4.16 Einstein’s Concept of Gravity
Einstein Explained It All
In the early 1900s, Albert Einstein came up with a theory of gravity that actually explains gravity rather than simply
describing its effects. Einstein showed mathematically that gravity is not really a force that of attraction between all
objects with mass, as Newton thought. Instead, Einstein showed that gravity is a result of the warping, or curving,
of space and time, which made up the same space-time “fabric.” These ideas about space-time and gravity became
known as Einstein’s theory of general relativity. If you watch the video at the URL below, you can see how Einstein
developed his theory. The video may also help you understand how Einstein’s theory differs from Newton’s law.
http://www.youtube.com/watch?v=O-p8yZYxNGc
Visualizing Einstein’s Ideas
Einstein derived his theory using mathematics. However, you can get a good grasp of it with the help of a simple
visual analogy. Imagine a bowling ball pressing down on a trampoline. The surface of the trampoline would curve
downward instead of being flat. Now imagine placing a lighter ball at the edge of the trampoline. What will happen?
It will roll down toward the bowling ball. This apparent attraction to the bowling ball occurs because the trampoline
curves downward, not because the two balls are actually attracted to one another by an invisible force called gravity.
Einstein theorized that the sun and other very massive bodies affect space and time around them in a way that
is similar to the effect of the bowling ball on the trampoline. The more massive a body is, the more it causes
space-time to curve. This idea is represented by theFigure4.30. According to Einstein, objects move toward one
another because of the curves in space-time, not because they are pulling on each other with a force of attraction.
Einstein’s theory is supported by evidence and widely accepted today, although Newton’s law is still used for many
calculations. You can see an animation of the warping of space-time at the following URL.
http://einstein.stanford.edu/Media/Einsteins_Universe_Anima-Flash.html
For a live video demonstration, go to this URL: http://www.youtube.com/watch?v=uwtJaQyXpQs.
MEDIA
Click image to the left for use the URL below.
URL: http://www.ck12.org/flx/render/embeddedobject/82423To learn about some of the evidence in support of Einstein’s theory, go to this URL:
http://www.universetoday.com/85401/gravity-probe-b-confirms-two-of-einsteins-space-time-theories/
Summary
- Newton’s law of gravity can predict the motion of most but not all objects. It also doesn’t explain gravity. It
only describes its effects on the motion of objects. - Einstein showed mathematically that gravity is not really a force of attraction between all objects with mass,
as Newton thought. Instead, gravity is a result of the warping of space-time. - Einstein’s ideas have been supported by evidence and are widely accepted today.
Vocabulary
- gravity: As traditionally defined, force of attraction between things that have mass.