788
    • View Profile
Quote from: Alan McDougall
Does gravity attract masses in an existing space, or does it curve the space between them?

It depends. If you have to point masses then the spacetime is curved and the space between the two objects is also curved. However the presence of spacetime curvature or spatial curvature is not necessary to exist for there to be a gravitational force acting on an object. was that more complicated than met your eyes? :)

Quote from: Alan McDougall
The answer to this question is much more complex than meets the eye?
You're asking a question that you already know the answer to? That makes it more of a rhetorical question, does it not?

*

Offline puppypower

  • Hero Member
  • *****
  • 573
    • View Profile
Gravity is an acceleration, with acceleration d/t/t. If you do a dimensional analysis, acceleration due to gravity is one part distance, d, and two parts time, t. Or the acceleration due to gravity is space-time, plus time. What is bending or curving space-time d-t, is connected to time; t.

With special relativity, space-time does not curve, since SR is due to velocity, which is d/t. This does not contain the extra time dimension associated with acceleration.

There is evidence of this which has existed since the 1820's. In photography there is an affect called motion blur. Motion blur occurs when the shutter speed is slower than the action speed. Since a still picture stops time, the difference in speed appears as uncertainty in distance; motion blur. If you look at the picture below, one gets the impression of motion, even with time stopped. The brain interprets the uncertainty in distance, as motion; d/t*, even though time has stopped. Time is conserved in the motion blur.

If we go back to gravity and acceleration, it is space-time plus time, (d-t, t). If we add the motion blur, where the time potential is converted to distance potential, acceleration can also become two layers of space-time; space-time plus (t=space-time)* .

The motion blur analogy of space-time or (space-time)* is an artifact of our quantum universe. Time is not continuous in a quantum universe but needs to follow quantum steps. When time jumps between quanta, time has stopped and uncertainty in distance appears.  When time is in focus, then time creates acceleration in space-time. 



 
« Last Edit: 29/06/2016 16:47:06 by puppypower »

*

Offline Alan McDougall

  • Neilep Level Member
  • ******
  • 1285
    • View Profile
Quote from: Alan McDougall
Does gravity attract masses in an existing space, or does it curve the space between them?

It depends. If you have to point masses then the spacetime is curved and the space between the two objects is also curved. However the presence of spacetime curvature or spatial curvature is not necessary to exist for there to be a gravitational force acting on an object. was that more complicated than met your eyes? :)

Quote from: Alan McDougall
The answer to this question is much more complex than meets the eye?
You're asking a question that you already know the answer to? That makes it more of a rhetorical question, does it not?

Was my saying it was more complex than means the eye true or false, don't read into my statements something that is not there??

"I do not know the answer", but "what I do know"from reading about this topic "is that this issue that it is complex" and that the answer is complex and has been widely debated by better minds than mine and I am curious and would like to be informed and learn from people like you, who are much more knowledgeable than I am.

You should not just assume things I did not mean. I have emphasized on more than one occasion that I am not a physicist or a mathematician, I am a humble very curious Engineer, trying to broaden my understanding in the sciences of which I have a basic comprehension. However, in Engineer we have to use math and physics as tools in our jobs.

"You know this Pete and your comment was uncalled for"!

Edited and unnecessary underlining removed by me (Alan)

Alan
« Last Edit: 30/06/2016 00:14:08 by Alan McDougall »
The Truth remains the Truth regardless of our beliefs or opinions the Truth is always the Truth even if we know it or do not know it (The Truth remains the Truth)

*

Offline jeffreyH

  • Global Moderator
  • Neilep Level Member
  • *****
  • 4058
  • The graviton sucks
    • View Profile
Can we have a little decorum please. Challenge the ideas not the personalities.

*

Offline Alan McDougall

  • Neilep Level Member
  • ******
  • 1285
    • View Profile
Can we have a little decorum please. Challenge the ideas not the personalities.

I see nothing wrong with my response to Pete, it was a polite and attempt to put right a misconception that I knew the answer because, I said it the answer was complex.?

In no way could the question I posed in this tread of mine be taken as a personal rhetorical question of which I knew the answer!
The Truth remains the Truth regardless of our beliefs or opinions the Truth is always the Truth even if we know it or do not know it (The Truth remains the Truth)

*

Offline IAMREALITY

  • Sr. Member
  • ****
  • 275
    • View Profile
Can we have a little decorum please. Challenge the ideas not the personalities.

I see nothing wrong with my response to Pete, it was a polite and attempt to put right a misconception that I knew the answer because, I said it the answer was complex.?

In no way could the question I posed in this tread of mine be taken as a personal rhetorical question of which I knew the answer!

For sake of being up front, he was referring to our war, and triggered by my objection to your calling out Pete by saying what he said was uncalled for when it was benign and perfectly fine.  Though there was more, and it was written matter of factly, I won't get into it cause that's not the point of this post. The point was for sake of defending the mod and setting it straight, since I didn't consider at the time that deleting my post since the back and forth wasn't worth it, would end up causing Jeffrey's message to lose context.  So I figured I'd come forward. Anyway, let this thread move on now.  Thanks

*

Offline Alan McDougall

  • Neilep Level Member
  • ******
  • 1285
    • View Profile
Can we have a little decorum please. Challenge the ideas not the personalities.

I see nothing wrong with my response to Pete, it was a polite and attempt to put right a misconception that I knew the answer because, I said it the answer was complex.?

In no way could the question I posed in this tread of mine be taken as a personal rhetorical question of which I knew the answer!

For sake of being up front, he was referring to our war, and triggered by my objection to your calling out Pete by saying what he said was uncalled for when it was benign and perfectly fine.  Though there was more, and it was written matter of factly, I won't get into it cause that's not the point of this post. The point was for sake of defending the mod and setting it straight, since I didn't consider at the time that deleting my post since the back and forth wasn't worth it, would end up causing Jeffrey's message to lose context.  So I figured I'd come forward. Anyway, let this thread move on now.  Thanks

It takes at least two to engage in a war and two to make peace, this is my attempt to make peace and move on!

Best Regards

Alan
The Truth remains the Truth regardless of our beliefs or opinions the Truth is always the Truth even if we know it or do not know it (The Truth remains the Truth)

*

Offline PmbPhy

  • Neilep Level Member
  • ******
  • 2788
    • View Profile
Quote from: Alan McDougall
"You know this Pete and your comment was uncalled for"!
This is supposed to be a friendly discussion and that's what I was posting into. Please don't make assertions such as "your comment was uncalled for" because it implies that I was intentionally being a perverse, because I most certainly wasn't (I know what I really meant).

Alan; I now consider you a friend and I never make rude comments to a friend of mine and I'm never sarcastic either. So I object to your (untrue) claim that I was reading into your statements something that is not there and then you claim that I know this which I most certainly didn't know. How do you know what I said was troublesome?

The statement you made that I commented on is this one - The answer to this question is much more complex than meets the eye?  When someone starts off a sentence with The answer to this question is ... which I understood, correctly or incorrectly[/i], to mean that you knew the answer. Just because a sentence ends with a question mark it doesn't mean that the person who wrote it was asking a question. There are uses of the question mark on sentences which are in reality statements and that's what I thought that you meant it to mean.

All you had to do was say that it wasn't what I made a mistake. After all I'm not the kind of person who can't admit that they made a mistake. So lets put this bed, okay?

*

Offline Alan McDougall

  • Neilep Level Member
  • ******
  • 1285
    • View Profile
Quote from: Alan McDougall
"You know this Pete and your comment was uncalled for"!
This is supposed to be a friendly discussion and that's what I was posting into. Please don't make assertions such as "your comment was uncalled for" because it implies that I was intentionally being a perverse, because I most certainly wasn't (I know what I really meant).

Alan; I now consider you a friend and I never make rude comments to a friend of mine and I'm never sarcastic either. So I object to your (untrue) claim that I was reading into your statements something that is not there and then you claim that I know this which I most certainly didn't know. How do you know what I said was troublesome?

The statement you made that I commented on is this one - The answer to this question is much more complex than meets the eye?  When someone starts off a sentence with The answer to this question is ... which I understood, correctly or incorrectly[/i], to mean that you knew the answer. Just because a sentence ends with a question mark it doesn't mean that the person who wrote it was asking a question. There are uses of the question mark on sentences which are in reality statements and that's what I thought that you meant it to mean.

All you had to do was say that it wasn't what I made a mistake. After all I'm not the kind of person who can't admit that they made a mistake. So lets put this bed, okay?

Noted Pete!! you are the last person I want as my enemy because I look up at you as an expert from which I can learn, as your insightful posts have proved many times.

If I can address the question posed in this thread.

We know that two objects like asteroids when they get close to each other, out there in space, will drift toward each other due to their mutual gravity fields, In that I do not see any bending of space, but a simple attraction due to mass and gravity.

Gravity this scenario looks more like a force such as magnetism although much, much weaker, but the effect it the same?

What is causing them to drift toward each other a force or the bending of space or both?
The Truth remains the Truth regardless of our beliefs or opinions the Truth is always the Truth even if we know it or do not know it (The Truth remains the Truth)

*

Offline IAMREALITY

  • Sr. Member
  • ****
  • 275
    • View Profile

What is causing them to drift toward each other a force or the bending of space or both?

Both.  The 'force' of gravity, which is a product of the the curvature of spacetime caused by any given mass.

*

Offline PhysBang

  • Hero Member
  • *****
  • 593
    • View Profile
What is causing them to drift toward each other a force or the bending of space or both?
One can describe spacetime in such a way that the objects, at rest, just approach each other with no force on the objects. This is part of general relativity.

*

Offline Alan McDougall

  • Neilep Level Member
  • ******
  • 1285
    • View Profile
What is causing them to drift toward each other a force or the bending of space or both?
One can describe spacetime in such a way that the objects, at rest, just approach each other with no force on the objects. This is part of general relativity.

Therefore Gravity is not a force?
« Last Edit: 01/07/2016 17:52:53 by Alan McDougall »
The Truth remains the Truth regardless of our beliefs or opinions the Truth is always the Truth even if we know it or do not know it (The Truth remains the Truth)

*

Offline JohnDuffield

  • Sr. Member
  • ****
  • 490
    • View Profile
It's not a force in the Newtonian sense, in that no work is done on a falling body. Gravity converts potential energy into kinetic energy, and when the latter is dissipated, you're left with a mass deficit. However if you look on the Einstein digital papers there's plenty of mentions of gravitational force, so IMHO one should be pedantic about this.

As for how gravity actually works, I think it's fairly straightforward. See this post where I attempted to explain it in easy-reading terms. 

*

Offline PhysBang

  • Hero Member
  • *****
  • 593
    • View Profile
However if you look on the Einstein digital papers there's plenty of mentions of gravitational force, so IMHO one should be pedantic about this.
It is not pedantic to answer the question. It is however, dishonest to present as a citation a search result that might appear to support the point that Einstein thought of gravity as a force when the specific search results do not support that conclusion.

The search results of Mr. Duffield's citation include the words of Einstein's translators, descriptions of the works of people other than Einstein, and Einstein speaking of other theories that General Relativity, including Newtonian mechanics. They do not include Einstein describing gravity in General Relativity.

Newtonian physics works extremely well for gravity, just not quite as well as General Relativity. Many people, including Einstein, will use Newtonian physics to set up a first approximation to a result and then use relativistic methods to finish a problem or application. This does not, however, commit them to the metaphysics of Newtonian physics. And the question of the OP is about the metaphysical content of gravitational theory. In General Relativity, gravity is not a force, it is part of the natural motion of particles.
Quote
As for how gravity actually works, I think it's fairly straightforward. See this post where I attempted to explain it in easy-reading terms.
Given the penchant of Mr. Duffield for providing, at the very least, misleading information about physics, I would recommend against following that link.

*

Offline Alan McDougall

  • Neilep Level Member
  • ******
  • 1285
    • View Profile
To simplify the question!

Are objects in space attracted towards each other due to their receptive masses bending the fabric of space?.

Or is gravity a force acting on objects causing them to drift towards each other if they get close enough something like magnetism?

Or is it both?

Is gravity a fundamental force of nature , like electromagnetism? the Graviton particle?

End of my comments (Alan)

http://www.qrg.northwestern.edu/projects/vss/docs/space-environment/1-what-is-gravity.html

What is gravity according to this article?

Gravity is a force pulling together all matter (which is anything you can physically touch). The more matter, the more gravity, so things that have a lot of matter such as planets and moons and stars pull more strongly.

Mass is how we measure the amount of matter in something. The more massive something is, the more of a gravitational pull it exerts. As we walk on the surface of the Earth, it pulls on us, and we pull back. But since the Earth is so much more massive than we are, the pull from us is not strong enough to move the Earth, while the pull from the Earth can make us fall flat on our faces.

In contrast Albert Einstein said

https://www.thestar.com/news/insight/2012/08/18/einstein_discovered_that_gravity_is_not_a_force_but_a_curvature.html

The classical theory of gravity had been a huge breakthrough in its time, and it still provides a good means of predicting the motion of objects. But it is wrong, in part because Newton misunderstood what gravity is.

Newton considered gravity to be a force that objects exert upon each other.

But, in a burst of brilliance, Einstein realized that no such force is required and in fact no such force exists.
« Last Edit: 02/07/2016 19:40:55 by Alan McDougall »
The Truth remains the Truth regardless of our beliefs or opinions the Truth is always the Truth even if we know it or do not know it (The Truth remains the Truth)

*

Offline JohnDuffield

  • Sr. Member
  • ****
  • 490
    • View Profile
It is not pedantic to answer the question. It is however, dishonest to present as a citation a search result that might appear to support the point that Einstein thought of gravity as a force...
It's not dishonest to refer to the Einstein digital papers. Einstein said what he said.

All: please take what PhysBang says with a pinch of salt. He's a stalker and a troll. He doesn't answer any of the questions, he just badmouths the people who do.

*

Offline PhysBang

  • Hero Member
  • *****
  • 593
    • View Profile
It is not pedantic to answer the question. It is however, dishonest to present as a citation a search result that might appear to support the point that Einstein thought of gravity as a force...
It's not dishonest to refer to the Einstein digital papers. Einstein said what he said.
It is dishonest to claim that there is a force of gravity because you can find it in a search of a set of documents. You clearly were trying to make an argument from authority to Einstein. It is important to counter your dishonesty by noting that the search results were not to the words of Einstein or were not about Einstein's own theory.
Quote
All: please take what PhysBang says with a pinch of salt. He's a stalker and a troll. He doesn't answer any of the questions, he just badmouths the people who do.
I also urge you to take everything I say with a pinch of salt. People on the internet are often dishonest. Mr. Duffield has given us a few examples of this.

*

Offline JohnDuffield

  • Sr. Member
  • ****
  • 490
    • View Profile
All: there's been no dishonesty from me. I stand by my references. Read them for yourself.

*

Offline puppypower

  • Hero Member
  • *****
  • 573
    • View Profile
If gravity was a force, there should be an exothermic output; release of energy potential, similar to the way the other three forces give off energy when they lower potential. Maybe dark energy is nothing more than the exothermic output from gravity. Neither the energy output from gravity or dark energy have been seen in the lab. However, both can be inferred from affect, apart from direct lab evidence.

For example, when the EM force lowers potential, the photons given off can cause the EM force to increase elsewhere, to create what appears to be an anti-EM force affect. When mass collapses due to gravity, a rotation will often appear. The rotation generates centrifugal force, which generates a force vector opposite gravity. This cause and affect is consistent with an opposing force being generated.

There are examples of spiral galaxies which more turns than should occur based on the age of the galaxy. This can be explained with the exothermic output profile due to gravity; winds from the center.   

*

Offline PhysBang

  • Hero Member
  • *****
  • 593
    • View Profile
What is causing them to drift toward each other a force or the bending of space or both?
One can describe spacetime in such a way that the objects, at rest, just approach each other with no force on the objects. This is part of general relativity.

Therefore Gravity is not a force?
If one accepts General Relativity, then gravity is not a force.

*

Offline PhysBang

  • Hero Member
  • *****
  • 593
    • View Profile
All: there's been no dishonesty from me. I stand by my references. Read them for yourself.
Mr. Duffield, I urge you of all people to read your own references. Please.

*

Offline AndroidNeox

  • Sr. Member
  • ****
  • 259
    • View Profile
Gravity curves spacetime because it stretches spacetime. A gravity well is "stretched", or "dilated", spacetime. Matter exists within spacetime. Light travels through spacetime. Some property of mass causes spacetime to stretch. I think the coupling between mass (or energy, because E=mc˛ has something to do with the Higgs field, but I don't understand Higgs).

The commonly used rubber sheet model is very good in that it shows the stretching as well as, conveniently, letting one roll a marble around the simulated gravity well, simulating an object in orbit. The amount of spacetime dilation is proportional to the difference in gravitational potential energy between two points. The delay in the travel time of a beam of light traveling through a gravity well due to the increase in path because space is stretched is called the Shapiro Delay. For example, between the Earth and the Sun, space is stretched about 60 km, due to the difference in gravitational potential energy.

Ideally, the rubber sheet can stretch infinitely, is perfectly slippery, and stretches vertically with an ideal spring constant (the depth of the well is directly proportional to the mass in the middle). If the mass is fluid, e.g. mercury or BBs, then the sheet will follow a correct curve even under the surface of the fluid mass, curving more toward horizontal instead of getting progressively steeper. The maximum spacetime stretch will be at the center point, when the sheet is stretched deepest. Note, in the center of gravity of an object, although spacetime is maximally dilated and time goes slowest, there is no net gravitational vector so the observer, there,  wouldn't feel any gravity, they'll be in freefall, but their clock will run slower than for an observer at higher gravitational potential energy.

The rubber sheet model is also excellent because the stretch to space is entirely radial about the mass. For example, if the sun were compressed to a black hole, the orbital circumference of the Earth would remain unchanged but the measurable distance to the center of our orbit would approach infinite. The Shapiro delay to any event horizon will be infinite.

But, don't get hung up on the idea that spacetime is a thing. It's just an imaginary framework we've established for showing how motion in different frames relate to each other. Each observer has a "local" stationary, the local inertial frame. Whether you are experiencing acceleration or not, you can define an inertial frame. For example, for an observer in 1 g of acceleration, an inertial frame would fall downward at ~32 ft/sec/sec. For an astronaut floating freely in free fall, she is occupying her inertial frame, whether they are far from any masses or in vacuum in orbit around a planet.
« Last Edit: 15/07/2016 02:22:47 by AndroidNeox »

*

Offline PmbPhy

  • Neilep Level Member
  • ******
  • 2788
    • View Profile
Alan - The curvature of spacetime is just another name for tidal gradients. That's all that it is. The curvature of space refers to the fact that if you take measurements of spatial distances between points in space then you'd find that they don't behave like that measurements you'd expect from taking measurements between points in flat space. The distances change and they have the properties of a curved space.

There's nothing wrong with referring to gravity as a force. Einstein did. What Einstein meant was that the force of gravity is an inertial force. Before Einstein inertial forces, like the Coriolis force and centrifugal forces, were thought of as fictitious, i.e. being due to the wrong choice of a frame of reference. Einstein argued that since the gravitational force behaves like an inertial force and since he considered the gravitational force as being "real" he asserted that inertial forces are also "real."  You can read what Einstein and other contemporary physicists wrote on this point at my website at: http://www.newenglandphysics.org/physics_world/gr/inertial_force.htm

Here is the derivation for the expression for the inertial force in general relativity:
http://www.newenglandphysics.org/physics_world/gr/grav_force.htm

*

Offline Alan McDougall

  • Neilep Level Member
  • ******
  • 1285
    • View Profile
Alan - The curvature of spacetime is just another name for tidal gradients. That's all that it is. The curvature of space refers to the fact that if you take measurements of spatial distances between points in space then you'd find that they don't behave like that measurements you'd expect from taking measurements between points in flat space. The distances change and they have the properties of a curved space.

There's nothing wrong with referring to gravity as a force. Einstein did. What Einstein meant was that the force of gravity is an inertial force. Before Einstein inertial forces, like the Coriolis force and centrifugal forces, were thought of as fictitious, i.e. being due to the wrong choice of a frame of reference. Einstein argued that since the gravitational force behaves like an inertial force and since he considered the gravitational force as being "real" he asserted that inertial forces are also "real."  You can read what Einstein and other contemporary physicists wrote on this point at my website at: http://www.newenglandphysics.org/physics_world/gr/inertial_force.htm

Here is the derivation for the expression for the inertial force in general relativity:
http://www.newenglandphysics.org/physics_world/gr/grav_force.htm

Thank you, Pete, I went to both links ,the maths  a bit hard for me to follow?

Here, however , is an excerpt from one of the links

'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''

Here is the derivation for the expression for the inertial force in general relativity:

http://www.newenglandphysics.org/physics_world/gr/grav_force.htm


I could not copy and paste the equations

In what follows it must be kept in mind that “no G’s mean no gravitational force.” This should not be confused with ”G means gravitational force”. The former is always true while the later may or may not be true.

In general relativity, gravitational effects manifest themselves through the metric tensor gmn. According to Einstein's Equivalence Principle an accelerating frame of reference is locally equivalent to a gravitational field.

This means that in the absence of a 4-force on particle, the only force acting on the particle will be equivalent to an inertial force, the force resulting entirely from observing the particles motion from a frame of reference accelerating with respect to an inertial frame. Since the first term on the right side of Eq. (4) is proportional to the 4-force it follows that the second term on the right side of Eq. (4) represents the gravitational force.

"If I understand it correct the word "Force" is not a "No-No", when describing gravity?

Alan



The Truth remains the Truth regardless of our beliefs or opinions the Truth is always the Truth even if we know it or do not know it (The Truth remains the Truth)

*

Offline PmbPhy

  • Neilep Level Member
  • ******
  • 2788
    • View Profile
Quote from: Alan McDougall
Thank you, Pete, I went to both links ,the maths  a bit hard for me to follow?
It's not important to be able to follow the derivation. All that you need to know is the result which is Eq. (8a) and the fact that the value for the gravitational force equals the time rate of change of momentum of a particle in a gravitational field. Notice the value of it, i.e.

Gk = m(components of the gravitational field)x(velocity terms)

Here m is the relativistic mass of the particle. Notice how this compares with the Lorentz force, Eq (9) (the force on a charged particle in an electromagnetic field) in that its charge x field x velocity terms. That's why I like relativistic mass, i.e. its like a gravitational charge.

Quote from: Alan McDougall
Here, however , is an excerpt from one of the links
....
I could not copy and paste the equations
That's because the only way I knew of, at least the easiest way, was to write the page in MS Word using its equation editor, the do a screen capture and the use that image of the equation in the webpage. So its actually a GIF file, not something you can cut and past.

Quote from: Alan McDougall
"If I understand it correct the word "Force" is not a "No-No", when describing gravity?
That's a matter of opinion. I know of several GR experts who think of it as a force. I actually showed you a page of quotations from some physicists on this. Just keep in mind that the gravitational force in GR is an inertial force. Now recall the page I posted before, i.e.
http://www.newenglandphysics.org/physics_world/gr/inertial_force.htm

Take a look at it again. Read this quote
Quote
From Introducing Einstein's Relativity, by Ray D'Inverno, Oxord/Clarendon Press, (1992) page 122   

Notice that all inertial forces have the mass as a constant of proportionality in them. The status of inertial forces is again a controversial one. One school of thought describes them as apparent or fictitious which arise in non-inertial frames of reference (and which can be eliminated mathematically by putting the terms back on the right hand side). We shall adopt the attitude that if you judge them by their effects then they are very real forces.
Here the author is saying that the gravitational force is a real force.

Now read the quote from Einstein.

*

Offline PmbPhy

  • Neilep Level Member
  • ******
  • 2788
    • View Profile
A good example of how the gravitational force is mentioned in general relativity textbooks can be seen by downloading the following text, which is quite well known and whose author was a renown expert in general relativity

Theory of Relativity (International Series of Monographs on Physics) by C. Moller
http://book4you.org/book/860357/c15966

You'll have to first register for the site and then download and install a STDU reader. In this text you'll find that the author provides a derivation for the gravitational force too. His seems to be the same. I didn't follow a text to get my result but mine is the same as his as, of course, it must be.

Using the STDU reader do a search in this text on the term gravitational force and you'll get a list of all the instances where Moller uses it. If you'd like I can teach you general relativity in the NEP forum. It's not as difficult as you might think. Trust me. :)

*

Offline PhysBang

  • Hero Member
  • *****
  • 593
    • View Profile
Einstein argued that since the gravitational force behaves like an inertial force and since he considered the gravitational force as being "real" he asserted that inertial forces are also "real."  You can read what Einstein and other contemporary physicists wrote on this point at my website at: http://www.newenglandphysics.org/physics_world/gr/inertial_force.htm
That Einstein used dubious metaphysics is not an argument for adopting dubious metaphysics.

*

Offline Jack Qwek

  • Jr. Member
  • **
  • 13
    • View Profile
To me is both things. When you drop a stone in the water, are the waves caused by the stone, or are the waves circular because of the stone? It's both, the waves are caused by the stone and their shape is circular. In the same way, gravity attracts and bend everything, including light. But space itself is not straight nor bent, space has no shape at all. But these things are so obvious that there is no need to quote Einstein, even Newton was aware of this.

*

Offline Alan McDougall

  • Neilep Level Member
  • ******
  • 1285
    • View Profile
To me is both things. When you drop a stone in the water, are the waves caused by the stone, or are the waves circular because of the stone? It's both, the waves are caused by the stone and their shape is circular. In the same way, gravity attracts and bend everything, including light. But space itself is not straight nor bent, space has no shape at all. But these things are so obvious that there is no need to quote Einstein, even Newton was aware of this.

A warm welcome to the forum if you have not already been welcomed by some other member!

Space is said to be like a fabric that can bend twist and contort, under the influence of gravity.
The Truth remains the Truth regardless of our beliefs or opinions the Truth is always the Truth even if we know it or do not know it (The Truth remains the Truth)

*

Offline PhysBang

  • Hero Member
  • *****
  • 593
    • View Profile
But space itself is not straight nor bent, space has no shape at all. But these things are so obvious that there is no need to quote Einstein, even Newton was aware of this.
Sadly, what is obvious to one person is not to others. There is a lot of literature on the shape of space and applications that rely on this knowledge.

*

Offline IAMREALITY

  • Sr. Member
  • ****
  • 275
    • View Profile
To me is both things. When you drop a stone in the water, are the waves caused by the stone, or are the waves circular because of the stone? It's both, the waves are caused by the stone and their shape is circular. In the same way, gravity attracts and bend everything, including light. But space itself is not straight nor bent, space has no shape at all. But these things are so obvious that there is no need to quote Einstein, even Newton was aware of this.

A warm welcome to the forum if you have not already been welcomed by some other member!

Space is said to be like a fabric that can bend twist and contort, under the influence of gravity.

Actually I believe the preferred position nowadays of most versed physicists is to not think of spacetime like a fabric at all, and they wince at it being portrayed as such.  But I might be wrong.

*

Offline PmbPhy

  • Neilep Level Member
  • ******
  • 2788
    • View Profile
Quote from: PhysBang
That Einstein used dubious metaphysics is not an argument for adopting dubious metaphysics.
And where,  pray tell, in this forum did I make such an argument? All I said is that there are physicists, including Einstein, who though of it that way. And it's far from being dubious in any way, shape of form whatsoever. And this isn't dubious anyway. Just because that's your opinion it doesn't mean that it reflects anybody else's opinion. Far from it in fact.

In any case what Einstein thought on points like this should never be dismissed or ignored. It was those kinds of thoughts which helped lead him to his general theory of relativity. Why do you think Einstein is quoted so often such as in articles which try to convince physicists to stop teaching relativistic mass. In nearly all of those articles they quote his statement against velocity dependent mass. However, little did they know he wasn't speaking of relativistic mass in general.

Next time (or at least until the ignore list function is working again) please make an effort for present a cogent argument of your beliefs rather than merely stating assertions such as "dubious metaphysics". Merely making assertions by stating your opinion helps nobody.
« Last Edit: 15/07/2016 16:42:34 by PmbPhy »