Name: Why the Sky ISN'T Blue
Uploaded: 2020-03-28T18:22:49.000Z
Duration: 7 min 53 s
Description: Thousands of YouTube videos with English-Chinese subtitles! Now you can learn to understand native speakers, expand your vocabulary, and improve your pronunciation...

Thank you guys so much for subscribing to my channel and for joining me on this scientific

You know, if you got 500,000 people together and we all held hands in a line, it would

stretch from Sydney to Melbourne or from San Francisco to San Diego or from London to Inverness.

So I suppose I should get down to answering your question.

>> I understand that the sky is blue do to Rayleigh scattering.

Short wave lengths get scattered way more and blue light dominates because it is so

If that is the case, why isn’t the sky violet?

So the sky is illuminated by the sun and the sun in its all colors, but not equally.

The sun doesn’t emit that much red, nor does it emit that much violet.

Most of the light it emits is kind of in the greeny part of the spectrum.

Now as you point out, due to Rayleigh scattering more of the shorter wavelengths arte scattered

and that is why the sky looks blue, because it is basically the sun’s white spectrum

And, in fact, there is a fair amount of violet light in there.

But there is not as much violet light as there is blue light, because the sunlight that we

started with had much more blue than it has violet.

>> If I have a lap top on the international space station with a hard disk drive in it,

will the torque from its spinning cause the lap top to spin as well?>>

Well, by the law of conservation of angular momentum, yes, the lap top should spin.

I did a quick back of the envelope calculation and I found that if you spun up your hard

disk from rest up to 5400 rpm, then it would cause the laptop to spin in the opposite direction

at a rate hat would cause it to do about one revolution every 17 seconds.

>> What would happen if you poured liquid oxygen on a fire?

>> Say you were able to pass the event horizon a black hole and come back, what would coming

back look like of the person and for an observer?

>> Well, to an outside observer it would look as though you never came back at all.

And to the person it would look as though you didn’t come back either, because once

you are passed the event horizon, that is it.

Your entire future lies within the black hole.

And it will only be a matter of seconds before you are in the singularity, the very core

of this black hole and you are no longer.

Now if you could bring a rocket back with you and try to fight it, if you tried to accelerate

away from the black hole, you would find that you actually live for less time.

You might see more space, but your time would pass more slowly and so you would end up in

So I guess the lesson is don’t fight it.

If you want to live longer, just relax and go with it.

>> You have met a lot of interesting people on your adventures.

But is there someone specific that you would love to meet?

>> I would love to meet Bill Nye, Neil DeGrasse Tyson, Richard Dawkins and President Obama

So if you haven’t read The Audacity of Hope that is a good recommendation.

>> If all the galaxies are constantly accelerating away from each other, will they ever reach

the speed of light or stop accelerating all together?

>> So, yeah, all the galaxies do seem to be accelerating away from each other, faster

and faster, which makes this kind of a unique time in the history of the earth, because

right now we can still see that there are hundreds of billions of galaxies.

But sometime in the future due to the expansion of the universe, those galaxies will be so

far away and, yes, they will be receding at faster than light speed and then you might

say: Well, nothing can go faster than light.

And it is kind of true in that these galaxies won’t be moving through space at a speed

faster than light, but the space in between us and them will be expanding at a rate which

means they will be moving relative to us faster than light, if that makes any sense.

So their light that they are emitting will never be able to reach us, because it will

never be able to make progress through this expanding space.

It is kind of interesting to think about what will happen as that time approaches.

Well, the light that is coming from those distant galaxies travels across this expanding

And so it becomes red shifted, cosmologically.

And eventually the wave length of this light will be so big that its wavelength is the

size of the whole universe and that is impossible to detect.

So at some point, probably about two trillion years in the future we will only see our local

Now the reason they haven’t gone out to infinity, or very, very far away is because

So even though space is expanding on a large scale, the gravitational force is enough to

hold all of us together so we will be in it for the long haul.

But this still means that there is going to be strange cosmology.

If we are still around trillions of years from now, if we tried to look out, we would

see a very different universe, a universe which is much emptier than the one we see

So we live at a unique point in space time.

>> Is there such a thing as randomness in the universe?

And if so, isn’t that contradictory to science?

>> Yes, I think there is randomness in the universe and, no, I do not think this contradicts

Though, perhaps you are thinking along the lines of Albert Einstein when he said: God

He wasn’t happen when in quantum mechanics it seemed as though some events have probabilistic

I mean, he thought that there were some hidden variables there and we just didn’t know

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Why the Sky ISN'T Blue

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