I have tried to get my head around relativity for years but it never seems to .....?

Question

have twigged. All the books I have tried to read seem to assume too much prior knowledge. Can some one explain it or point me to a site that can explain it in idiot terms.

Thanks guys

Answer 1

It's very simple. We are all six paces away from a bacon sandwich. If the sandwich includes lettuce and tomato then the odds are reduced to two paces. If the bacon isn't called Kevin but Harold than the proposition alters profoundly. The rule is 'Everything is relative if your uncle comes for a week but stays for two months.'

Answer 2

Hmm, let's see...

1. Speed of light in vacuum is constant.

2. Pretty much everything else in the Universe is relative to the frame of reference - time, distance, mass, etc.

3. Mass and energy are related to each other and can be transformed into each other, aka E = Mc2

That's relativity summed up for you.

Answer 3

Ok, imagine you are in a spaceship and there is no background stars. All you see is a black background with no fixed point of reference.

Now, you are traveling in a straight line and you open a trapdoor in the bottom of the spaceship. You throw a cricketball downwards out of the spaceship. What do you see happening (remembering you have no fixed point of reference to look at)?

You see the ball falling downwards away from you, straight down.

No consider what an independant observer would see. He sees you in your spaceship throwing the cricket ball as you pass him. What does he see?

He sees the ball moving both downwards and sideways at the same rate as the spaceship.

Its the same event but two different things are observed from different viewpoints. Which observer is seeing it correctly? How do you know?

What relativity says is that simply, whatever you see, whatever results you get, there can always be another observer viewing from a different velocity or position or distance that will see something completely different.

Answer 4

Here's relativity in the shell of a nut.  Time, space, and mass are relative and what you see of each one depends on the reference frame the observer is in.  

For example, if a spaceship travels v = 1/4 c, one quarter light speed, an observer outside the ship will see time and mass on the ship increase by 3% over what it was when the ship was standing still relative to the observer.  And the length of the ship will be 1/1.03 what is was when standing still.  And all this is relative to the observer standing outside the ship.

Meanwhile, back on the ranch...the space farers see nothing, hear nothing, and feel nothing...everything is normal as far as they are concerned.  The spaceship is still m mass, time still takes one second to tick off a second, and the length of the ship is still what it was before taking off.

And that's relativity...time, mass, and length are changed relative to the outside observer in the outside framework.  But inside, relative to the ship's framework, nothing's changed...time, mass, and length appear just as they did before takeoff.

Here are the relevent equations: T = t/L(v); M = m/L(v), and l = L L(v), where L(v) = sqrt(1 - (v/c)^2), which is called the Lorenta trasnformation.  t, m, and L are the rest time, mass, and length.  This simply means these are the values when v = 0, the body m is at rest.  T, M, and l are the relativisitic time, mass, and length...they are simply their rest counterparts changed by the L(v) factor.

Answer 5

special relativity depends on the experimental observation that the speed of light is constant in all reference frames moving wrt to each other. (if u chase after a light beam in a rocket, it'll still be doin' 186,000mps). Also the laws of science are conserved in all reference frames moving wrt each other (eg cons of momentum, F=ma etc). The only way to achieve both is that the observed fundamental quantities like mass, length and time have to vary between moving frames and in proportion to their relative speed according to the LT coeff..(1/rt(1-v^2/c^2). If u binomially expand this expression for the mass transform u get E=moc^2.

For Gen Rel u can show that there is no experimental way of distinguishing between a local uniform grav field and an acceler8ed ref frame (lift gedankenexperiment). This means that light bends in  a grav field as it would as if it crossed the path of an lift acceler8ing upwards say, because the laws of science in each are indistinguishable. This means among other things that massive bodies 'bend' spacetime in their vicinity. The speed of light is absolutely constant, so the space through which it travels has to deform in order to accomad8 (just as M,L,T did 4 Spec Rel).

This eventually leads to gravitational time d4m8ion,the black hole and the freezing of time beyond the Schwartzchild surface surrounding its singularity.

Answer 6

The Special Theory of Relativity was published in 1905 and deals with (frames of reference) objects separating with constant high velocities (close to the speed of light). In this first theory, Einstein stated that the speed of light was the absolute limit for all velocities and furthermore all observers, what ever their motion, must measure the speed of light to be exactly the same. Finally, only mass-less objects may attain the speed of light. However, massive objects contract in their direction of motion, their clocks slow down relative to observer's clocks and they gain mass and thus inertia as they accelerate towards the speed of light.

Einstein's theory of General Relativity (1915) is a cause and effect theory. The theory describes the fabric of space-time as a medium that may be distorted by the presence of mass and energy. From his earlier relativity theory, Einstein had related mass and energy in the famous equation: -

E = mc²

From this concept, he described the curvature or distortion of space-time as due to the total sum of mass-energy present within the region of distorted space. It is the curvature of space-time we call gravity. Thus, our planet follows the 'straightest' path or path of least action whilst it orbits the mutually curved space around the Sun. An object falling to earth, under the pull of gravity, is following the curvature of space in the region around the surface of the Earth. Einstein described the relationship between space-time curvature and the mass-energy causing it, in the tensor field equation: -

G = 8πT

Where 'G' is the Einstein tensor representing the 'gravity' or curvature of space-time and 'T' is the total energy tensor representing the mass-energy creating the gravitational curvature of the space-time.

The theory, accurately predicts many features of the solar system, such as the peculiar motion of Mercury’s perihelion, and may be used to account for the gravitational physics of black holes and neutron stars. The extreme high pressure physics at the core of a star may be described using this theory. General relativity also predicted the Big Bang origin of the universe, although Einstein refused to accept the conclusion. He later claimed that this erroneous conclusion was his biggest blunder. Overall, after ninety-three years, General Relativity is still the best theory of gravity that we have!

Answer 7

you can measure something. anything, a length, a period of time, whatever.  and someone else can measure the same thing.

the 2 measurements can both be CORRECT and DIFFERENT at the same time.  

because you both have a different frame of reference.  like, how you look at it...

in special relativity the difference is due to the relative speeds of the observers.  in general relativity its to do with accelerating reference frames

good luck