Story Wednesday October 19, 2016

[Don Edwards 548]

1 hour ago, hkmaly said:

As I read it, in special theory of relativity, acceleration makes your frame of reference "worse" (non-inertial). In general theory of relativity, so can gravitation. Both are present on Earth.

But a thing can't just accelerate. It has to accelerate its motion relative to something else. And it's equally valid to say that the something else is accelerating its motion relative to the thing.

[hkmaly 490]

11 minutes ago, Don Edwards said:

1 hour ago, hkmaly said:

As I read it, in special theory of relativity, acceleration makes your frame of reference "worse" (non-inertial). In general theory of relativity, so can gravitation. Both are present on Earth.

But a thing can't just accelerate. It has to accelerate its motion relative to something else. And it's equally valid to say that the something else is accelerating its motion relative to the thing.

Yes it can. Under special theory of relativity, you can recognize that you are accelerating by measuring the force affecting you. In non-intertial frames of reference, there are nonzero fictitious forces affecting you. You don't need to SEE any other frame of reference to recognize that there must be some where the fictitious ARE zero. (Note that it's VECTOR zero, meaning vector with zero length ; negative numbers can appear there in sane spaces.)

Under general theory of relativity, the gravitation is indistinguishable from such fictitious force, but that doesn't matter, as both gravitation and fictitious forces would confirm you are NOT in inertial frame of reference. Again, only if you measure zero force, you are in inertial frame of reference.

(Read the wikipedia, or better, an actual physic book.)

[ijuin 572]

Two frames of reference don't both have to be inertial to be equivalent. Rather, they are equivalent if their accelerations are equal--the acceleration can be any value. For example, the interior of an enclosed capsule accelerating in free space directly away from the center of Earth at 9.8 m/s^2 is equivalent to the interior of an identical capsule sitting on Earth's surface feeling 9.8 m/s^2 of gravitational acceleration.

[hkmaly 490]

15 hours ago, ijuin said:

Two frames of reference don't both have to be inertial to be equivalent. Rather, they are equivalent if their accelerations are equal--the acceleration can be any value. For example, the interior of an enclosed capsule accelerating in free space directly away from the center of Earth at 9.8 m/s^2 is equivalent to the interior of an identical capsule sitting on Earth's surface feeling 9.8 m/s^2 of gravitational acceleration.

Sure. But not only inertial and non-inertial frames of references are not equivalent, but it also can be said that inertial frame of reference is "better" than non-inertial - in the "more special" sense. Therefore, non-inertial frame of reference makes bad "centre of universe".

(Note that technically, the acceleration can be any vector, not value. Direction matters.)

[Don Edwards 548]

Ah, so there IS a preferred frame of reference... distinguished by, among other things, the fact that it does not exist anywhere in the universe.

[hkmaly 490]

On 10/22/2016 at 6:45 AM, Don Edwards said:

Ah, so there IS a preferred frame of reference... distinguished by, among other things, the fact that it does not exist anywhere in the universe.

Not a SINGLE one, mind you. Lot of them. And, yeah, technically, you are ALWAYS in some gravitation field, or at least until we manage to develop quantum theory of gravitation and prove that the gravitation somewhere in middle of nothing between galaxy clusters is lower than one quantum of it so effectively zero ...

[ijuin 572]

On the other hand, we don't need it to be zero to calculate accurately to at least eight or nine significant figures--GPS satellites for example, are accurate in the part-per-billion range because we can calculate how much the time and space dilation from Earth, Moon, and Sun affect the radio signal and onboard clocks.

[hkmaly 490]

1 hour ago, ijuin said:

On the other hand, we don't need it to be zero to calculate accurately to at least eight or nine significant figures--GPS satellites for example, are accurate in the part-per-billion range because we can calculate how much the time and space dilation from Earth, Moon, and Sun affect the radio signal and onboard clocks.

That's true but I'm not sure how it's related to discussion.

[ijuin 572]

Oh, just that frames of reference don't have to be perfectly equivalent--there is such a thing as "close enough", even in quantum mechanics.

[hkmaly 490]

4 hours ago, ijuin said:

Oh, just that frames of reference don't have to be perfectly equivalent--there is such a thing as "close enough", even in quantum mechanics.

"close enough" is actually especially true IN quantum mechanics, because anything closer than 1.6 x 10^-35 m is at same place. Except all attempts of quantum theory of gravitation or any other way how to combine general theory of relativity with quantum physic failed.

We are only able to compute GPS because we DONT take quantum physics into account. Luckily, everything is big enough so we can afford to do that.