The Day We Found the Universe - Marcia Bartusiak [74]
This was not the iconic Einstein—the sockless, rumpled character with baggy sweater and fright-wig coiffure—but a younger, more romantic figure with alluring brown eyes and wavy dark hair. While in his twenties and thirties, he was at the height of his prowess. Among his gifts was a powerful physical instinct, almost a sixth sense for knowing how nature should work. This often involved his thinking in images, such as one that began haunting him as a teenager: If a man could keep pace with a beam of light, what would he see? Would he see the electromagnetic wave frozen in place like some glacial swell, as Newton's laws were suggesting? “It does not seem that something like that can exist!” Einstein later recalled thinking.
After pondering this issue long and hard, Einstein came to realize in 1905 that since all the laws of physics remain the same—whether you're at rest or in steady motion, sitting quietly on a beach or reading on a train—then the speed of light has to stay constant as well in both situations. He had found the answer to his question. No one can catch up with a light beam, no matter how fast they are traveling. Whether your feet are firmly planted on Earth or aboard a spacecraft speeding toward a far planet, you'd measure the exact same pace to light's motion, 299,792 kilometers (186,282 miles) per second.
How is that possible? It seems to go against common sense. But Einstein ingeniously deduced that if the speed of light is identical for all observers, no matter what their state of motion, then something else has to give. And that something else was absolute time and space. With his special theory of relativity, Einstein completely altered the traditional perspective of classical physics that had been firmly established by his illustrious predecessor. “Newton, forgive me,” said Einstein in his autobiographical notes. “You found the only way which, in your age, was just about possible for a man of highest thought—and creative power.” In Newton's world, there was one universal clock and common reference frame, which made time and space the same for one and all throughout the cosmos. But that scheme no longer held. Instead, space and time were now “relative,” flowing differently for each one of us depending on our motion. Einstein intuited that length and time are adjustable. If two observers are uniformly speeding either toward or away from each other, each will measure space shrinking and time proceeding slower for the other. Their clocks and yardsticks will not match up, as they did under Newton's laws. The only thing that they will agree on is the speed of light, a universal constant that remains unchanged for both travelers. The reason this seems counterintuitive is that we can't readily discern these differences in length and time in our rather humdrum surroundings. The changes are only apparent when the speeds between two objects are enormous, a sizable fraction of the velocity of light.
Soon Einstein was not satisfied with that adjustment alone. Special relativity was just that—special. It could only explain the properties of objects moving at an unvarying velocity. But that restricted its use to a great extent. Most events in nature don't behave so methodically. What if something were speeding up, slowing down, or changing direction? What if an object were accelerating under the force of gravity? Einstein knew that he had to develop a more