What path do photons take at sunset that allows the bottom of clouds to be illuminated? 3D has been asking this question in various threads and I felt it is critical to the whole sunset debate and needed it's own thread. If the Earth was flat and the Sun stayed at a constant altitude, direct sunlight would never be able to shine on the bottom of a cloud.
I've seen claims that this is due to perspective, but perspective can't cause this as it does not rearrange the position of objects. Think of railroad tracks appearing to draw closer to one another. At no point do the tracks appear to draw together more rapidly or shift position. The rate of change in perspective is linear, not exponential. The other option is reflection, but this doesn't hold because there is a period of time as the Sun sets where the light is coming from a roughly 90 degree angle which causes shadows to be cast from clouds that hang lower than others. If the light was reflected, the shadows couldn't form at that angle.
So, how do photons originating 3000 miles up reach the underside of a cloud?
Tom has AGAIN promised to start his own thread on this and to fully explain it. We're about a month since the first promise and many days since the second...so I wouldn't hold your breath.I have a "thought experiment" that's interesting.
Suppose you had a long, rigid tube...about the same diameter as the sun appears to be at arm's length...a half inch say. If you aim it at the sun, you should see sunshine through it...right?
Suppose I make the tube longer? The light still shines down the tube. The hole at the far end does seem to get smaller and smaller the longer the tube is.
Tom is effectively claiming that because magic perspective causes parallel lines to meet at the horizon, then if the tube were long enough to reach to the horizon - then the far end of the tube would be completely blocked - so no sunlight can travel down it.
Mmmmm'K.
This would happen (according to him) anytime the tube is longer than the distance to the "vanishing point".
For me, that distance would be infinity - but for Tom, it's at the horizon distance...because...magic.
What if we make the diameter of the tube larger? Well, Tom says that railroad tracks visibly touch each other at the horizon - so I guess a tube of diameter 4' 8.5" (the standard track gauge on US railroads) would still be closed off by perspective.
But what if I make the tube diameter larger? I don't see any limit on the size it could be. Tom seems to be saying that so long as the sides of the tube are parallel - the far end will always shrink to zero because of perspective.
So can I make a tube that's a mile in diameter - and a few miles long to reach the horizon - and it would STILL look completely dark at the end?
What if I make the tube 5 miles in diameter...still dark? At this point, the diameter of the tube is greater than it's length - but STILL no light comes through it?
The problem is that Tom's "visceral feel" that train tracks meet at the horizon starts to feel "wrong" at some point.
Parallel lines that are 5 miles apart that meet literally at the horizon would angle inwards in a most bizarre way.
Fact is, Tom's magic perspective simply isn't true. Those parallel lines meet at infinity. It's easy to convince yourself that two lines that are 4' 8.5" apart meet at the horizon - but it's a MUCH harder sell to imagine a 5 mile diameter, 3 mile long cylinder doing the same thing.
Let's push the crazy thought experiment a bit further.
Let's go back to our 1/2" diameter tube...let's make it 8,000 miles long...so it actually TOUCHES the surface of the sun at one end and my eye at the other.
Theoretically, Tom would have to say that I can't see the sun through it because of perspective...but what if I make the tube 32 miles in diameter...it's now wide enough to contain the entire Flat Earth Sun....so the sun is now INSIDE the tube...and Tom would have to say that I still couldn't see it.
But where are the sun's rays going?
Suppose it's noon - and the sun is nearly overhead.
I point my tube up vertically at the sun and even though the sun is entirely INSIDE the tube - I can't see it because of perspective. This tube is 32 miles wide and the sun is completely inside of it - but SOMETHING is stopping the photons from reaching me?!?
Then I take the tube away and I CAN see the sun.
Hmmm - so how did the photons coming from the center of sun towards me - KNOW to be blocked when the tube was there? They travel in straight lines (Tom admits this) - so they don't touch the sides...they don't even come within 15 miles of the edge of this gigantic tube. Yet they are somehow hitting the sides?!? How can this be?
Doesn't make sense.
Sadly, we know Tom will now ask "How do we know this?" "Where did anyone make a tube that big?" "Can we show him the scientific paper where they made the tube and tried it?"
I predict a total failure of imagination.