What is the single best available explanation of relativity for the (intelligent) non-physicist?

Question

I've tried SOOO many - Simon Singh, Hawking etc etc and I still don't even really get that 'stretched surface with a grid on it' analogy!

Answer 1

The problem is that relativity is such a massively complicated subject, it really takes an experienced physicist to fully grasp it - so don't beat yourself up if you struggle to understand it as most people don't.

The stretched rubber sheet analogy refers to General Relativity. With this Einstein theorised that space and time together formed a 4th dimension, known as space time. Space time can be warped, and it's this warping that results in gravity. Imagine two people holding a rubber sheet (representing space-time) pulled taut between them. Then a third person comes along with a cannon ball and places it in the middle. The sheet will remain taut, but will dip slightly in the place where the ball rests. If we then roll another smaller ball towards the cannon ball, it will fall into the dip. This is, in essence, how gravity works. It is not really a kind of magnetism, as most people assume, it is actually a direct effect of the warping of space-time by very large objects of mass like planets.

And that, probably, is as far as any non-physicists can ever really get towards understanding that aspect of relativity.

Then of course, there's Special Relativity - and that deals with the very strange way that light travels within the universe, and what it means to our understanding of time.

Before Einstein it was assumed that time ticked on for all of us at the same rate and speed regardless of our circumstances. Didn't matter where you were or how fast you were travelling, time was time was time. Two synchronised watches would always stay synchronised. But relativity shows that, actually, that's not the case. It entirely depends on how fast you are travelling but ONLY relative to an observer.

Imagine that you're in a car that's travelling at 30mph, and I am standing at the roadside watching you approach. If you throw a ball out of the window at me as you go past at, say, 10mph then we would have a different perspective on how fast that ball was actually travelling. To you, in the car, the ball is travelling at 10mph - but to me, it's 40mph. You are already travelling at 30mph, so you would measure the velocity of the ball at 10mph, but I would have to take into account the speed of the car and add it onto the speed of the ball to get the true velocity.

This is quite simple and straightforward. But where it gets complicated is when we understand that the light that is travelling from the car's headlamps does not behave that way. It is entirely different. From both our perspectives light travels at exactly the same speed, without variation. Your car could be travelling at 100,000 mph, but light would still flow on from it at the same rate - you do not add on the car's speed to get the true velocity as you would when trying to judge the balls true speed. Regardless of your movement, or lack of it, the speed of light remains constant. And light travelling towards me comes at the same speed whether it's from a car travelling at 30mph, or a rocket at 100,000mph.

Einstein then theorised that if the speed of light does not change, then something else must. We know that in order to work out the speed of anything we need to divide distance covered by time taken. So it must be distance and time that change. And they do - but, again, only relative to an observer.

The faster an object travels the more time slows down, and the more the object will shrink - but ONLY from the perspective of any observer, and not from the perspective of the object itself.

Best way to envisage this is the train analogy. I am on a train platform, and you are on a train travelling at a velocity close to the speed of light. As you zoom past me, I will see that the train appears much shorter than it did at the beginning of the journey, and if I look through the windows I will observe that time has slowed down for you - your watch will be running slower, your movements will appear sluggish, and your voice, if I could hear it, would sound slurred.

But, to you, none of these effects would be evident. It's not just that you don't notice, but from your perspective, there's nothing to notice. If you were to look out the window at me it would be my time that had slowed, my watch that was running slower.

In essence, it's all relative.

I've gone on a bit, I know, but I hope I've helped.

Answer 2

Disclaimer: i'm no longer a physicist. those are no longer postulates, those are outcomes: - time dilation / length contraction - Gravitational time dilation / gravitational lensing - Mass–power equivalence The postulates are: - physics is the comparable regionally - the linked fee of light is the comparable value c regionally - acceleration by rocket is precisely the comparable as acceleration by soil, for equivalent values Your factors do no longer clarify something. you utilize "a approach or the different" at key moments to coach you haven't any longer have been given to any extent further clue than something human beings. And we do understand that the electron is a element particle, and could't be subdivided. And we do understand how plenty power an electron represents. on your lifetime, you may have many electron/positron pair annihilation activities on your physique, and the Earth and you're nevertheless right here. Relativity fails to describe the Universe, once you get to the dimensions of molecules. as a results of fact physics then variations from a non-end approximation (required for fundamental and differential calculus), to discrete. this could be a failing of Relativity, no longer a power.

Answer 3

The stretched surface on a grid thing is an explanation of the theory of gravity that comes with relativity (Gravity being defined as a deformation of the geometry of space as opposed to an actual force caused by the exchange of particles between two objects).

Relativity, as a math problem, has been around for a while. Even Galileo and Newton tackled it. A modern analogy usually involves a train or an airplane:
The train is moving at 100 km/h relative to the ground. You are on the train and throw a baseball at 100 km/s (relative to you) in the same direction as the train is going.
At what speed is the ball travelling relative to the ground? Newtonian relativity simply says: 100 + 100 = 200 km/h

Now get on a fast plane, travelling at, let us say, 10 km/s relative to the ground. Turn on a flashlight pointing forward and shooting out light at 300,000 km/s (relative to the flashlight). According to Newtonian relativity, observers on the ground should clock the photons at 300,010 km/s.

Meanwhile, at the turn of the century (19th to 20th), physicists were conducting experiments with light, measuring wavelengths in some experiments and mesuring the frequency in other experiments. They were noticing that whenever the wavelenghth got longer, the frequency would diminish in some predictable way. They noted that it looked like there may have been a "preferred" speed for light.

Equations for light measured by the observer travelling along with the source were simple and yielded what looked like a constant speed or, at the very least, speeds contained in a small interval.

Equations to explain how light would be perceived by observers in another frame of reference (as in our airplane thought-experiment above) turned out to be extremely complicated. They certainly did not follow Newtonian relativity (simply add the two speeds).

Meanwhile, also, Lorentz had worked on the idea that time is not perceived in the same way by people who travel fast than by people who are at rest.

Einstein brought everything together by supposing that maybe light has the same speed, whatever the frame of reference of the observer, and that the trick was in the flow of time experienced by the different observers. However, this reduced flow of time would cause apparent concentration of energy perceived as color shift in photons (e.g., more energy instead of more speed) or increase in mass for matter (which, using E=mc^2 is just a form of energy).

This gave space a geometry (in the mathematical sense) that varied according to the speed of the observer and the mass of an object. The "stretched surface" simply comes as an analogy that tries to help us understand how the mathematical geometry of space-time can affect calculations.

Answer 4

If you are prepared to tackle a straightforward account written for learning and not for entertainment, you could do no better than read Einstein's popular book:
"Relativity. The Special and the General Theory",
Methuen,
ISBN 0 416 67600 6
This is written in understandable language with the minimum appeal to mathematics. I found it to be an excellent cover of the Special Theory but, perhaps, a little short on the General Theory.

Answer 5

Ah Sexy Boy, but what are those billions of atoms made of, huh?
Space & Energy, oh and maybe tiny tiny multi-dimensional vibrating strings! And we get confused by gravity & a constant speed of light.

To the original question; I think there have been some good documentory films made on this stuff. Try BBC Horizon archives, or Equinox (C4, I think). ~They work well to compliment Singh & Hamkin's books.

Answer 6

It's a misconception that only intelligent people can grasp relativity. I managed fine.

What you need to do is think less, forget everything you think you know about the world around you and just accept the results for what they are. Once you have done that, then try to grasp the workings of it.

That's how my tutor told me to do it and it worked first time.

Answer 7

Paul Davies worte a book called about time....really easy to understand......as I like you am into physics without all the e=mc2 formula stuff happening. He has I am sure written more about the above.....really the best written stuff...ps...hawkins editor should be shot...that last book... the universe in a nutshell reads like a copy of the guardian newspaper. Panda eats shoots and leaves and all that jazz.

Answer 8

If you sit on a hot stove for 1 minute, it seems like an hour.
If you sit with a hot girl for an hour it seems like a minute.

And the following, I thought it also had somethnig to do with relativity.

Why is it so funny when donald duck sits in a little sail-boat and blows himself forward?
And why isnt this possible?

Answer 9

Okay seriously, the streched grid on a surface? BULLSHIT DUDE
Take the rubber sheet between two people put a cannonball in ththe middle and it dips, right? well yes, but in 'theory' would that same peice of rubber not dip if that same cannonball was placed in the middle if the rubber was NOT stretched? all from the point of the observer they say. THEY were all working with a 'stretched' peice of rubber. think it over

Answer 10

Say you have a really, really big clock. You travel away from it at the speed of light, but to you the hands appear motionless. So as time goes on for you, where the clock is, time stands still. That's relativity.