And Do You Know the Time?
Any discussion of light should lead to some discussion of James Clerk Maxwell whose famous equations let us understand light as well as all electromagnetic waves. But you might not expect that light is also associated with Einstein. The revolutionary theory of the nature of light which won Albert Einstein the 1921 Nobel prize for physics went on to help remake the world. The Economist Newspaper in their January Issue included a three page article on The Liberation of Light to observe a hundred years of bright ideas. They included an interesting story about how one member (Gullstrand) of the Nobel Committee refused to award the Nobel Prize to Einstein for his theory of relativity because he thought Einstein’s work on relativity an affront to common sense (which it sort of was) and wrong (which it really wasn’t). Each year from 1918 on, the committee received more nominations for Einstein than for any other candidate. And every year Gullstrand said no.
Eventually they nominated Einstein for his first paper in 1905 on light which he called revolutionary rather than his more important theory on relativity. Gullstrand finally agreed and the 1921 Nobel Prize in Physics was awarded to Einstein. So let’s take a close look at light which provides us with so many important things from lasers to MRIs.
Light: Light is of interest to us and most of us believe we understand light. However light is a very interesting phenomenon and has characteristics of which we may not be aware. One interesting characteristics is the fact it can behave as both a wave and a particle. Perhaps some of you have actually done the Young Experiment in high school physics or early college classes in which light is passed through slits to demonstrate its wave characteristic and most of you are familiar with TV screens which produce patterns based on light particles impacting the screen. Light can behave both as a particle and a wave. How can this be? Perhaps Einstein can help here. Many people, even those who are not scientists, are usually familiar with his famous formula E = mc2 which expresses the relationship between energy and mass. C in the equation represents the speed of light. Light is a source of energy and many are familiar with how solar panels can be converted into electric energy. Hence light can be (E) and this remarkable equation which states that energy (electromagnetic wave) can be changed into mass (m) and a particle has mass. Another remarkable thing about light is that the speed of light (c) is always constant and is the highest speed attainable in our universe. Einstein further predicted in his theory of relativity that the faster one travels relative to another object the slower time flows for the traveler relative to the flow of time measured by the stationary observer! Now that may take some “time” to sink in because it states that when we reach the speed of light, time ceases to flow altogether!
While you are taking in that important fact, let’s take another look at light using Maxwell’s equations.
Maxwell’s Equations: Since light is such an important part of this discussion I would like to include some insight to Maxwell who developed equations which enabled us to understand light as well as all electromagnetic waves. Maxwell, like Einstein, was a genius and developed a set of equations that explained mathematical everything about electromagnetic waves, including light; they were expressed in vector calculus and are as follows:
I will not attempt to explain any of the equations but I included them because some clever Electrical Engineering students decided to combine Maxwell’s equations with a Biblical verse and printed on tee shirts the following
And God Said
And there was Light!
These clever engineers certainly connected science and mathematics with religion on their T-Shirts! The equations were, of course, Maxwell’s famous equations which explained how light and other electromagnetic waves behaved. Maxwell was definitely in the class of genius and helped us to understand how the world (and universe) worked. We earlier said that time ceases to exist at the speed of light. So let’s take a closer look at time.
Time: The relationship of time and the wavelength of light was also predicted by Einstein’s theory of relativity. That theory has been proven and is now known as the law of relativity. The law of relativity tells us that the flow of time at a location with high gravity or high velocity is actually slower than at another location with lower gravity or lower velocity. The difference of time’s passage is known as time dilation. This is also a concept that is hard to grasp and we will return to the effect of gravity on time later. Schroeder notes that the clock of the universe is the light of the universe. We have heard of light years as a measure distance by calculating the time it takes for light to travel from one point in the universe to another. The need to use light years as a measure means we have a very large universe and scientists have discovered that it is continuously expanding!
Schroeder uses an interesting example to discuss the difference of time depending on your location and your speed. It involves the discovery of supernova 1987A. On the night of February 2, 1987, Ina Shelton and his assistant at an observatory in Chile were developing the last photograph of stars in the Large Megellanic Cloud. The photograph revealed a large spot not present before. It was so large they realized it could be seen by the naked eye and they went outside and could see it. What they were witnessing was the explosion of a distant star. They were familiar with the star that exploded and knew it was located some 170,000 light years away. This means that 150,000 years ago when Cro-Magnon creatures where roaming the earth, the event had occurred 20,000 years before but no one knew it. In fact, during all the history that happened since then, no one knew of the event until February 23, 1987. The question was raised, if you could have been traveling with the light wave resulting from the exploding star, how long would the trip take? The answer would be mind boggling; the answer is that no time would have passed. Since, as stated earlier, if you travel at the speed of light – time stands still! By now you may be totally confused by these scientific facts; hopefully you are also fascinated by these facts.
If that fact is not amazing enough for you then think about the other fact proven in Einstein’s theory, that gravity affects time! We know that gravity affects the weight of our mass, For example we know that our mass does not change but that on the moon, which has less gravity than the earth, we would weigh much less. To prove the point that gravity affects time let’s discuss a subject with which most of you are familiar, the GPS. The Global Positioning Satellite (GPS) system was developed during the 1960s and consisted of orbiting transmitters with precision quartz and later cesium based atomic clocks. Three of the satellites (orbiting transmitters) were used to fix the receivers position and a fourth satellite was required to set the time. Because the satellites were orbiting at 11,000 miles in space they were in a lower gravity field which the law of relativity predicted would cause the clocks to run slow by 45 milliseconds per day and because they traveled at the speed of 12,500 miles per hour it would cause the clocks to run fast by 7 milliseconds per day or a total of 38 milliseconds per day slower that clocks on earth. Software had to be programmed into the system to account for this time dilation. However because the new cesium clocks were so accurate, the software engineers blocked the relativity software when they were launched. However when the signal came down, running fast over the first twenty-four hours almost precisely by the predicted 38 milliseconds. After twenty days of gains the system was close to exceeding its allowable error and the relativity software was turned on, correcting the problem. So as you can see the laws of relativity and the effect of gravity and speed on time are real have been proven in many ways.
So we have presented some interesting (actually more than interesting) facts. Could you use them to win some bets with your drinking buddies? You can but it helps if you drink with nerds. So here are a few questions that may win you a beer or two.
- What did Einstein win the 1922 Nobel Prize for Physics? (most would say relativity but it was for the theory of light)
- If you were 3 million light years away and were traveling on a light wave how long would it take you to get to earth? Zero time because at the speed of light time stands still (hope you have good persuasion skills).
- What is the fastest speed you can attain on earth? The speed of light!
BUT WAIT!
The last answer may be wrong. Quantum entanglement now says pairs can have interaction at speeds greater than the speed of light! Can that be true. Well let’s take a brief look at what quantum entanglement is:
Quantum entanglement is a physical phenomenon that occurs when a pair or group of particles is generated, interact, or share spatial proximity in a way such that the quantum state of each particle of the pair or group cannot be described independently of the state of the others, including when the particles are separated by a large distance. The topic of quantum entanglement is at the heart of the disparity between classical and quantum physics: entanglement is a primary feature of quantum mechanics lacking in classical mechanics. This means that interpretations of entanglement could prove that the transmission at faster-than-light is possible. This is very controversial and as more quantum entanglement can demonstrated experimentally perhaps they will prove that transmission at faster-than-light is possible.
What does this mean? For one thing it would mean that the answer to question 3 could be wrong. And believers in the fact that the speed of light is the fastest possible, like me, will have to be open to changing their view of this bit of new scientific fact. And I hope that I will be more open to this new confusing (and hard to believe) quantum physics than was Gullstrand (who was also confused by Einstein’s relativity theory.)
Well as we come to the end of this blog I probably do not have to remind you that I introduced you to some very strange scientific facts and some complex ideas like quantum entanglement and some complex mathematics like Maxwell’s equations. I have tried to “lighten” up (pun intended) the discussion to hopefully also amuse you with the suggestions you could use this information to win a few beers. But this whole blog gives a perfect example why we should never consider that the science is complete and no more debate is needed. We learn with our willingness to question how things are done. Particularly in science and mathematics, great minds have been able to add to our knowledge through new concepts that only they could understand and develop. Fortunately for us science and mathematics seem to be open ended when it comes to new theories and concepts. Keep an open mind, never doubt that there may be a better solution. Beware of people that push the idea that there is no need for further debate, the science is complete. History continually shows us that that is not true.
This blog has been fun for me ( I guess you have figured out that I am a nerd at heart).
Will Lannes