Question on syllabus (1 Viewer)

[Lugia]

Hi,
This is a point which I don't know how to study for:
"Analyse and interpret some of Einstein's thought experiments involving mirrors and trains and discuss the relationship between thought and reality"

The only thought experiment that we learnt about is the relativity of simutanity. And that only involves trains but not mirrors...
And what do they mean by discuss the relation between thought and reality anyway?

And do we need to know how they got those 2 equations? Cause I think all the text books dervive them but cause I don't understand the maths I don't really want to learn them... so just wondering whether we need them...

Thanks!

 

[Dario]

The mirror experiment is just after the train door experiment in the Jacaranda textbook. The mirror experiment also happens on a train. Also, you don't need to derive the equations.

 

[Dumbarse]

the train with mirror experiment is this.

say your in a train travelling the speed of light and you are holding a mirror 1 metre away. could u see your reflection? if an outside observer sees the mirror carrying your reflection, could he be able to see your reflection. do the different frames of reference make a difference?
remember the train is travelling the speed of light, and the light to hit the mirror AND return back to u so u can see it can only travel the speed of light,
its a thought experiment so think about it...
in thought u cant see your reflection, in reality u can

 

[-=«MÄLÅÇhïtÊ»=-]

how can u assume in reality u can?
no train atm can travel at speed of light

 

[Dario]

That's why they call is a thought experiment !

 

[kini mini]

Thought experiments are extrapolations from what you already know. Einstein was so sure that the Principle of Relativity held that he took the extreme "Gedanken" of the train at the speed of light and the mirror and said that contrary to the classical theory you should be able to see your own reflection. No train can travel at the speed of light, or probably will ever travel that fast (even if we can get a vehicle going that fast, which seems doubtful, I'm sure it won't be a train!), but the whole idea is using your imagination to extrapolate.

 

[Lugia]

See that's the one that I don't understand, the one about whether u can see ur own reflection... I mean if u can see it, then the person out side would see light going at 2c... this doesn't make sense!!!!

 

[Dario]

Remember that Speed = Distance / Time

So,
If the speed is same in both frames of reference, then the distance and time must be changing ! That is, 'time dilation' and 'length contraction.'

 

[Lugia]

Well then why didn't einstein thought that it could be the other way round? like time contract and length dilate? (sorrie wierd wording!)

 

[McLake]

Originally posted by Lugia
Well then why didn't einstein thought that it could be the other way round? like time contract and length dilate? (sorrie wierd wording!)

I don't know if this is true, but maybe because then t --> 0 which is not calculatable?

 

[BlackJack]

Time dilation and length contraction comes from how everyone sees light as travelling at c.

Consider travelling (high fraction) light speed going past a building, what would you see?
Draw arrows of light from the building and draw yourself travelling at, say half the speed of light and point these at some point when they all meet.

But, what's the point? Looking at this, the angle of the lgiht to your path isn't the direction you actually see it in. To get the real direction, take the path you have travelled, measure back along it half the distance to whatever part of the building you 'see' from the meeting point. Draw line between the part of the building and the new position. That's the direction. If you do this to all the points on the building, you get the image* you see at half light speed, except you see that image at the meeting point.
The building should look narrower and 'rotated'. That is length contraction.

Edit: you'll have to transpose the new lines to get them to meet at the same point again.

I'lll do time later

 

[BlackJack]

As for the 2 equations, I certainly hope we don't need to know how to derive them... I'm kinda thinking that's for uni later on.

 

[Lazarus]

You don't have to know how to derive the equations.

 

[-=«MÄLÅÇhïtÊ»=-]

"See that's the one that I don't understand, the one about whether u can see ur own reflection... I mean if u can see it, then the person out side would see light going at 2c... this doesn't make sense!!!!"

That is why time dialates

 

[1234567]

think abotu it this way.

because t = d/v
and according to einstein, v = c, which c is constant at all times,
using that equation for this situation, means that if c remains constant, then the value taht's different for the observers must be time!