Brian Cox explains why time travels in one direction - BBC

Professor Brian Cox builds sandcastles in the Namib Desert to explain why time travels in one direction. It is a result of a phenomenon called entropy; a law of physics that tells us any system tends towards disorder.

#bbc #bbciplayer

[JoeC-]

I remember watching this as a child when it was first aired and the ideas made a lasting impact. Now I’m about to take on a PhD related to entropy and complex systems. Epic and memorable scene!

[benschuster]

"I'm going to create some order in the universe" *colonises the desert*

[verdaderoken]

You can tell Brian Cox is very passionate about what he says and tries to explain it as easy as possible for the audience. much respect for this guy

[Jake-vhjp]

Prof Brian Cox is the David Attenborough of Space and Time. Both national treasures

[Dempy]

I love the way he talks, so gentle and happy

[_rlb]

First law of Youtube dynamics: every video will be in your recommended list after ten years.

[lotusmanb]

I can listen to Dr Cox all day with the enthusiasm of a child in his voice. He makes it easier to understand imo. Thank you

[oldcaptainjack]

I was about 22 when I first saw this on TV when it came out and it stuck with me ever since. Saw Brian Cox live 2 years ago on his tour, he's one of those interesting people you could listen to speak about theories of things for hours, literally. I especially love how he makes it 'accessible' and keeps explanations simple for everyone to keep up.

[floyd_fanatic]

I know this is late but this man is absolutely a gem. I've been watching his documentaries all throughout the years and he explains science in such beautiful and poetic ways it just sends a shiver down your spine. People like these are the ones who ignite the spark of curiosity in a child's mind who in turn grows up to do even greater things in life.
Hats off to such guys.

[Gavinlovesfishing]

Legend has it that Brian Cox has never shouted in his entire could be telling me my entire family have been wiped out and that voice would sooth away my grief!

[andraspongracz]

Imagine you are shown video footage of the wind turning the sand castle into a pile of sand. Now imagine it is played backward. The reverse footage shows a pile of sand spontaneously turning into a castle. You would know immediately that the first video is real and the second one is played backward, not the other way around. It is normal for complex things to disintegrate, but not for complex things to appear out of thin air. That's how you can tell which way time goes. It is also this exact law that contradicts time travel back to the past. (Funnily enough, it is consistent with time travel into the future.)

[davidschmidt]

Never saw this before, although I did ALWAYS use another video of his in my classes covering acceleration, atmospheric resistance and terminal velocity. In it, he drops a bunch of feathers and a bowling ball simultaneously, from being suspended perhaps 20 or so meters in the air inside the world's largest vacuum chamber. They, of course, hit the ground at the exact same time. Great to watch!!
This is a novel and utterly (IMHO) perfect way to explain time's flow. Never have I seen anyone better define such an abstract as 'time' by explaining its simple adherance to the laws of Physics, and specifically Thermodynamics. It also proves the only other decent explanation for time I'd ever seen....that " Time is a measurement of change."
VERY well done, and Thank you, Professor Cox.

[kukualoo]

"You cant reverse time, trust me" - The man who gets younger with age

[Jackmerius_Tacktheritrix]

More fascinating than entropy and time travel is how he managed to not get any sand in his eye

[mayanksingh]

This is the most amazing way of understanding laws of thermodynamics and concepts of entropy

[stargazerAPRL]

Wonders of the universe, my favourite tv show ever, I never missed an episode of it . Thanks professor brian cox for igniting my interest in space .

[alexboniface]

This guy Brian Cox is an absolute legend, everything he's done with his life is amazing, massive respect to him and all the efforts he's put in to being able to do what he loves

[zachnies]

For anybody confused about the question in the title: Entropy goes from low to high with the passage of time because of the 2nd law of thermodynamics. This works well if time travels in 1 direction. If time traveled in the opposite direction, you should expect the opposite trend which is high to low entropy. This isn't the case (as far we know), therefore time travels in 1 direction.

[pcbacklash_]

I've long heard the entropy explanation for why time only appears to move in one direction, but I often wonder if we haven't been looking at time altogether incorrectly.

We always seem to treat it as some mathematical abstraction, or some linear line of events, tacked on at the last minute to our understanding of the physical universe. But I've pondered the notion that perhaps time is actually _cumulative_ -- that it doesn't move or travel so much as it merely continues to add to itself, like an ever-expanding sphere.

I don't have the physics knowledge to be able to actualize this idea, but I know that time is already recognized as integral to the composition of space (space-time). I simply suspect it has more of a 'physical' presence than is currently believed. If so, it _could_ help explain the ever-increasing rate of expansion of the universe, what we now attribute to "dark energy" (which NOBODY understands).

[jred]

Brian has such a unique way of explaining these things.