Why would'nt this work?
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It can look dumb, but I always had this question as a kid, what physical principles would prevent this?
There's a bunch of these thought experiments that try to posit scenarios where C is violated.
Here's one I remember from uni involving scissors. Similar to what OP was thinking, but really really big scissors.
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It can look dumb, but I always had this question as a kid, what physical principles would prevent this?
Long winded video about it:
'Are solid objects really โsolidโ?' (go-to 7:30)
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The problem is that when you push an object, the push happens at the speed of sound in that object. It's very fast but not anywhere near the speed of light. If you tapped one end of the stick, you would hear it on the moon after the wave had traveled the distance.
I swear I've seen a video of someone timing the speed of pushing a very long pole to prove this very thing. If I can find it I'll post it here.
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Damn, so that means no FTL communication for now...
Hear me out... What about a metal stick?
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The problem is that when you push an object, the push happens at the speed of sound in that object. It's very fast but not anywhere near the speed of light. If you tapped one end of the stick, you would hear it on the moon after the wave had traveled the distance.
I assume the post is saying that theyโre both touching the ends of the stick and then one person pushes. It would be instant. What would sound have to do with an object moving? Purely mechanical communication.
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Damn, so that means no FTL communication for now...
Are you saying that the person on the moon would feel a tap from the other end or the person would actually push the stick forward towards the manโs hand on the moon?
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It can look dumb, but I always had this question as a kid, what physical principles would prevent this?
I'm not a scientist, but when I asked the same question before they said, "compression."
Like, the stick would absorb the power of your push, and it would shrink (across its length) before the other end moved. When the other end does finally move, it's actually the compression reaching it.
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Hear me out... What about a metal stick?
Metal is a lot heavier than wood. You'd never be able to lift it to the moon.
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It can look dumb, but I always had this question as a kid, what physical principles would prevent this?
How heavy would a stick of this size weigh?
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Metal is a lot heavier than wood. You'd never be able to lift it to the moon.
What if you had a crane?
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Metal is a lot heavier than wood. You'd never be able to lift it to the moon.
But can you lift it from the moon? Gravity is a lot lower there.
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How heavy would a stick of this size weigh?
Weigh on Earth or on Moon?
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How heavy would a stick of this size weigh?
We're supposing that you have an herculean strengh and that weight is not a problem
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But can you lift it from the moon? Gravity is a lot lower there.
Large if factual
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Do you think it would be possible if you remove the astronauts eyelids? Would that enable faster than light communication?
The only way to know for sure is by trying
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So I found a dowel rod online that's 1 meter long by 25 mm in diameter made of beech, which is pretty typical for this kind of rod. Each rod weighs 420 g. 300,000 km is 300,000,000 m. So for a dowel rod to be 300,000,000 m long, it would weigh 126,000,000,000 g, or 126,000,000 kg. You would never be able to push this rod. If you had a magical hydraulic ram that could, it would just compress the soil under it. This is on the scale of the foce released from an atomic bomb.
But let's throw that out and pretend the whole thing weighs 420 grams instead. Maybe it's made of a novel, space-age material instead of beech. And since you've said it can't bend or break, the portion at the surface of the earth would be spinning at roughly 1,000 kph (due to the rotation of the earth), and the portion at the end of the rod would be spinning at about 28 km/s. Most of the mass of the rod would be spinning faster than escape velocity, so you wouldn't be able to hold onto it. It would be gone almost instantly.
Let's pretend you could hold onto it. Then the person on the moon couldn't hold it, because the earth rotates on its axis about 28 times faster than the moon travels around its orbit. So you can see how this problem devolves into ever more layers of magic and hand-waiving.
The final problem is the fundamental difference between classroom physics and material engineering. If you could fix the moon to the end of the rod, and you used a space-age material that weighs 420 g for the whole thing, and it could be so rigid as to not bend, then it would have to break instead. If, instead, it's designed to not break, then it must be able to bend. This is just how real materials work. But even if it does neither, or at most only bends a little, it is still true that as you push on the rod it would compress. So the tip wouldn't move at first. The pressure would move through the rod like a wave. You can't send information faster than light.
Yes, about my setting, it was pretty much an excuse to illustrate the experiment, with like you said, a bit too much of magic.
The moon being on a straight distance of 1 light second, i didn't had found another place to put this experiment on. So I didn't take into account the herculean strengh needed, the movement of the earth and the moon and the gravity.
Someone gave a link to an answer of my question, with a more realistic take on the position of the other end, but your explanations are still welcome for this moon setting and the "moon elevator" problem
(i know i may have broken english sometimes, sorry about that)
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Yes, about my setting, it was pretty much an excuse to illustrate the experiment, with like you said, a bit too much of magic.
The moon being on a straight distance of 1 light second, i didn't had found another place to put this experiment on. So I didn't take into account the herculean strengh needed, the movement of the earth and the moon and the gravity.
Someone gave a link to an answer of my question, with a more realistic take on the position of the other end, but your explanations are still welcome for this moon setting and the "moon elevator" problem
(i know i may have broken english sometimes, sorry about that)
(i know i may have broken english sometimes, sorry about that)
Not at all! I couldn't tell you aren't a native speaker. Regarding a "moon elevator", or more realistically a space elevator, these kinds of Herculean physics problems are exactly what people are trying to iron out. The forces involved are astronomical.
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So I found a dowel rod online that's 1 meter long by 25 mm in diameter made of beech, which is pretty typical for this kind of rod. Each rod weighs 420 g. 300,000 km is 300,000,000 m. So for a dowel rod to be 300,000,000 m long, it would weigh 126,000,000,000 g, or 126,000,000 kg. You would never be able to push this rod. If you had a magical hydraulic ram that could, it would just compress the soil under it. This is on the scale of the foce released from an atomic bomb.
But let's throw that out and pretend the whole thing weighs 420 grams instead. Maybe it's made of a novel, space-age material instead of beech. And since you've said it can't bend or break, the portion at the surface of the earth would be spinning at roughly 1,000 kph (due to the rotation of the earth), and the portion at the end of the rod would be spinning at about 28 km/s. Most of the mass of the rod would be spinning faster than escape velocity, so you wouldn't be able to hold onto it. It would be gone almost instantly.
Let's pretend you could hold onto it. Then the person on the moon couldn't hold it, because the earth rotates on its axis about 28 times faster than the moon travels around its orbit. So you can see how this problem devolves into ever more layers of magic and hand-waiving.
The final problem is the fundamental difference between classroom physics and material engineering. If you could fix the moon to the end of the rod, and you used a space-age material that weighs 420 g for the whole thing, and it could be so rigid as to not bend, then it would have to break instead. If, instead, it's designed to not break, then it must be able to bend. This is just how real materials work. But even if it does neither, or at most only bends a little, it is still true that as you push on the rod it would compress. So the tip wouldn't move at first. The pressure would move through the rod like a wave. You can't send information faster than light.
That was excellent. Thank you
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Because the stick isn't infinitely rigid. If you push it at one end the other end doesn't immediately start moving. The time it takes, I think, is equal to the speed of sound inside that material. Ultimately the forces that bind atoms together and allow them to interact are limited by the speed of light.
Huh....so we may fail to achieve faster than light (FTL) travel but we could probably manage faster than stick (FTS) travel
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What if you had a crane?
Or a duck.
