More Special Relativity Questions... (1 Viewer)

[jskeza]

These may be dumb questions because I haven't gotten the basics of Special Relativity down yet...

1. How do GPS satellites experience special relativity if they are in an accelerating frame of reference (caused by its centripetal acceleration)? I thought special relativity only applied to objects in inertial frames of reference (i.e. frames of references that don't accelerate).

Also another question that I've seen somewhere...
2. What happens if a terminally ill person is put into space at near speed of light? Since time on Earth goes faster than on the spaceship they could return after a cure is found. Would this work? Why or why not?

Thanks!

 

[Drdusk]

1. Correct. Special relativity only applies to objects in inertial frames of reference. You are also correct in saying that the satellites would have an acceleration and so special relativity would not apply.

However Einstein invented two different types of relativity, Special and General. The General theory of relativity is MUCH MUCH harder and it deals with scenarios such as this when you would have an acceleration, such as a satellite in orbit. Now really for such small velocities, really it does not matter at the HSC level if you say Special relativity, but you should be mentioning that it does have an acceleration.

2.
Yes it would work. If they're on a spaceship, time flows slower for them. So for example a year for that patient might be like 10 years on Earth. This means when they come back to Earth, they have not moved as far forward in time as people on the Earth would have.


Just so you know how much harder General relativity is. It took Einstein 1 year to develop Special relativity, and 10 years to develop General relativity

 

[jskeza]

1. Correct. Special relativity only applies to objects in inertial frames of reference. You are also correct in saying that the satellites would have an acceleration and so special relativity would not apply.

However Einstein invented two different types of relativity, Special and General. The General theory of relativity is MUCH MUCH harder and it deals with scenarios such as this when you would have an acceleration, such as a satellite in orbit. Now really for such small velocities, really it does not matter at the HSC level if you say Special relativity, but you should be mentioning that it does have an acceleration.

2.
Yes it would work. If they're on a spaceship, time flows slower for them. So for example a year for that patient might be like 10 years on Earth. This means when they come back to Earth, they have not moved as far forward in time as people on the Earth would have.


Just so you know how much harder General relativity is. It took Einstein 1 year to develop Special relativity, and 10 years to develop General relativity

Thanks for the quick reply!

 

[blyatman]

Again another thing that's taught incorrectly in high school.

You do NOT need general relativity for accelerating frames. Special relativity can very easily handle accelerating frames of reference, but it requires calculus so it's not taught in HS physics. SR assumes that you're in a vaccum, away from any masses/gravitational fields. This was the motivation for GR, which is a more complete theory that accounts for gravitational fields. SR is for flat spacetime (where there is no gravity) and GR is for curved spacetime. You recover the SR equations if you simply set M = 0 in the GR equations.

For satellites in orbit, there are two types of time dilation: Kinematic (due to its speed, which can be tackled by SR) and gravitational (due to its position in a gravitational field, which is tackled by GR). Both types of time dilation occur and have to be accounted for. Look up the Hafele-Keating experiment on wiki for more details if interested.

They really need to revamp the entire HSC relativity section lol. The aether, mass dilation, SR not handling acceleration, it's all a bunch of nonsense.

 

[jskeza]

Again another thing that's taught incorrectly in high school.

You do NOT need general relativity for accelerating frames. Special relativity can very easily handle accelerating frames of reference, but it requires calculus so it's not taught in HS physics. SR assumes that you're in a vaccum, away from any masses/gravitational fields. This was the motivation for GR, which is a more complete theory that accounts for gravitational fields. SR is for flat spacetime (where there is no gravity) and GR is for curved spacetime. You recover the SR equations if you simply set M = 0 in the GR equations.

For satellites in orbit, there are two types of time dilation: Kinematic (due to its speed, which can be tackled by SR) and gravitational (due to its position in a gravitational field, which is tackled by GR). Both types of time dilation occur and have to be accounted for. Look up the Hafele-Keating experiment on wiki for more details if interested.

They really need to revamp the entire HSC relativity section lol. The aether, mass dilation, SR not handling acceleration, it's all a bunch of nonsense.

Thanks for the help, it is an interesting topic so far. I watched a few videos saying mass doesn't increase as you approach c, but HSC physics says it does...

 

[blyatman]

Thanks for the help, it is an interesting topic so far. I watched a few videos saying mass doesn't increase as you approach c, but HSC physics says it does...

Yeh I'm not sure why the HSC is still pushing that narrative. It's widely accepted in the scientific community that mass stays constant, but rather it's the energy of the body that goes to infinity. Nonetheless, you need to spit out what they want in the exam.

 

[Drdusk]

Again another thing that's taught incorrectly in high school.

You do NOT need general relativity for accelerating frames. Special relativity can very easily handle accelerating frames of reference, but it requires calculus so it's not taught in HS physics.

Ummmmmmm, oook I should just drop out already.........

Well obviously take Blyatman's word over mine, but as far as HSC Physics goes, it's alright to stick with what I said

 

[blyatman]

Ummmmmmm, oook I should just drop out already.........

Lol, nah keep going, and if you end up going into physics education, change the system from within.

 

[blyatman]

Thanks for the help, it is an interesting topic so far. I watched a few videos saying mass doesn't increase as you approach c, but HSC physics says it does...

If you're interested, I'd highly recommend watching these (the first one in particular):

It explains very clearly why relativity is fundamentally needed (note how the word aether is not even mentioned). In HS, they teach SR as a theory that improves upon Newtonian mechanics by assuming the constancy of the speed of light, which couldn't be further from the truth. Einstein's SR paper was not called "On the constancy of the speed of light", it was called "On the electrodynamics of moving bodies". Relativity is not a mechanics theory, it is fundamentally an electrodynamic theory.

It's such a shame that the historical/scientific context and necessity of relativity is not taught properly. It is crucial to properly understand it, and it really helps you appreciate why relativity, the most beautifully intricate scientific theory, is universally considered as humanity's greatest intellectual achievement.

 

[jskeza]

I'll have to check these videos out, they seem very interesting!