Albert Einstein had a problem with Isaac Newton’s laws of gravity and motion. For about 3 centuries humanity was satisfied with Newton’s assertion that gravity was a force that held the celestial bodies of the universe together. Einstein wondered how this idea could square with the fact that the speed of light can not be altered.
One thought experiment he entertained was what would happen to the solar system if the sun instantly lost the powerful force of gravity that Newton said it had. It takes a beam of light about 8 minutes to travel from the sun to the Earth. If gravity was a force, than the Earth should be thrown instantly to the depths of space if the gravity was cut off. (Much the same way if you swirl a string tied to a ball around your head and let go).
But gravity waves travel no faster than the speed of light. If the sun lost its gravity, it should take 8 minutes for the news to reach Earth. What would happen during these 8 minutes? Would the Earth continue in its orbit around the sun?
As a young man Albert Einstein wondered what would he would see if he ran parallel to the leading edge of a beam of light. If we look back to a discovery in 1821 we can find a clue to the answers of these questions. That year a Danish scientist discovered that when an electric current is passed through a wire, a magnetic needle will turn around at a right angle. Somehow electricity and magnetism were intertwined.
The experiment caught the attention of the son of a blacksmith named Michael Faraday. Faraday wanted to find out if a magnet could affect a wire and produce motion.
He found if you move a magnet through a coiled copper wire an electric current will flow through the wire. His research led to the invention of the electric motor and a new kind of physics – electromagnetism. His work got him into the Royal Society.
Michael Faraday came to believe that electricity and magnetism should be a unified concept and that light was a form of electromagnetism. But he needed the mathematics to back him up.
James Clerk Maxwell was interested in Faraday’s ideas and he had the mathematical skills to show Faraday was correct. Maxwell wanted to calculate the value of a constant “c” that he used in his equations. He built a device consisting of a pair of parallel plates and 2 coils of wire.
He gave a positive charge to one plate, a negative charge to the other and added current to them. He balanced the electric force between the plates and the magnetic force between the coils and calculated the ratio of magnetic and electrical forces to the determine the value of c. It turned out to be 300,000 kilometers per second.
Maxwell knew this matched the number James Bradley came up with a century and a half earlier. He concluded light was a form of electromagnetic waves. And he developed 4 equations that show light could be treated as a form of electromagnetic energy. His equations would later get the attention of a patent office worker named Albert Einstein.
Einstein imagined that someone on a moving boat would see waves that would appear to be in 1 place for him. But the waves would appear to be moving to an observer on land. But thanks to Maxwell’s equations Einstein knew you could not have the same experience with light waves.
Light waves from a moving vessel would appear to be moving away from any observer at the speed of light – c, (from the Latin word celeritas for “swiftness”), no matter if the observer is inside the vessel or outside the vessel.
Einstein searched for an answer to this seemingly absurd affront to common sense. Then one day he and his friend Michele Besso observed a clock. They wondered how long it take for a beam of light to reach their eyes. This was the insight Einstein was looking for.
In 1905 Albert Einstein published a paper called “On the Electrodynamics of Moving Bodies,” in the German periodical Annalen der Physik, where he introduced his “Special Theory of Relativity.” What did these words mean? It was “special” because it applied only to observers in uniform motion. “Relativity” means the only motions worth considering were the ones relative to something else.
Isaac Newton based his theory of gravity on the masses of bodies and the distances between them. He did not dwell on the matter on whether the sun was at rest or moving as the planets moved around it. Einstein believed if there was no way to determine if the sun was in a state of rest no such state could exist at all. If a swarm of people moved in a uniform motion, then each person could claim to be at rest.
Maxwell’s research made Einstein ponder yet another thing. In the nineteenth century scientists still had the mindset that electricity was electricity and magnetism was magnetism, and each domain had a set of rules that was irrelevant to the other.
But Einstein imagined a charged particle moving fast near a still magnet. In Maxwell’s world, the moving charge would speed up a magnetic force. But if the charge was not moving, yet a magnet flew by it fast the particle would speed up due to the electric force.
In both cases the particle’s acceleration would be identical!
This insight was a breakthrough in science because it showed the rules of electricity and magnetism applied equally to both disciplines because they are facets of the same thing.
If gravitational situations can not tell us what is or is not at rest, how can we expect electromagnetic situations to be any different? Albert Einstein is probably most famous for what he inferred from the absoluteness of the speed of light. Maxwell’s equations show that electromagnetic waves propagate through empty space at 300,000 kilometers per second. Einstein accepted that everybody could measure light at that speed if every observer was in uniform motion.
But as the Michelson-Morley experiment showed, the speed of light will not change no matter what kind of motion any observer is in. Einstein concluded that this could be true if 2 impossible things are possible:
1) Time does not flow at the same rate for those who are not in uniform
motion with everything else.
2) The rulers of people not in uniform motion will not be the same length
of those who are.
Thus an astronaut traveling close to the speed of light will have his ship’s clock tick slower than observers at rest outside the craft and the length of his spaceship will appear to shrink to the observers.
Einstein’s solution forces us to accept these 2 principles:
1)There is no such thing as absolute space.
2) There is no such thing as absolute time.
By rejecting absolute space, the concepts of length, height and width are relative. By rejecting absolute time, he says time is relative.
What signs do we have that Einstein was correct? One of the earliest clues came in 1937 with the discovery of muons, which are unstable particles with a half life of 2 millionths of a second. Yet we find muons entering the earth’s atmosphere decaying much slower. Since they travel near the speed of light, Einstein’s conclusions offer an explanation how they can last as long as they do.
In 1971 Joe Hafele and Richard Keating put atomic clocks on an aircraft and flew them around the world. The combined speed of the earth’s rotation and the speed of the plane slowed the clocks on the plane by 59 nanoseconds relative to clocks on the ground. This was in exact agreement with what Einstein’s equations predicted.
Through the years numerous experiments, many using high speed particles, have confirmed Einstein’s assertion that time is relative is correct.
So to help us learn about what happens inside stars we have so far learned the following:
1)Matter and energy are interchangeable.
2)Nothing can exceed the speed of light through empty space and all laws governing the universe must be designed to accommodate this reality.
3)Electricity and magnetism are intertwined and this can be shown with the principles of relativity.
But what about time and space? What exactly are these things and can they be interrelated?