radial centered acceleration

[michel123456]

It has been said that if an observer is in a state of acceleration, he can use physics to know it & determine the acceleration.

For example, if you were born on a spaceship going to a distant star, and if this spaceship is accelerating say 1g, the young astronaut, after reading books of physics, can make experiments that will tell him that he is in a state of acceleration. He will also be capable to determine the direction of acceleration.

Say that the astronaut is indeed measuring that he is accelerated. The value is 1g. He immediately understands that he is traveling aboard a spaceship, accelerating.

Now the strange thing is that the direction of the acceleration is not towards a distant star. No, things are not that simple.

The direction of the acceleration is radial: it goes from the outside to the inside. As a result, the astronaut infers that this radial acceleration is not caused by any kind of motion through space (how could that be?) The astronaut decides that this acceleration is caused by another phenomena: mass.

...

We are the astronauts.

Why don't we focus back on the original question :how could that be?

Is it impossible to describe a situation where the geometry of space is changing under acceleration? A situation in which the observer would be able to measure a radial centered acceleration?

[Strange]

1 hour ago, michel123456 said:

For example, if you were born on a spaceship going to a distant star, and if this spaceship is accelerating say 1g, the young astronaut, after reading books of physics, can make experiments that will tell him that he is in a state of acceleration. He will also be capable to determine the direction of acceleration.

This doesn't take much. A plumb line to tell the direction. A spring balance to measure the magnitude.

Of course, unless the spaceship has windows, he wouldn't be able to tell if he was accelerating or still sat on the launchpad!

1 hour ago, michel123456 said:

Now the strange thing is that the direction of the acceleration is not towards a distant star.

I don't understand this. If the spaceship is heading directly towards the star, then why wouldn't that be the direction of acceleration? (Apart from the fact that the star is moving, so the spaceship might be aiming ahead of it to where it will be on arrival)

1 hour ago, michel123456 said:

Is it impossible to describe a situation where the geometry of space is changing under acceleration? A situation in which the observer would be able to measure a radial centered acceleration?

That is exactly what we measure when standing stationary on the surface of the Earth.

But I'm not sure I understand the question ...

[swansont]

1 hour ago, michel123456 said:

 Why don't we focus back on the original question :how could that be?

Is it impossible to describe a situation where the geometry of space is changing under acceleration? A situation in which the observer would be able to measure a radial centered acceleration?

You have already noted that one can make this measurement.

Do you mean measure a radial acceleration, distinct from gravity? Tell them apart?

[Lasse]

6 hours ago, michel123456 said:

It has been said that if an observer is in a state of acceleration, he can use physics to know it & determine the acceleration.

For example, if you were born on a spaceship going to a distant star, and if this spaceship is accelerating say 1g, the young astronaut, after reading books of physics, can make experiments that will tell him that he is in a state of acceleration. He will also be capable to determine the direction of acceleration.

Say that the astronaut is indeed measuring that he is accelerated. The value is 1g. He immediately understands that he is traveling aboard a spaceship, accelerating.

Now the strange thing is that the direction of the acceleration is not towards a distant star. No, things are not that simple.

The direction of the acceleration is radial: it goes from the outside to the inside. As a result, the astronaut infers that this radial acceleration is not caused by any kind of motion through space (how could that be?) The astronaut decides that this acceleration is caused by another phenomena: mass.

...

We are the astronauts.

Why don't we focus back on the original question :how could that be?

Is it impossible to describe a situation where the geometry of space is changing under acceleration? A situation in which the observer would be able to measure a radial centered acceleration?

Which geometry space can have if it has velocity?

Can space has velocity (speed/rate) with which it is expanding? 

Does its perception and presentation is related to the physical circumstances(energy/mass) in which the observation occure?

Can we confidentally say space is absolutely static?

If space has velocity can it be impacted by mass? How?

Space is volume. Basic 4D information. Time can not be sepatered from it.

Could you give me a handful of it (space or time)? Can I say that they are still part on Nature and by that they seems to be physical?

If the Laws of Nature can be true Universally isn't it applied through space and time or space is just a consequence?

Can space itself has acceleration or can it have firm velocity  (with applied limit measurable by Time) or Does space is absolutely static?

 

If space could have velocity would that mean that it has a center or space is absolutely amorphous?

Is it possible to count space(time) as an observer i.e. from its point of view we observe?

Edited April 6, 2018 by Lasse

[Strange]

1 hour ago, Lasse said:

Which geometry space can have if it has velocity?

Can space has velocity (speed/rate) with which it is expanding? 

You would be better off starting a thread to ask your questions.

Space is not a "thing" and cannot have a speed. Expansion is a scaling of the distances between points in space, not a speed. The relative speed of objects in expanding space is proportional to how far apart they are.

1 hour ago, Lasse said:

Does its perception and presentation is related to the physical circumstances(energy/mass) in which the observation occure?

Yes, the geometry of space is affected by the presence of mass and energy.

1 hour ago, Lasse said:

Can we confidentally say space is absolutely static?

Absolutely not.

[michel123456]

7 hours ago, Strange said:

That is exactly what we measure when standing stationary on the surface of the Earth.

But I'm not sure I understand the question ...

Yes that is exactly what we measure when standing stationary on the surface of the Earth.

Gravity is the question.

 

6 hours ago, swansont said:

You have already noted that one can make this measurement.

Do you mean measure a radial acceleration, distinct from gravity? Tell them apart?

Why tell them apart? We know they are indistinctible.

Simply don't give it a name, don't call it gravity. Try to explain this acceleration by other means. Keep it as a custom acceleration, a kind of motion. Maybe explaining  it through some subtle transformation of the geometry.

Edited April 6, 2018 by michel123456

[Strange]

9 minutes ago, michel123456 said:

Try to explain this acceleration by other means. Keep it as a custom acceleration, a kind of motion. Maybe explaining  it through some subtle transformation of the geometry.

I’m afraid Prof Einstein beat you to that insight!

If you want to interpret it as motion, then this coordinate system is what you need: https://en.m.wikipedia.org/wiki/Gullstrand–Painlevé_coordinates

[michel123456]

21 minutes ago, Strange said:

I’m afraid Prof Einstein beat you to that insight!

If you want to interpret it as motion, then this coordinate system is what you need: https://en.m.wikipedia.org/wiki/Gullstrand–Painlevé_coordinates

Einstein has proposed to explain gravity by the bending of spacetime, yes. But his explanation consists of saying that mass bends spacetime (as a weight placed on a membrane). Here is the opposite: the radial accelerated motion creates the effect of gravity. As if a "universal motion" was applied to all "objects", giving them gravity. Something like an explosion. Or better: a scale factor. But with acceleration.

And yes, the GP coordinates describe such kind of situation, where the geometry dictates the behavior. Not in this way though.

[Strange]

1 hour ago, michel123456 said:

Einstein has proposed to explain gravity by the bending of spacetime, yes. But his explanation consists of saying that mass bends spacetime (as a weight placed on a membrane). Here is the opposite: the radial accelerated motion creates the effect of gravity.

That is exactly the same thing. In GR, standing on the surface of the earth is to experience continuous radial acceleration.

1 hour ago, michel123456 said:

Not in this way though.

Can you clarify what you think is different?

[swansont]

3 hours ago, michel123456 said:

Why tell them apart? We know they are indistinctible.

Simply don't give it a name, don't call it gravity. Try to explain this acceleration by other means. Keep it as a custom acceleration, a kind of motion. Maybe explaining  it through some subtle transformation of the geometry.

If you can do better than relativity, go for it.

[michel123456]

10 hours ago, Strange said:

 

Can you clarify what you think is different?

If I understand clearly, the GP coordinates correspond to a raindrop on a Black Hole. The concept would be to extend this to all cases, not necessarily to a BH.

Also:

The statement: " Define a raindrop as an object which plunges radially toward a black hole from rest at infinity" does not correspond. There is no "rest at infinity", there is a never ending continuous process, always the same as seen by the raindrop. Something like a plunging orbit in a fractal. All masses would be raindrops.

[swansont]

"At rest from infinity" is a statement about how much energy it has, not about a process.