Time Travel in Einstein's Universe: The Physical Possibilities of Travel Through Time
J. Richard Gott
Language: English
Pages: 304
ISBN: 0618257357
Format: PDF / Kindle (mobi) / ePub
Ciclos del tiempo: Una extraordinaria nueva visión del universo
The Dancing Wu Li Masters: An Overview of the New Physics
Sun in a Bottle: The Strange History of Fusion and the Science of Wishful Thinking
Planet Formation: Theory, Observations, and Experiments (Cambridge Astrobiology)
foot. He w o u l d see t h e m TIME TRAVEL TO THE FUTURE oscillate once every fourth of a n a n o s e c o n d as they went b y h i m rather than the once-a-nanosecond oscillation they had w h e n they were emitted. T h e time traveler w o u l d thus observe the distant observers' clocks to be ticking 4 times too fast. T h e time traveler w o u l d see the history of the outside universe passing i n front of his eyes at 4 times the n o r m a l rate. It w o u l d resemble a m o v i e playing at
around. A supernova flaring up i n a distant galaxy can make the evening n e w s today, w h e n its light reaches us, e v e n though the event h a p p e n e d v e r y long ago. But you might also like to see past events o n Earth. E v e n that is possible. Do y o u w a n t to see yourself i n the past? S t a n d 5 feet i n front of a mirror. T h e image y o u see of yourself is not of y o u n o w but of y o u 10 nanoseconds ago. Traveling at 1 foot per nanosecond, light takes 5 nanoseconds to go
example, a flat sheet o f paper obeys the tenets of E u c l i d e a n geometry, but y o u can roll it u p a n d tape the left a n d right edges together to create a cylinder. If y o u were a Flatlander living o n such a cylinder, you might think you were still living o n a flat plane because triangles w o u l d still have a s u m of angles that is TIME TRAVEL IN EINSTEIN'S UNIVERSE 180 degrees. But if you walked around the cylinder's circumference, without changing direction, you w o u l d
the whole universe was e x p a n d i n g — o n e of science's greatest results a n d biggest surprises. T h u s E i n s t e i n ' s universe model included a prediction that was proved false. I n E i n s t e i n ' s model, galaxies w o u l d forever r e m a i n at the same distance f r o m o n e a n o t h e r — t h e y w o u l d not be m o v i n g apart. M e a n w h i l e , A l e x a n d e r F r i e d m a n n h a d already found the answer. H e solved Einstein's original equations e x a c t l y —
d have a finite chance to tunnel (becoming a four-dimensional space w i t h n o t i m e — t h e black region i n Figure 26) a n d emerge o n the other side as a n e x p a n d i n g de Sitter spacetime. I f it failed to tunnel, it w o u l d just roll back d o w n to the bottom of the valley a n d continue oscillating there. E a c h oscillation gives it a chance to tunnel out, so eventually it w o u l d . I n Figure 26 the t u n n e l i n g (in black) connects two ordinary spacetimes (both
