Einstein's Theory Of Relativity Made Easy

http://facebook.com/ScienceReason ... Albert Einstein's Theory of Relativity (Chapter 1): Introduction.

The theory of relativity, or simply relativity, encompasses two theories of Albert Einstein: special relativity and general relativity. However, the word "relativity" is sometimes used in reference to Galilean invariance.

The term "theory of relativity" was coined by Max Planck in 1908 to emphasize how special relativity (and later, general relativity) uses the principle of relativity.

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SPECIAL RELATIVITY

Special relativity is a theory of the structure of spacetime. It was introduced in Albert Einstein's 1905 paper "On the Electrodynamics of Moving Bodies" (for the contributions of many other physicists see History of special relativity). Special relativity is based on two postulates which are contradictory in classical mechanics:

1. The laws of physics are the same for all observers in uniform motion relative to one another (principle of relativity),
2. The speed of light in a vacuum is the same for all observers, regardless of their relative motion or of the motion of the source of the light.

The resultant theory agrees with experiment better than classical mechanics, e.g. in the Michelson-Morley experiment that supports postulate 2, but also has many surprising consequences. Some of these are:

• Relativity of simultaneity: Two events, simultaneous for one observer, may not be simultaneous for another observer if the observers are in relative motion.
• Time dilation: Moving clocks are measured to tick more slowly than an observer's "stationary" clock.
• Length contraction: Objects are measured to be shortened in the direction that they are moving with respect to the observer.
• Mass-energy equivalence: E = mc2, energy and mass are equivalent and transmutable.
• Maximum speed is finite: No physical object or message or field line can travel faster than light.

The defining feature of special relativity is the replacement of the Galilean transformations of classical mechanics by the Lorentz transformations. (See Maxwell's equations of electromagnetism and introduction to special relativity).

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GENERAL RELATIVITY

General relativity is a theory of gravitation developed by Einstein in the years 1907--1915. The development of general relativity began with the equivalence principle, under which the states of accelerated motion and being at rest in a gravitational field (for example when standing on the surface of the Earth) are physically identical. The upshot of this is that free fall is inertial motion; an object in free fall is falling because that is how objects move when there is no force being exerted on them, instead of this being due to the force of gravity as is the case in classical mechanics.

This is incompatible with classical mechanics and special relativity because in those theories inertially moving objects cannot accelerate with respect to each other, but objects in free fall do so. To resolve this difficulty Einstein first proposed that spacetime is curved. In 1915, he devised the Einstein field equations which relate the curvature of spacetime with the mass, energy, and momentum within it.

Some of the consequences of general relativity are:

• Time goes slower in higher gravitational fields. This is called gravitational time dilation.
• Orbits precess in a way unexpected in Newton's theory of gravity. (This has been observed in the orbit of Mercury and in binary pulsars).
• Rays of light bend in the presence of a gravitational field.
• Frame-dragging, in which a rotating mass "drags along" the space time around it.
• The Universe is expanding, and the far parts of it are moving away from us faster than the speed of light.

Technically, general relativity is a metric theory of gravitation whose defining feature is its use of the Einstein field equations. The solutions of the field equations are metric tensors which define the topology of the spacetime and how objects move inertially.

• http://en.wikipedia.org/wiki/Theory_of_relativity

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[0ester]

Why is this labeled as Einstein's Theory of Relativity? It does not even touch his theory, except at the end where it says, that classical relativity does not work at high speeds. This should be "Classical Relativity Made Easy"

[tonycatman]

Why does everyone always say that Satnav needs Einstein's relativity to work ? I worked for navman for two years, and I can tell you that we used Pythagoras. Is it a conspiracy ?

[HappyHouseFilms]

Sarah just think's that so god damn hilarious, dosen't she.

[tonycatman]

@SavageJim01 Quick calc, then. How long do you think it takes for light to bounce from a geo-stationary satellite ? How far could a car travel in that space of time ? I reckon a max of 50 metres out, given the furthest satellite and max vehicle speed.

So you might adjust for the speed of light, but this is quite a different thing from acknowledging that the speed of light is a constant from every frame of reference, or using complex counterintuitive maths .

[ogiugi96]

CHANGE TO FUCKING METRIC SYSTEM! Considered guy from Serbia!

[SavageJim01]

@tonycatman It's because you are told to round off the errors. They are small for your purposes and can be discounted at your part of what you do.

Your calculations might be okay for calculating instantaneous position assuming instantaneous signal transmissions, but considering the distances and time for light to move as well as the movement of the Earth vs the movement of the satellite, that error becomes significant when calculating what position the sat will tell you.

[tonycatman]

@dookdawg214 To work, the system needs three out of a number of satellites. All of them are moving, and often, so is the vehicle.

The light speed delay is inconsequential in comparison to the speed of movement of the four points, and the system adjusts accordingly. The satellites are really not that far away.

A predictive speed model for the vehicle is used either way, and this is the thing which requires the greatest adjustment.

[dookdawg214]

@tonycatman

Pythagoras requires three fixed points, which you don't have in GPS tracking. A satellite in space -- or a receiver high up -- is not moving at the same speed as a fixed point on earth. So, by the time it takes for the data to go up and come back down -- if the system considers everything on the same time scale, which it's not -- your orginal fixed point is now farther away. Relativity recalculates to account for this lag.

[godzillaleas]

my brain hurts.

[alanspicertelecom]

@0ester If you were stupid ... and you were going 60 mph in a car ... you will still be stupid. But others would perceive you as moving towards greater stupidity even faster.

[imasickkunt01]

Sarah you slut