Why don't stars change position?

@Metal-Brain
Try looking up the word 'equivalence'

@sonhouse said
@Metal-Brain
Try looking up the word 'equivalence'

Right, there is not an absolute equivalence. That is why you must ask yourself why the equivalence principal is constantly brought up when discussing GR. It is because that is the thought experiment that led Einstein to realize that if speed causes time dilation and velocity could simulate gravity, that time dilation could be the cause of gravity as well.

That has to be the case, otherwise why compare velocity with speed? They are not the same thing and Einstein knew that. If gravity caused time dilation the equivalence principal would be 100% irrelevant.

@Metal-Brain
Since you are SO much smarter than anyone here, tell us oh mighty one what causes time 'dilation'.

@sonhouse said
@Metal-Brain
Since you are SO much smarter than anyone here, tell us oh mighty one what causes time 'dilation'.

MASS

@Metal-Brain
Well then, that means 'time dilation' does not cause gravity, MASS causes BOTH time flow changes and what we perceive as gravity.

@metal-brain said
Right, there is not an absolute equivalence. That is why you must ask yourself why the equivalence principal is constantly brought up when discussing GR. It is because that is the thought experiment that led Einstein to realize that if speed causes time dilation and velocity could simulate gravity, that time dilation could be the cause of gravity as well.

That has to b ...[text shortened]... stein knew that. If gravity caused time dilation the equivalence principal would be 100% irrelevant.

You're saying "velocity" sometimes where you should be saying "acceleration." On purpose?

Speed is a scalar quantity that by definition is the magnitude of a velocity vector.

@soothfast said
You're saying "velocity" sometimes where you should be saying "acceleration." On purpose?

Speed is a scalar quantity that by definition is the magnitude of a velocity vector.

That was an accident. I meant acceleration.

It is not a true equivalence. "velocity" is not "acceleration". It was the thought experiment that made Einstein realize that time dilation causes gravity. People that claim gravity causes time dilation don't know what they are talking about. Just ask them why gravity causes time dilation. They never have an answer because they have it backwards and are in denial of it.

@sonhouse said
@Metal-Brain
Well then, that means 'time dilation' does not cause gravity, MASS causes BOTH time flow changes and what we perceive as gravity.

As I have told you countless times before I am using the term "cause" loosely and that "is" would be more accurate, but to say gravity causes time dilation is retarded. Time dilation is gravity. Objects are attracted to where time passes slower. That is what Brian Greene meant when he said "objects do not like to age".

It is obvious that Brian Greene is saying time dilation is gravity. Only a person bent on remaining in denial would claim otherwise.

@metal-brain said
As I have told you countless times before I am using the term "cause" loosely and that "is" would be more accurate, but to say gravity causes time dilation is retarded. Time dilation is gravity. Objects are attracted to where time passes slower. That is what Brian Greene meant when he said "objects do not like to age".

It is obvious that Brian Greene is saying time dilation is gravity. Only a person bent on remaining in denial would claim otherwise.

General relativity is a way of interpreting gravity as a manifestation of the geometry of spacetime, with the geometry being determined by the distribution of mass. Some go so far as to say this means gravity is not really a force, but I don't quite agree with that. I mean, we have to ask why mass influences the geometry of spacetime in its vicinity. What's mediates the influence? Gravitons, perhaps? There isn't a firm answer.

One could turn things around, I think, and instead say mass has "heft" precisely because mass is a manifestation of the geometry of spacetime. That is, mass is a manifestation of the shape of spacetime, rather than mass giving spacetime its shape. Mathematically I believe the two interpretations are equivalent. Physicists commonly have different interpretations of a physical phenomenon that are mathematically equivalent (i.e. as models of reality they fit the known facts and make the same predictions).

@metal-brain said

It is obvious that Brian Greene is saying time dilation is gravity. Only a person bent on remaining in denial would claim otherwise.

I think this has something to do with an interpretation of physical motion that holds that the reason an object falls toward a mass (such as a planet) is because it is merely moving along the equivalent of a straight line (i.e. a geodesic) in the four-dimensional spacetime continuum. Mathematically consistent with this view is the idea that time slows in the vicinity of a mass.

@soothfast said
I think this has something to do with an interpretation of physical motion that holds that the reason an object falls toward a mass (such as a planet) is because it is merely moving along the equivalent of a straight line (i.e. a geodesic) in the four-dimensional spacetime continuum. Mathematically consistent with this view is the idea that time slows in the vicinity of a mass.

So you agree Brian Greene is saying time dilation is gravity. Good to know.

@soothfast said
General relativity is a way of interpreting gravity as a manifestation of the geometry of spacetime, with the geometry being determined by the distribution of mass. Some go so far as to say this means gravity is not really a force, but I don't quite agree with that. I mean, we have to ask why mass influences the geometry of spacetime in its vicinity. What's mediat ...[text shortened]... cally equivalent (i.e. as models of reality they fit the known facts and make the same predictions).

The manifestation of the geometry of spacetime is time dilation. Time dilation causes the bending of spacetime. Spacetime cannot bend without time dilation. If it could it would just be called space, not spacetime. Space and time are inextricably linked. You cannot have one without the other.

@metal-brain said
So you agree Brian Greene is saying time dilation is gravity. Good to know.

I don't know what Brian Greene says, but I don't agree with that idea. Time dilation also occurs merely by moving (from the point of view of one who is not). It's what's needed in order for the speed of light to be a constant from all points of view: fast, slow, accelerating, not accelerating. This is codified in special relativity, as opposed to general relativity. Special relativity doesn't deal with gravity as it is usually defined in physics textbooks.

@Soothfast
I see your profile says you live in Pa, just wondered what part? I reside in the Pocono Mountains north of Philly about 80 miles.

@sonhouse said
@Soothfast
I see your profile says you live in Pa, just wondered what part? I reside in the Pocono Mountains north of Philly about 80 miles.

Montgomery County area. Maybe an hour away from you.