2.32.3EINSTEIN EINSTEIN

AND AND RELATIVITYRELATIVITY

2.32.3EINSTEIN EINSTEIN

AND AND RELATIVITYRELATIVITY

Special Relativity

Albert Einstein (1879-1955)

Determined Newton’s Laws of Motion are only correct for low velocities, ones much less than the speed of light.

His analysis led him to the first postulate of relativity (principal of relativity):

1st Postulate:

Observers can never detect their uniform motion except relative to other objects.

Train example

Special Relativity An alternate version states:

The laws of physics are the same for all observers, no matter what their motion, so long as they are not accelerated.

Special Relativity

If either spaceship were to fire its rockets, it would be accelerated because its velocity would change.

The crew would feel this, pressing them into their seats.

Accelerated motion is different, therefore this postulate applies only to the “special” case of observers in uniform motion, which means unaccelerated motion.

Therefore, this theory is known as the special theory of relativity.

Special Relativity

Einstein also came to the conclusion that the speed of light, c, must be constant for all observers. This became his second postulate of relativity.

~ 300,000 km/s ~ 186,000 mi/s

2nd Postulate:The speed of light is constant and will be the same for all observers independent of their motion relative to the light source.

Discovery Time

From this, Einstein was led to some startling discoveries. Concluded Newton’s Laws of Motion and Gravity worked well as

long as distances were small and velocities were low. Observed the mass of a moving particle depends on its velocity. Higher the velocity, the greater the mass.

Observed when physicists accelerate atomic particles to high velocities.

Large Hadron Collider Large Hadron Collider (LHC)(LHC)

Constructed by the European Nuclear Constructed by the European Nuclear Research Centre (CERN) in Switzerland.Research Centre (CERN) in Switzerland.

Designed to simulate the effects of the Designed to simulate the effects of the Big-Bang and provide scientists a clear Big-Bang and provide scientists a clear understanding of the universe’s origin.understanding of the universe’s origin.

Discovery Time

The equations describing the energy of a moving particle predicts the energy of a motionless particle is not zero. Rather, its energy at rest is moc2 …

This shows mass and energy are related. Example:

Say you convert 1 kg. of matter into energy.

Result is 9.0 x 1016 joules (J) approx. equal to a 20-megaton nuclear bomb (lots of energy from a small mass).

c = speed of light; 3 x 108 m/s

m = mass of the particle at rest

Effects of Special Relativity

Length Contraction (Lorentz-Contraction) – length scales on objects at or nearly approaching the speed of light appear shortened.

Movement: 10% speed of light

Movement: 86.5% speed of light 1/2 original length

Movement: 99% speed of light

1/7 original length

Movement: 99.99% speed of light

LENGTH (Lorentz) CONTRACTION

Effects of Special Relativity

Time Dilation – since the speed of light, c, is constant, time moves slower for objects approaching light speed.

Time Dilation Video Clip

TIME DILATION

General Relativity

In 1916, Einstein published his general theory of relativity, dealing with both accelerated and uniform motion.

Concluded gravity and acceleration are related through the equivalence principle:

“Observers cannot distinguish locally between inertial forces due to acceleration and uniform gravitational forces due to the presence of massive bodies.”

General Relativity

The importance of general relativity shows how gravity, inertia, and acceleration are all associated with the way space is related to time. This unique relationship is known as space-time. Often referred to as curvature:

According to general relativity, mass tells space-time how to curve, and the curvature of space-time (gravity) tells mass how to accelerate.

Curvature Confirmation

Einstein’s general theory of relativity has been confirmed by a number of experiments. For example, the motion of light

through curved space-time near the Sun has been observed. The equations for general relativity

indicated light would have an extra deflection caused by curved space-time, just as a rolling golf ball is deflected by undulations in a putting green.

Star field observed months before a solar eclipse, then during the solar eclipse.

Appear to shift away from the Sun by 1.77”

Even Einstein loved Freeport …Even Einstein loved Freeport …

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