Emergence of Modern Science

1. Emergence of Modern Science NS 1300 Dr. Hoge

2. Traveling at the Speed of Light • Can we slow light down? • Can we make things invisible? • Is it possible to travel faster than the speed of light? • Is faster than light communication possible? • Worm holes?

3. Relativity • Frames of Reference • Science makes two grand assumptions: • Every observer must experience the same laws (that is to say that the laws of physics are the same throughout the universe). • The laws of the universe are constant with time. • Everything Is Relative

4. Relativity • Special Relativity • Distance and time are not absolute • All uniform motion is relative • There is no absolute state of rest • General Relativity • A geometric theory of gravity • Equivalence principle: gravity is equivalent to acceleration • Mass warps space-time • Gravity is the acceleration of masses due to these warps in space-time

5. The Significance of Relativity • The principle of relativity, which states that there is no stationary reference frame, dates back to Galileo, and was incorporated into Newtonian Physics. (Remember the bucket problem) From Wikipedia

6. The Aether • However, in the late 19th century, the existence of electromagnetic waves led physicists to suggest that the universe was filled with a substance known as "aether", which would act as the medium through which these waves, or vibrations traveled.

7. Wherefore art thou aether? • The aether was thought to constitute an absolute reference frame against which speeds could be measured. In other words, the aether was the only fixed or motionless thing in the universe. • Aether supposedly had some wonderful properties: it was sufficiently elastic that it could support electromagnetic waves, and those waves could interact with matter, yet it offered no resistance to bodies passing through it.

8. Einstein to the Rescue • The results of various experiments, including the Michelson-Morley experiment, indicated that the Earth was always 'stationary' relative to the aether — something that was difficult to explain, since the Earth is in orbit around the Sun. • Einstein's elegant solution was to discard the notion of an aether and an absolute state of rest.

9. Relativity • Special relativity is formulated so as to not assume that any particular frame of reference is special; rather, in relativity, any reference frame moving with uniform motion will observe the same laws of physics. • In particular, the speed of light in a vacuum is always measured to be c, even when measured by multiple systems that are moving at different (but constant) velocities. c = 299,792,458 m/s

10. Special Relativity – What a Concept • Time Dilation • Distance Compression • Mass Expansion

11. General Relativity • Newton’s Gravity = G = M1XM2/d2 • Einstein’s Gravity = The curvature of space-time

12. Space-time • Time and distance are the same dimension. • Gravity is the acceleration of space-time

13. Gravity and Light • Gravitational bending of light • Gravitational lenses • Discovering new planets

14. Quiz • 1. T or F, everything is relative. • 2. T or F, Einstein developed the theory of special relativity but not general relativity. • 3. T or F, special relativity states that time slows down as you approach the speed of light. • 4. T or F, we can explain gravity. • 5. T or F, general relativity describes gravity as the acceleration of space-time.