Presentation onSpecial Theory of

Relativity

By :-

Vishal Thakur

The Special Theory of Relativity

(published in 1905 by Albert Einstein)

• Aimed to answer some burning questions:– Could Maxwell’s equations for

electricity and magnetism reconcile with the laws of mechanics?

– Where was the Luminiferous aether ?

(null result of 1887 Michelson–Morley experiment)

Postulates of Relativity :

First

“The laws of physics are same for all the observers in uniform motion relative to each other”

Second“The speed of light in vacuum is same

for all the observers, regardless of their relative motion or of the motion of the source of the light”

(Speed of light c = 3 x 108 metres/second = 670,616,629 mph)

Facts of Relativity• Regardless of speed or direction, observers

always measure the speed of light to be the same value.

• Speed of light in vaccum is the maximum possible speed.

• Generalizes Galileo's principle of relativity —all uniform motion is relative, there is no absolute and well-defined state of rest.

• Consequences of the theory confirms Lorentz Transformations and mostly

are related by Lorentz factor

CONSEQUENCES :-Relativity of Simultaneity

• Events which are simultaneous in one frame may not be in another!

• Each observer is correct in its own frame of reference.

Time Dilation• Time lapse between two events is not

invariant to observer, but depend on the relative speeds of the observers reference frames.

• Observer measure moving clock run slow.• Example – Twin Paradox (concerns a twin

who flies off in a spaceship traveling near the speed of light and returns to discover that his or her twin sibling has aged much more)

Length Contraction

• Observers measure moving objects to be shorter than they were at rest.

• Only applies to the direction parallel to the motion on objects moving near to the speed of light!

1 + 1 not equals to 2• Velocities(and speeds) do not simply add

up.

• Also called composition law for velocities.

• For collinear motions of two objects (u and

v as their velocities),the velocity of each object relative to a stationary observer is :-

• Isn't noticeable at low velocities but as the velocity approaches the speed of light it becomes important.

Thomas Rotation

• Orientation of an object (i.e. the alignment of its axes with the observer's axes) may be different for different observers.

• Unlike other relativistic effects, this effect becomes quite significant at fairly low velocities as can be seen in the spin of moving particles.

E = mc2

• Famous Mass-Energy equivalence…– This is also the Rest Mass Energy of the

particle– Much amount of energy is released when a

relative small amount of mass gets lost! 

• Important consequences:– nuclear fission (as in atom bombs)…– nuclear fusion (as in sun and other stars)!

How does SR help us?• Mass Energy Equivalence

– Particles can annihilate with their antiparticles, releasing much energy.

– Production of new particles!• Time Dilation– Allows particles to travel much further than

previously expected.– Easier to detect and identify particles!• Spacetime– Space and Time – now considered different

components of single entity.– Divided in different ways by observers in relative

motion.

How does SR hinder us?• Accelerator beam energy must be high enough

for the mass of particles you want to produce.• Need to have long acceleration times than

expected.•SLAC(Stanford Linear Accelerator Center) accelerator needs a 3-km path to get speed that Newtonian dynamics predicts for 1.5 cm!

•LHC (Large Hadron Collider - world's largest and highest-energy particle accelerator ring) diameter = 27 km!

Summary• 2 postulates, strange consequences

– Relativity of simultaneity– Time dilation– Length contraction– Composition of velocities– Thomas Rotation– Mass - Energy Equivalence – Spacetime

• Particle physics– Production of new particles– Easier to measure, harder to accelerate