Just like everybody, time travel fascinates me too! So, whatever I do, I try to link it up to time travel! And sometime ago, I’s studyin about the Doppler’s effect in sound waves, and an argument kept buggin me. [The below discussion’s not just confined to sound, obviously!]
When we approach a stationary source, from, Doppler’s law, we can deduce, the frequency does increase. But, this would also mean that the number of disturbances [caused by the waves], that we pass in an unit time is increased too.
So we’d hear the sound, somethin like, when it’s fast forwarded.
And, when we move away from the source, faster than the speed of sound[in that medium], it’d be like, we rewind the disk and play it again (I know i’m bad at analogy, but this should do it). Like, you hear it once. Speed through the medium[without disturbing the original sound wave], reaching some point it’d reach, before it does. Then, we’d hear it again!
Now, what exactly we associate time with is, the events and their order of taking place. Like, the most common example, a cup falling off a table onto an uncushioned floor and it breakin. We’ve never witnessed its opposite. The thermodynamics state that the net entropy change of the universe can never be negative. So, the cup stickin back together is practically impossible when left for itself. If we do find some way to stick it back, then the net entropy change of the universe is again positive.
But what I think is, there’s one way to witness the whole event yet again. Yeah, this’s where the Doppler’s discussion comes in. It’s just like when you’re lookin at a star, a million light years away, we’re lookin into its history. We’ll never know if the star is still active at the moment we’re lookin, till we find a way to propel ourselves to the speeds of light. One thing which puts us on hold is this strange behaviour of light. Experiments show speed of light is not a constant. For instance, if for you(assumin that you’re on earth, stationary with respect to it), the speed of light is “c”, then for someone, who’s on a moving spaceship, the speed would still be “c” alone. So, this makes backward travel of time impossible for now.
But, the forward travel would still be possible since it’s not a compulsion to travel in the speeds of the range of light. Even a fraction would just do fine.(which is pretty difficult too!)
David Thorne narrates one of his childhood experiences!
” When I was about twelve, I read
that time slows down when
approaching the speed of light
so I constructed a time machine
by securing my father’s portable
generator to the back of my
mini-bike with rope and
attaching the drive belt to the
back wheel. Unfortunately,
instead of traveling through time
and finding myself in the future,
I traveled about fifty metres
along the footpath at 200mph
before finding myself in a bush.
When asked by the nurse filling
out the hospital accident report
“Cause of accident?” I stated
‘time travel attempt’ but she
wrote down ‘stupidity’. “