Gravity is a primary force of nature. It is because of gravity that when you drop something, it falls down (instead of going up). But, what does this really mean? What is gravity?
Gravity has played a big part in making the universe the way it is. Gravity is what makes pieces of matter clump together into stars, planets, and moons. Gravity is what makes the planets orbit the stars like Earth orbits our star, the Sun.
What is Gravity
Gravity is what makes the stars clump together in huge, swirling galaxies. Albert Einstein (a great physicist), who lived in the 20th century, had a new idea about gravity. He thought that gravity is what happens when space itself is curved or warped around a mass, such as a star or a planet. Thus, a star or planet would cause kind of a dip in space so that any other object that came too near would tend to fall into the dip.
There are a number of experiments that show that Einstein was right about this idea. But there are questions for which even Einstein had no answers. For example, if gravity is a force that causes all matter to be attracted to all other matter, why are atoms mostly empty space inside? (There is really hardly any actual matter in an atom!)
How are the forces that hold atoms together different from gravity? Is it possible that all the forces we see at work in nature are really different sides of the same basic force or structure? A delicately patterned fern leaf. Shell of a pearly nautilus. An exquisitely detailed flower. Could some of the same laws of nature be at work in the designs of all things in the pictures above?
These are big questions that scientists and ordinary people like us have wondered for centuries. For a long time, we haven’t known how to go about finding the answers, other than trying to work things out on paper. NASA has a special program, called Fundamental Physics to find answers to these and other mysteries of the universe.
The goal of this new program is two-fold: a) To discover and explore fundamental physical laws governing matter, space, and time. And, b.) To discover and understand the basic rules nature uses to build the complex and beautiful structures we see around us.
Over the years, scientists and engineers have developed new technologies and instruments that will help us understand nature. Now we can take these new instruments into space and do experiments where the forces of gravity are very, very small (like when the Space Shuttle or the International Space Station are orbiting Earth in “free fall”). This way, scientists can do very delicate experiments to see what single atoms do under special conditions. NASA hopes these experiments will help us understand our universe and ourselves.
Gravity and Time
We don’t know what time is. We know a lot about time, but we don’t really understand it. The past and the future make sense because you can draw it on a line. But what about the present moment? Is it a just a dot that depends on the observer and one’s subjective perspective. Even Einstein was troubled by the concept of now, the present moment.
Philosopher Rudolf Carnap writes in his Intellectual Autobiography:
Einstein said the problem of the Now worried him seriously. He explained that the experience of the Now means something special for man, something essentially different from the past and the future, but that this important difference does not and cannot occur within physics. That this experience cannot be grasped by science seemed to him a matter of painful but inevitable resignation. So he concluded “that there is something essential about the Now which is just outside the realm of science.”