+ All Categories
Home > Documents > Measurement, Relativity, Einstein and Everything Else Michael Bass Professor Emeritus College of...

Measurement, Relativity, Einstein and Everything Else Michael Bass Professor Emeritus College of...

Date post: 03-Jan-2016
Category:
Upload: gilbert-tucker
View: 217 times
Download: 0 times
Share this document with a friend
25
Measurement, Relativity, Einstein and Everything Else Michael Bass Professor Emeritus College of Optics and Photonics, CREOL University of Central Florida © M. Bass
Transcript

Measurement, Relativity, Einstein and Everything Else

Michael BassProfessor Emeritus

College of Optics and Photonics, CREOLUniversity of Central Florida

© M. Bass

© M. Bass

The essence of science

Science differs from religion in that science deals with what can be measured/quantified.

This means that science requires standards of measurement.

In other words standard units that we can all agree upon. It means that if two different labs make a

measurement of some quantity they can trust that they are using the same yardstick, clock or mass.

© M. Bass

Length, time, and mass

All our units of measurement derive from just these three: Length – the meter Time – the second Mass – the kilogram

All others are derived units. In fact, many theories in physics are set up so

that the units are correct – both sides of the equations must have the same units!

© M. Bass

Newton’s Mechanics

You all remember F = ma (or more correctly F = m(dv/dt))

Here Newton connected the response of an object having mass, m now measured in kg, to the application of a force, F, – it would change its velocity, v, and accelerate at a measured in meters per second per second.

In fact, what Newton did here was define the unit of force now called the Newton and it is kg m/s2.

© M. Bass

Newton at a deeper level

Newton’s concept was that there was some universal reference frame against which all measurements could be referenced. It came to be known as the ether – a massless,

frictionless, undistortable coordinate system through which all things moved.

His mechanics and all that followed from them (thermodynamics, the industrial revolution, the ascendance of the west, the modern world and etc.) seemed to work with this assumption.

However, it proved to be wrong.

© M. Bass

Electromagnetics

By the end of the 19th century the work of Michael Faraday, James Clerk Maxwell, Carl Freidrich Gauss, Guglielmo Marconi and many others established that

Electromagnetic waves (everything from radio waves to visible light to gamma rays) were transverse waves traveling at the speed of light.

They carried energy and so could be useful. Could they be used to measure the earth’s

motion through the ether?

© M. Bass

Enter Albert Michelson

Michelson was a Professor of Physics at Case University in Cleveland. He invented an optical device (!!) – a Michelson interferometer with which he proposed to determine the earth’s motion through the ether.

mirror

mirror

Half silvered mirror

Monochromatic light source

Here there be fringes!!!

© M. Bass

The Michelson-Morely Experiment

Float a Michelson interferometer in a pool of mercury and hope you don’t go mad.

Point one arm in the direction of the earth’s movement around the sun.

While watching the fringes determine any change as the interferometer is rotated so the other arm points in that direction.

The change in the fringes would be a measure of the earth’s speed as it altered the light speed in the arms of the interferometer.

© M. Bass

The result

No change in the fringes. Either the earth was not moving or the speed of light did

not change according to the motion of the light source. The first could be ruled out so the second had to be true. But this violated the certainty of Newton’s assumption of

a universal reference frame. Light traveled at a speed independent of motion

through the reference frame so why did we need such an all encompassing assumption?

© M. Bass

Attempts to “save the model”

Lorentz in Holland and Fitzgerald in Ireland suggested that perhaps the arm in the direction of motion contracted – got shorter – so that the light actually only had to travel a shorter distance in this direction.

Except in Star Trek and Star Wars this contraction actually does occur when an object’s speed approaches that of light.

Just proposing the Lorentz transformation rules as he did, did nothing to deal with the fundamental problem There seemed to be no universal reference frame!! Why – what did it mean – was the universe so unlike

our expectations?As speed approaches that of light you get squeezed and become more massive. You also age more slowly.Slow, fast, faster, very fast

© M. Bass

Enter Albert Einstein (1879–1955)

In 1905 in Annalen der Physik there appeared 4 papers by an obscure patent clerk in Bern, Switzerland: One explained Brownian motion of particles. One explained the photo-electric effect. One explained special relativity. One explained mass-energy equivalence.

For any one Einstein could have won a Nobel Prize The paper on special relativity however was a major

turning point in the history of physics and in the story of our understanding of the world and the universe

Ever since we have to say “we live in a Newtonian world embedded in an Einsteinian universe.”

© M. Bass

Albert and Mileva

She was the only female physics student in his class. She was bright and interesting but

Did not pass her Ph. D. exams

They married, had two children and drifted apart. When he went to Berlin he struck up a

relationship with Elsa, his cousin, and his marriage got worse.

© M. Bass

The theory

Assumptions: There is no absolute reference frame. All observers in their own reference frames moving

with respect to each other must arrive at the same laws of physics.

Specifically, each observer must measure 2.997924589 x 108 m/s for the speed of light in a vacuum – a universal constant.

By assuming the speed of light to be absolute and unvarying Einstein was forced to conclude that space and time are relative.

Einstein claimed not to know of the Michelson-Morely result and that he just felt the universe must be this way. Since Michelson became the first American to win a Nobel prize in 1907 this claim seems unlikely.

© M. Bass

The results

From these simple assumptions he showed that length in the direction of motion got shorter time slowed down as you moved near the speed of

light, mass and energy were related by the famous

equation, E = mc2, Now mass-energy and not just mass or energy had

to be conserved (a re-write of the first law of thermodynamics), and

you could never travel faster than c His predictions have been tested experimentally and

they have never failed (except in science fiction) Ever since Einstein all physical theories that would be

of any use had to be relativistically invariant.

© M. Bass

Einstein’s critical thought experiment

Suppose I were on the rear platform of a train looking at a clock in the train station. While the train was still my watch and the clock would measure

the same time intervals. If my train moved away from the clock at some speed then the

light from the clock traveling at speed c would take time to reach me.

But the light from my watch would not take any time so I would think the clock at the station was running slower than my watch.

If my train were moving at speed c the light leaving the clock after I departed would never catch up. I would always see the clock as it was at the moment of departure. I would think the clock had stopped.

© M. Bass

Simple and Beautiful

It is worth noting that Einstein’s concept of a simple and beautiful set of laws to govern the universe might pass for certitude.

It actually leads to a 20th century of change and loss of causality.

Einstein for contributing to both relativity and quantum mechanics was both loved and reviled, as much for disturbing people’s peace of mind as for his brilliant contributions.

© M. Bass

General Relativity

After 1905 he spent time in Prague and then back to Switzerland. Then, Max Planck recruited him.

Einstein in 1914 moved to Berlin to the prestigious position of Professor of Theoretical Physics at the University of Berlin.

In 1916, at the height of World War I he published his theory of General Relativity – relativity when in accelerating reference frames. Gravity would bend light!!

In 1919, Sir Arthur Eddington measured the gravitational bending of light exactly as Einstein had predicted it.

© M. Bass

Albert and Elsa

In Berlin he re-connected with Elsa. She was the kind of supportive and stable wifely

woman he needed. He dictated to Mileva what she had to do to be with

him (for example, not to speak to him without being spoken to first).

Finally, a divorce was arranged when he promised Mileva his Nobel Prize money (which he had not yet won).

She returned to and lived in Bern with their children.

© M. Bass

Gravity bends light

Distant star appears at some location in space.

Earth Eddington Eddington – wow!! Albert was right.

Distant star appears shifted in location due to bending of light by the sun’s gravity.

Moon eclipses the sun

sun

© M. Bass

Black holes

If gravity can bend light then a very large gravitational field can bend light so much that it can not escape – this is a black hole. We have found black holes including a multi million solar

mass black hole at the center of our galaxy

Light that passes close by just gets bent.

Masses that pass by have their trajectories altered.

Masses or light that cross the boundary get sucked in. There is no escape!!

© M. Bass

Bending leads to lensing and other funny stuff

Multiple images

Einstein rings

Measures of distance

This really happens!!

© M. Bass

Expanding universes

Our universe is not static – it is expanding and has been since it started about 13.5 billion years ago.

At the time of creation gravity and the other forces were unified into one force.

Almost immediately gravity separated from the others and today there seems to be only 4 fundamental forces in the universe The strong nuclear force The weak nuclear force The electromagnetic force Gravity

© M. Bass

Gravity

All but gravity have been quantized so that they explain with incredible accuracy the observed universe.

Gravity is eloquently explained by Einstein’s General Theory of Relativity and defies quantization.

We just don’t know what happens inside a black hole where the force of gravity crushes matter into a singularity of infinite density.

But that was the universe at t = 0. Everything, all the mass-energy of the universe

was confined to a tiny volume. It was very dense and very hot

© M. Bass

So what happened

There must be another force, the force of the big bang, that could overcome gravity and create a universe that could eventually contain critters that could wonder how it all got started.

Sometimes called DARK ENERGY it may be why the universal expansion seems to be accelerating.

Einstein started the process but it is far from over and new observations such as an acceleration of the expansion must be taken into account.

This is the excitement of science and the demand for the scientist to continue to pursue the truth.

© M. Bass

Beyond science Einstein during his years in Prague became a pacifist.

This was a problem for him while in wartime Germany. After WW I his fame led him to other interests in particular, to be

a voice for other Jews who were being discriminated against and persecuted in Germany.

1932 he moved to the United States. Institute for Advanced Studies at Princeton He defected from pacifism in the face of Nazi criminality and, in

1940 signed the letter to Roosevelt that led to the

Manhattan Project and the nuclear weapons program. Interestingly enough, he never took part in the project.

In 1948 he was offered the Presidency of the new state of Israel but had the good sense to turn it down.

Died in 1955 without ever achieving a unified field theory since he was unwilling to apply quantum thinking to gravity. To date no one else has come even close.


Recommended