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2 points

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9th May 2021

a great book on GR i like is called "Why does E=MC^2" written by Dr. Brian Cox and Jeff Forshaw. they tell you when you can skip a head if you don't want to go through all the math, and they really break it down. almost like ELI16

1 point

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3rd Feb 2015

You might like the book Why Does E=mc2? (And Why Should We Care?). It does a pretty good job of explaining all this without too much math (there is some relatively simple math, but you can skip it if you prefer).

18 points

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18th Apr 2018

What you've said is mostly close enough that the difference doesn't matter much to a layperson. However this bit:

> Light does not pass through time (which doesn't make sense to me, but I read that somewhere) which is why it is always moving through space at the speed of light.

Is a bit off while also being a very interesting topic. I imagine the source of this statement is related to the fact that photons will always travel at the speed of light, relative to *all* observers. In other words, if I were to travel towards you at 0.5c, then shine a light towards you, the light would travel away from me at c while simultaneously (from your point of view) approach you at c, not 1.5c.

In essence, if you assume it to be true that the light moves away from me at c, and towards you at c, the only way to reconcile the two statements is that we experience time differently.

This incidentally is a really good starting point for learning about General Relativity (I heartily recommend the book Why Does E = mc² (and Why Should We Care?) if you find this interesting as it does a way better job of explaining it than I could).

One good example from that book is a thought experiment where you have two observers. One observer is on a train. He has with him an extremely precise clock that simply bounces photons from one plate (bottom) to another (top). For this observer, the photons are going completely vertically as long as the train is NOT accelerating. It critically *does not* matter whether the train is moving relative to the ground or not, only whether it's accelerating or not. However, to the observer on a platform as the train goes by, the position of the photon as it bounces off the bottom plate, is not directly below the point at which it hits the top plate. It's very close, as the train is not traveling at relativistic speeds, but it's definitely not directly above (picture it as a right angled triangle where the light just traveled the hypotenuse).

This means that even in something traveling relatively slowly, the light has traveled *further* for the observer on the platform, than for the observer on the train, despite being exactly the same photon traveling at exactly the same speed (c). How much further the light traveled depends on the relative speed. One of the interesting things about this though is that the time dilation effect is actually real and measurable even at relatively slow—certainly achievable—speeds. In fact, it actually effects things we use every day. Flights for example are fast enough that it's measurable, but more interestingly, GPS would not work for more than a few days at a time if the satellites we put in orbit for it to function did not take this effect in to consideration!

1 point

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21st Feb 2021

They could, that’s an equally valid point of view as well!

But anywhere there is no experiment that can determine whether you are in motion or not.

> Galileo's principle of relativity states "It is impossible by mechanical means to say whether we are moving or staying at rest". If two trains are moving at the same speed in the same direction, then a passenger in either train will not be able to notice that either train is moving. However, if the passenger takes a fixed frame of reference, a fixed point, like the earth, he will then be able to notice the motion of either train. Another thing, if one stands on the earth one will not be able to see that it is moving.

https://simple.m.wikipedia.org/wiki/Principle_of_relativity

If this stuff interests you I highly recommend this book: https://www.amazon.com/Why-Does-mc2-Should-Care/dp/0306818760/ref=nodl_

It goes through the history of relativity and all the way through how Einstein formulated his theories. It walks you through it and holds your hand very well even if you don’t have much math or physics background.

1 point

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9th Aug 2020

"Why e=mc^2 and why you should care" by Brian Cox and Jeff Forshaw

Very good book if you want to grasp the fundamentals of spacetime.

https://www.amazon.ca/Why-Does-mc2-Should-Care/dp/0306818760

1 point

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7th May 2015

See if you can get your hands on this:

As other people have said its gonna be a while before you can get to grips with this stuff properly, but that book gives a gentle introduction to the maths without being too intense.

This is also worth a look if you're thinking about studying physics later

1 point

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26th Sep 2012

1 point

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2nd Nov 2010

I just read Why Does E=mc2?: (And Why Should We Care?) by Brian Cox. Can't say I fully understood it all (only an amateur physics buff) but found it very interesting.

0 points

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18th Apr 2013

**Why Does E=mc2? (And Why Should We Care?)** (List Price: $15.95)

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