Why is Galileo's Principle of Relativity always true? (3 Viewers)

[Trial&Error]

I've been wondering this about The Theory of Special Relativity:

In Einstein's thought experiment below, he comes to the conclusion "YES" because Galileo's PoR cannot be violated. But why is that? Special Relativity mainly resides on the fact that Galileo's principle is always true, but what evidence is there?

"If a person is sitting in a train travelling at speed "c", and holds up a mirror, will they be able to see their reflection?"

Yes: This would satisfy Galileo's PoR, but from a stationary observers pov, c+c=2c, which is not true. This led to concluding that light is an absolute constant and time and distance are relative.

No: The light will not reach the mirror in order to be reflected back, but then the person will know from their inertial frame of reference that they are travelling at speed "c", violating Galileo's PoR.

Thanks.

 

[coolcat6778]

this is just rote learning lol, i genuinely don't think the markers look for actual knowledge in responses

 

[dumNerd]

I've been wondering this about The Theory of Special Relativity:

In Einstein's thought experiment below, he comes to the conclusion "YES" because Galileo's PoR cannot be violated. But why is that? Special Relativity mainly resides on the fact that Galileo's principle is always true, but what evidence is there?

"If a person is sitting in a train travelling at speed "c", and holds up a mirror, will they be able to see their reflection?"

Yes: This would satisfy Galileo's PoR, but from a stationary observers pov, c+c=2c, which is not true. This led to concluding that light is an absolute constant and time and distance are relative.

No: The light will not reach the mirror in order to be reflected back, but then the person will know from their inertial frame of reference that they are travelling at speed "c", violating Galileo's PoR.

Thanks.

well first of all, for 1. you would want to say yes is not possible since Einstein didnt wanna violate maxwell but this one did satisfy galileo. 2. is for galileo as you noted. If 1. and 2. both have to be true then it leads to his conclusion. (this is not your question just a side note on how to respond)

As for how we know galileo is right it's because we can test it in real life and we know he is right (ofc we cant ever get a true inertial frame but we get close enough) --> there is other explanations for this with regards to particle accelerators but it is outside the scope of the syllabus

 

[dumNerd]

this is just rote learning lol, i genuinely don't think the markers look for actual knowledge in responses

when you are explaining the mirror and train thought experiment and related questions it is always clear which students know what they are talking about

 

[Trial&Error]

well first of all, for 1. you would want to say yes is not possible since Einstein didnt wanna violate maxwell but this one did satisfy galileo. 2. is for galileo as you noted. If 1. and 2. both have to be true then it leads to his conclusion. (this is not your question just a side note on how to respond)

As for how we know galileo is right it's because we can test it in real life and we know he is right (ofc we cant ever get a true inertial frame but we get close enough) --> there is other explanations for this with regards to particle accelerators but it is outside the scope of the syllabus

Hmm. I guess that does make sense. So would we say that "since experimental evidence shows that Galileo's principle is always true, it led to Einstein concluding the answer is Yes" ? And in order to satisfy Maxwell's predictions, he also added that c is an absolute constant for all observers and in vacuum, thus leading to his principle of special relativity?

Thanks again.

 

[dumNerd]

Hmm. I guess that does make sense. So would we say that "since experimental evidence shows that Galileo's principle is always true, it led to Einstein concluding the answer is Yes" ? And in order to satisfy Maxwell's predictions, he also added that c is an absolute constant for all observers and in vacuum, thus leading to his principle of special relativity?

Thanks again.

you dont need to say anything i was just explaining it . you just say it contradicted the galilean principle of relativity thus einstein concluded it wasnt true

 

[wizzkids]

Galileo's Principle of Relativity is not always true. Where did you get that idea from?
Galileo's Principle of Relativity is true for two observers in the same inertial frame of reference.
it is not true for observers in different inertial frames of reference, and the error gets bigger and bigger the closer the relative speed approaches the speed of light.
It is approximately true for two observers whose relative velocities are small compared to the speed of light.
You should look up the relativistic equation for addition or subtraction of velocities, and you should see that it approaches to Galilean relativity at low velocities, but at high velocities it imposes an upper speed limit in accordance with Special Relativity.

 

[dumNerd]

Galileo's Principle of Relativity is not always true. Where did you get that idea from?
Galileo's Principle of Relativity is true for two observers in the same inertial frame of reference.
it is not true for observers in different inertial frames of reference, and the error gets bigger and bigger the closer the relative speed approaches the speed of light.
It is approximately true for two observers whose relative velocities are small compared to the speed of light.
You should look up the relativistic equation for addition or subtraction of velocities, and you should see that it approaches to Galilean relativity at low velocities, but at high velocities it imposes an upper speed limit in accordance with Special Relativity.

i mean for HSC purposes she isn't wrong in saying that and would be awarded marks nonetheless (the teachers teaching this or marking it don't know any better) - GPR iworks perfectly fine in the classical low-velocity world Einstein just generalizes it so it still works when you bring high and low velocities into the picture.