Science questions not worth a thread I: I'm a moron!

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Hey guys, I have a question.

Say that you're standing 1 lightyear from a button that you want to press. Now, say that there's a wooden plank 1 lightyear long extending from you to the button, almost, but not quite touching it.

Now, I know that pressure waves travel at the speed of sound through a material (so if you pushed the plank into the button, it would take some thousands of years to reach the button).

But what if you accelerated the plank of wood instantaneously from 0 m/s to .999% of the speed of light. In an instant. Would that mean that the plank is accelerating faster than the pressure wave can travel through the material? What would happen, I mean, would the plank like warp in on itself or some crazy crap? This is driving me insane.
The pressure wave would still be traveling along the plank at the same speed relative to the rest of the plank as the whole thing was instantaneously accelerated. Nothing would change from the perspective of the plank accept the light coming toward or away from it would be warped severly. The plank would also shrink drastically along the direction of motion, but from the plank's perspective they wouldn't notice this. Also there would be some time dilation effects going on.

But none of that changes the fact that the pressure wave would still be traveling along the plank at the same speed it was relative to the rest of the plank as the whole thing is accelerating together.

They'd return to Earth.
If there where no more burns after the TLI the spacecraft would have reentered Earths atmosphere after going to round the moon and back to Earth. This was done so your scenario wouldn't happen if something went wrong on the way to the moon. Still they could've messed up their burn as long as the craft stays under 11km/s it'd return to Earth. What I dont know is how much error is allowed to still get a free return trajectory

Free Return Trajectory

They were already going faster than 11km/s a second...they had to break free of Earth's gravity well to get to the moon after all. What would have happened is that they would have slung out into space if they were burning uncontrollably in an accelerating manner as they rounded the moon. If they were decelerating uncontrollably as they rounded the moon, they would've either gone into an orbit, or if they burned way too long, they would've crashed.

They wouldn't have come back to the Earth unless they burned in exactly the right manner that would have allowed it, which is not what the question asked. The question asked what would've happened in an uncontrolled burn.
 
Assuming you can build something the full 1 light year length of the plank, and design the plank to respond to your force of choice and be durable enough, you can apply a very strong force to the full length of the plank simultaneously, from the point of view of the stationary plank. Now it's unlikely you'd be able to apply the force perfectly evenly and timely, so you could get all kinds of warping or even nuclear fusion from that, but ignoring that, the plank just accelerates to the designated speed. Then creates a nuclear explosion at the location of the button.

Reminds me of throwing a baseball at 90% of the speed of light.

My god, that was an amazing link. Freakin love that comic.

You didn't read the link I provided, did you?

Well, excuse me. It's wikipedia; of course I read it.

Also why would you spiral into the surface if you go below a certain altitude? There is nothing to decelerate you. As long as you aren't on a collision course with the surface to begin with you end up in space again after passing the moon.

I apologize. I was taking into account the moon's negligible atmosphere, which would really only have an effect if it was orbiting for quite some time (as in, millennia).

The pressure wave would still be traveling along the plank at the same speed relative to the rest of the plank as the whole thing was instantaneously accelerated. Nothing would change from the perspective of the plank accept the light coming toward or away from it would be warped severly. The plank would also shrink drastically along the direction of motion, but from the plank's perspective they wouldn't notice this. Also there would be some time dilation effects going on.

But none of that changes the fact that the pressure wave would still be traveling along the plank at the same speed it was relative to the rest of the plank as the whole thing is accelerating together.

Ah. I'm still a mite confused, but thanks for the explanation.
 
Any particular evolutionary reason opsin genes would be on the X chromosome? Or is it just one of those quirks of our genome?

I would have to speculate, as I'm familiar with this in reference to papers written about human / primate / mammal evolution and not a more broad understanding. So I'm not actually sure how reptiles manage tetrachromatic vision. But... I would speculate that the original evolution of tetrachromatic vision was rather like our more recent regaining of trichromatic vision, and that the fact the blue opsin gene got duplicated to the X chromosome allowed for more opportunities to gain further differentiated vision. In other words, because the blue opsin got duplicated to a sex chromosome, different alleles were able to come together in formerly dichromatic animals, creating new trichromatic individuals.

So it was a bit of a quirk, but the only type of quirk that could easily progress from dichromatic to more specialized vision. Had it happened differently, we would probably not be aware of the possibility that it ever could have happened. Like a lot of things in evolution, it's only a quirk in retrospect.
 
If a complex wavefunction can be written as Ψ = a + ib, why is (Ψ*)(Ψ) is always real?
The absolute value function on a complex number yields a real number (the imaginary recombines to real, when multiplied by itself).

http://www.regentsprep.org/Regents/math/algtrig/ATO6/absvlecomlesson.htm

If you're doing cross products (not sure what the asterix is supposed to mean in your post) it's still an absolute value since magnitudes are absolute values.
 
The asterisk is the complex conjugate, so turn i into -i. Then you're left with

(Y*)(Y) = (a + ib)(a - ib) = a^2 + b^2
 
Yep, I'll never get math.
 
A wavefunction f= A*exp(ikx) is multiplied with f* = A*exp(-ikx)
exponents of multiplied variables are summed, so we get
ff* = A^2*exp(ikx-ikx) = A^2
which is real
sqrt(ff*) = A
is the length of f

exp(ikx) = cos(kx) +i*sin(kx) = x+iy
as mentioned before
 
Is there any known relationship between t* and v (velocity)?

*If a human would live in a spaceship flying at almost the speed of light, then time would seem to pass normally for them, but to observers who have a normal velocity it'd look like they did everything in slow-motion, and they would (the astronaut) live on a lot longer than normal. Here t is the amount of time that seems to pass for a certain object divided to the amount of time that passes for an object with zero velocity in the same timespan.
 
Yup, that's it.
I dreamed that very formula (albeit under another form : v²/c² + t² = 1) last night (without ever having heard of it, of course - otherwise there'd not be much to say). I wondered whether I was just dreaming nonsense like usual or whether it was actually a real formula.
Now I just need to get a vision about something that has not been discovered yet ;)
Thanks for the answer.
 
Whoa, everyone out of the man's way, he dreamed of general relativity and time dilation.

Remember your friends here at CFC when you invent a teleporter.
 
Whoa, everyone out of the man's way, he dreamed of general relativity and time dilation.

Remember your friends here at CFC when you invent a teleporter.

Hello, this is the Strijder20 from the future. I have sent a time machine to you by mail which should arrive five minutes ago ;)

(It probably had to do with me reading a book about it right before going to sleep - not time dilation, but a related subject. Somewhere it said that for an object which travels at light speed the entire history of the universe passes in less than a second - or more accurately, no time, and if I remember correctly that's how I got to that formula :p)
 
It's entirely possible that you had simply seen the formula before, and you remembered it while dreaming. In a way, that's what dreams are for.

Definitely possible. I've read books which explain general relativity (but do not go into the details, and do not give many formulae) so I might have picked it up somewhere, I just can't remember ever having done so.
 
In high school a friend of my told he had a dream where the maths teacher asked how some set A is related to another set, b. In the dream he answered "A is greater than B", and the teacher called him stupid or something like that. At that time to call a set "greater" than another one sounded odd to me, unlike "bigger".

Later the teacher asked that kind of question, and the friend who sat at the front looked back at me and raised his hand to give the same answer as in the dream. The teacher didn't call him stupid though, but told that the answer was correct.

This friend had probably read Bell's "Men of mathematics" and didn't remember picking up the word from there. Although, if that's the case, he gave the answer just because he had seen it in his dream. :D
 
Can somebody give me a summary of the weighted determinants of metabolism.
 
Spoiler Gross question. Make sure you're not eating. :
How does constipation actually work? As in, what are all the biochemical mechanisms at play that cause it, and so forth?
 
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