It's perfectly obvious the time has a direction
All we mean by that is that the past is different from the future in lots of different ways
We were younger in the past, we will be older in the future
We remember the past, we don't remember the future
The surprise is that that difference between past and future
is nowhere to be found in the deep down laws of physics
Time is actually a lot like space if you're out in a space suit flying around
there will be no difference between up, down, left, right
likewise, there is no intrinsic difference between the past and the future
in the laws of physics. Now that's not completely a mystery to us
we know that what actually happens in the real world
is that you're not just made of one or two particles
bumping into each other, you're a very very complicated collection
of many many particles and they're becoming more disorderly with time.
this is just saying that entropy increases.
The interesting thing is that every difference between the past and the future
will utimately be traced to the fact that the entropy was lower
in the past and is growing. That's the Second Law of Thermodynamics
The universe was orderly, it's becoming more disorderly
That's not a surprise. There is more ways to be disorderly than to be orderly.
The suprise is that the universe was ever low entropy to begin with.
If we go all the way back to the Big Bang, 13.7 billion years ago, the universe began
in a highly ordered state. So, modern cosmologists are trying to understand
right now why the early universe was in a such precise state.
why it was so low entropy. Once we understand that,
it will make perfect sense to us why the arrow of time stretches
as it does from the past to today all the way toward the future.