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**MathsIsFun****Administrator**- Registered: 2005-01-21
- Posts: 7,686

I have drafted an Introduction to Relativity: Relativity

Criticisims, correction, comments all welcome.

I want to get it right before publishing on website!

"The physicists defer only to mathematicians, and the mathematicians defer only to God ..." - Leon M. Lederman

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**Alg Num Theory****Member**- Registered: 2017-11-24
- Posts: 339
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It’s a good article. Here are a few of my suggestions.

Firstly, I think the little story between Alex and Sam can be omitted. I don’t see how it’s relevant to relativity – more like having to do with theories of expanding space (e.g. by viewing 3D space as embedded in a larger 4d hyperspace – much like the 2D surface of a sphere is embedded in 3D space).

Secondly, I would mention that things like length and mass also depend on speed: the faster an object moves relative to an observer, the shorter (in the direction of motion) and more massive the observer will measure it to be.

And thirdly, you didn’t mention the most famous equation in all of physics: *E* = *mc*²! Most people who are not familiar with special relativity may still be familiar with this equation, so I think it would be a give them some background information on it.

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**MathsIsFun****Administrator**- Registered: 2005-01-21
- Posts: 7,686

Thanks!

The reason for the little story is that most people think "Big Bang" which gives them a false idea of a central expansion point, and I want them to know the Universe is more elegant than that.

Isn't length contraction just a way of handling certain problems and not really a thing?

And how do I work E=mc² into it?

"The physicists defer only to mathematicians, and the mathematicians defer only to God ..." - Leon M. Lederman

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**ganesh****Administrator**- Registered: 2005-06-28
- Posts: 26,308

Hi MathsIsFun,

The page on 'Relativity' is almost perfect!

I feel all relevant information has been included.

A suggestion : Please add a paragraph on time dilation. That would make the page complete in totality.

It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

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**Alg Num Theory****Member**- Registered: 2017-11-24
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MathsIsFun wrote:

And how do I work E=mc² into it?

It comes from the formula for relativistic momentum:

where *p* is momentum and *m*₀ is rest mass. Simply put *p* = 0 for a particle at rest.

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**MathsIsFun****Administrator**- Registered: 2005-01-21
- Posts: 7,686

Thanks guys.

"The physicists defer only to mathematicians, and the mathematicians defer only to God ..." - Leon M. Lederman

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