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A Lesson in EinsteinDaniel Johnson Salem-News.com
"For those of us who believe in physics, this separation between past, present and future is only an illusion, however tenacious" - Albert Einstein
(CALGARY, Alberta) - It started for me in the 1950s with a TV commercial for Kellogg’s Corn Flakes. The animated commercial showed a sunbeam zipping from the Sun to an ear of corn in a field. The voiceover said that it takes eight minutes for the Sun’s goodness to reach the corn in the field.
It’s basic arithmetic. The Sun is an average of 93 million miles away; the speed of light is 186,000 miles per second. Divide 93 million by 186,000 and the answer is 500 seconds, or eight and a third minutes.
I didn’t get it right away but when I was about 13 I became seriously interested in amateur astronomy. I got a pair of binoculars and went out most nights (even in the winter) and looked at the moon and the stars.
One of the things I learned is that the stars are suns and, to appear so small, they were a tremendous distance away. Astronomers use the term light-year (ly) to define distance. The brightest star in the sky is Sirius, also known as the Dog Star, visible through the winter in the southern sky. It’s 8.6 ly away. A light year is a distance—how far a photon of light travels in a year. I’m not going to write out all the zeros, but a ly is about 5.9 trillion miles which makes Sirius about 50 trillion miles away.
This is where it came together for me. When looking at Sirius, I realized that I was looking at the star as it was 8.6 years ago, not as it is now. The Kellogg’s commercial made its mark. If the Sun were to explode as a nova, we would not know about it until 8.3 minutes after it happened. This is where the concept of what now is came to me.
Looking at the Sun, it is in our past, but even more startling we are in the Sun’s future. I looked out at the Andromeda Galaxy which is now estimated to be two million light years away and understood that when the light from Andromeda set out on its way to us, Homo Sapiens hadn’t even appeared on the earth yet. But more to the point. Our now is two million years in Andromeda’s future.
Enter Albert Einstein
On hearing of the death of his lifelong friend Michel Besso, Einstein wrote to Vero and Bice Besso on March 21, 1955, saying: “So in quitting this strange world he has once again preceded me by a little. That doesn’t mean anything. For those of us who believe in physics, this separation between past, present and future is only an illusion, however tenacious.
Now is a meaningless concept to physicists because it cannot be defined within physics. Says physicist Brian Greene: “There are no known physical mechanisms that singles out moment after moment to be momentarily real, to be the momentary now.” Just as there is no fixed place in the universe, so there is no fixed now in the universe.
Einstein’s best friend, logician Kurt Gödel questioned whether time exists at all: “The existence of an objective lapse of time means that reality consists of an infinity of layers of ‘now’ which come into existence successively. But if simultaneity is something relative, each observer has his own set of ‘nows’ and none of these various layers can claim the prerogative of representing the objective lapse of time.”
Einstein came to his theory of relativity through trying to resolve the puzzle of simultaneity, that is, how do we know that two events happen at the same time or are simultaneous? His answer, the Special Theory of Relativity, showed that there is no absolute time against which events can be compared. Consequently, there is no now that can be defined except through personal experience.
The simplest demonstration of Einstein's original idea is found in our GPS system. GPS devices could not work if it weren't for the application of both of Einstein's theories--General and Special Relativity. Time flows at different rates depending on the relative speeds between two locations (special relativity) and flows at different rates according to the gravitational field. (general relativity) A satellite is in a weaker gravitational field compared to us on the surface of the earth, so time for an orbiting satellite flows slower compared to us. The difference is small, but measurable. If the two theories were not used, the GPS earth position would be off by ten kilometers after just one day and become farther and farther off every day.
Astronomer Donald Goldsmith once calculated that the men who spent 84 days in orbit in Skylab, moving at a speed relative to ourselves of about 8 km/sec aged about 1/5000 of a second less than those who stayed on earth.
On the surface of the earth we are all in essentially the same gravitational field, so our nows are very close, but not identical. Think of airline pilots. They regularly experience both speed and a reduced gravitational field. Or people who drive for a living, like long distance truckers, railway engineers and bus drivers. Their experience of speed, overall, is much greater than that of a deskbound worker. The technology does not exist to actually measure that they are in a different now compared to a sedentary person, but no physicist doubts it.
We can go one step further. Think of yourself briskly walking down the street swinging your arms with abandon. Your torso is moving at a fixed rate, but your arms are moving faster. Although the time differences are technologically undetectable, our arms and legs are younger by trillionths of trillionths of seconds. Although the differences are extremely small, they show a fundamental flaw in our commonly held conception of universal space and time.
So, it turns out that even our bodies are not the physically unitary constructions we believe them to be. And Alice thought her world was strange.
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