## Search found 1911 matches

Wed May 09, 2012 4:17 am UTC
Forum: Science
Topic: Big big planet
Replies: 48
Views: 6853

### Re: Big big planet

That's correct. And made me come up with an interesting problem. Imagine a spherical shell of point masses, that do not interact with each other. Such a configuration is stable, since there's no forces anywhere. No place a large mass M inside the shell, but off-centre. The attraction from the mass ...
Mon May 07, 2012 5:26 am UTC
Forum: Science
Topic: Big big planet
Replies: 48
Views: 6853

### Re: Big big planet

So each hemisphere has mass 2*pi*r 2 *thickness * density, and a center of mass at 3/8*r. So the gravitational force between them is G*256/9*pi 2 *r 2 *thickness 2 *density 2 . You cannot contract the half-spheres to their center of mass like this is possible with spheres. You have to integrate the...
Sat May 05, 2012 7:54 am UTC
Forum: Science
Topic: Big big planet
Replies: 48
Views: 6853

### Re: Big big planet

This is confusing. Both my calculation and Charlie!'s are correct, near as I can tell. Yet they give contradicting answers. The trick is that it's not the mass that goes into the calculation, but the product of the masses of the two things attracting each other, so there's a factor of m^2, or r^4. ...
Sat May 05, 2012 12:38 am UTC
Forum: Science
Topic: Big big planet
Replies: 48
Views: 6853

### Re: Big big planet

Hm, interesting. So each hemisphere has mass 2*pi*r 2 *thickness * density, and a center of mass at 3/8*r. So the gravitational force between them is G*256/9*pi 2 *r 2 *thickness 2 *density 2 . What determines the (highest possible) breakdown size is when the compressive strength of your object (in ...
Fri Apr 27, 2012 6:49 am UTC
Forum: Fictional Science
Topic: Things a Perfect logician would Discover
Replies: 40
Views: 14152

### Re: Things a Perfect logician would Discover

Facts. They would discover facts. It might also be helpful to think of the things they would not discover, which would fall under the category not facts.
Fri Apr 27, 2012 6:40 am UTC
Forum: Science
Topic: A potentially super-offensive question about Hawking.
Replies: 16
Views: 4192

### Re: A potentially super-offensive question about Hawking.

EdgarJPublius wrote:It is a fundamental misconception that just because physics pioneered fifty years ago
I don't want to make you feel old, but... Hawking's most famous paper was published almost 40 years ago
Sun Apr 22, 2012 5:31 pm UTC
Forum: Science
Topic: Taking the 'mind' from the brain and putting elsewhere
Replies: 6
Views: 3457

### Re: Taking the 'mind' from the brain and putting elsewhere

Nit-picking time! :) As the (be it human or non-human) brain is, by our own criteria, one of the best and most readily available kinds of intelligence. For me, it is only natural to start with the science that attempts to understand the brain, Psychology. The first sentence here just ends suddenly -...
Tue Apr 17, 2012 12:56 pm UTC
Forum: Science
Topic: What is Many Worlds? What isn't Many Worlds?
Replies: 125
Views: 14649

### Re: What is Many Worlds? What isn't Many Worlds?

doogly wrote:I was expressing my deep elation at dismissing MW. It is awful stuff.

Aw, cmon It's really useful for picturing entanglement. You don't have to have any changes propagating faster than light, because the measurement is a change to the measuring apparatus, not to the particles.
Sat Apr 14, 2012 4:40 am UTC
Forum: Science
Topic: What is Many Worlds? What isn't Many Worlds?
Replies: 125
Views: 14649

### Re: What is Many Worlds? What isn't Many Worlds?

So for different sequences of 0s and 1s, we can grant for the sake of your argument that a bunch of other atoms that we don't care about get affected (though we could regenerate the same problem if we started caring about those atoms) and so the different 0 and 1 states become more different. But w...
Sat Apr 14, 2012 1:03 am UTC
Forum: Science
Topic: What is Many Worlds? What isn't Many Worlds?
Replies: 125
Views: 14649

### Re: What is Many Worlds? What isn't Many Worlds?

In your harddrive example, even if your harddrive starts in an indeterminate state it will quickly decohere into a set of classical states of some 0s and 1s, and the probabilities will become classical Okay. So for different sequences of 0s and 1s, we can grant for the sake of your argument that a ...
Fri Apr 13, 2012 5:24 pm UTC
Forum: Science
Topic: What is Many Worlds? What isn't Many Worlds?
Replies: 125
Views: 14649

### Re: What is Many Worlds? What isn't Many Worlds?

After one measurement, your wavefunction contains 10 observers, unambiguously. Well, the problematic thing about assigning probabilities that way is that the wavefunction can contain those same observers before , too. For example, if we have a computer hard drive with a bunch of possible 0s and 1s,...
Mon Apr 02, 2012 3:54 am UTC
Forum: Science
Topic: [Homework Help] Quantum Physics I
Replies: 14
Views: 3590

### Re: [Homework Help] Quantum Physics I

Graham-schmidt is a good place to go when you don't know what else to do, but it requires starting material. I suppose you could start with the identity matrix, then find the equation for an arbitrary matrix orthogonal to the identity matrix. Then choose an arbitrary (or not arbitrary) matrix that s...
Sat Mar 31, 2012 9:39 pm UTC
Forum: Science
Topic: Exponential of Operators
Replies: 4
Views: 6404

### Re: Exponential of Operators

If A and B could commute, sum of (A+B)^n / n! would look exactly like eA eB. If A and B can't commute, where do the commutators come in? Can you turn that into the exponential?
Wed Mar 28, 2012 7:10 am UTC
Forum: Science
Topic: What is Many Worlds? What isn't Many Worlds?
Replies: 125
Views: 14649

### Re: What is Many Worlds? What isn't Many Worlds?

Consider the amount of probability within some distance 'a' of the middle. First you take the limit as the number of trials -> infinity (always 1). Then you take the limit a-> 0. Seems like my calculus 2 section on delta-epsilon limits all over again :P However, if you reverse the order of these sim...
Mon Mar 26, 2012 4:19 am UTC
Forum: Science
Topic: What is Many Worlds? What isn't Many Worlds?
Replies: 125
Views: 14649

### Re: What is Many Worlds? What isn't Many Worlds?

The author, however, might not know the origin of a probability if it came up and bit him in the face. For example section A. When agents in a classical multiverse flip a bunch of coins and follow some probability-updating procedure, the author faults the ones who flipped all heads for coming to th...
Mon Mar 26, 2012 1:43 am UTC
Forum: Science
Topic: Worst thing you've seen in a lab
Replies: 256
Views: 230644

### Re: Worst thing you've seen in a lab

I had an incident in my 9'th grade 'geo-science' class where the teacher was showing us how sodium burned in water. She had a huge 2lb block of it and would shave off a little bit to drop it in a big clear pot. She got called outside by campus security, and some dumb student desided to go up and dr...
Mon Mar 26, 2012 1:34 am UTC
Forum: Science
Topic: What is Many Worlds? What isn't Many Worlds?
Replies: 125
Views: 14649

### Re: What is Many Worlds? What isn't Many Worlds?

Is there a variant of MWI that says that the branches of the multiverse where the Born Rule fails simply don't "materialize", or is that just a bit too ad hoc? The Born rule failing is not an inherent property of a state - even if you flip a coin 100 times and they're all heads, it could ...
Sun Mar 25, 2012 6:53 am UTC
Forum: Science
Topic: What is Many Worlds? What isn't Many Worlds?
Replies: 125
Views: 14649

### Re: What is Many Worlds? What isn't Many Worlds?

Actually, I just finished reading Everett's paper you linked and his argument for the Born probabilities seems more general than he lets it be. He defines probability only as the limit of a large number of trials, which is not all that it is (see: Bayesian probability). Please continue reading the ...
Sat Mar 24, 2012 9:28 am UTC
Forum: Science
Topic: What is Many Worlds? What isn't Many Worlds?
Replies: 125
Views: 14649

### Re: What is Many Worlds? What isn't Many Worlds?

The no-collapse theories are in theory experimentally different from the collapse-interpretations. Deutsch wrote an interesting article in the book Quantum Concepts of Space and Time outlining some possible tests you could do (with magical technology that doesn't yet exist). The key point is that c...
Fri Mar 23, 2012 10:46 am UTC
Forum: Science
Topic: What is Many Worlds? What isn't Many Worlds?
Replies: 125
Views: 14649

### Re: What is Many Worlds? What isn't Many Worlds?

I'm certainly no expert on the matter, but, whilst MWI certainly doesn't immediately work as an attempt to derive the Born rule, if such a rule is inserted manually it's still no worse off than the various other interpretations. So, why isn't more common to take as axiomatic that, at any point wher...
Sun Mar 11, 2012 9:59 pm UTC
Forum: Science
Topic: Would a tiger make a good pet for Paul Bunyan?
Replies: 10
Views: 6543

### Re: Would a tiger make a good pet for Paul Bunyan?

And I guess that follows, since they're more social than really any other species of feline. Also, holycrapthatwasadorable. Edit: Also, this comedy swear check thing is baffling and actually a little annoying. Hulk likes centipede, etc. Yeah, it goes in cycles. The philosophy is that we pay the rno...
Sun Mar 11, 2012 6:08 am UTC
Forum: Science
Topic: [SOLVED] Refraction of light
Replies: 14
Views: 4723

### Re: Refraction of light

The individual photons are still waves. Quantum mechanics, eh? So if you understand why waves will change direction, you realio trulio understand why the photons change direction.
Sun Mar 11, 2012 6:02 am UTC
Forum: Science
Topic: Would a tiger make a good pet for Paul Bunyan?
Replies: 10
Views: 6543

### Re: Would a tiger make a good pet for Paul Bunyan?

Sat Mar 10, 2012 1:44 am UTC
Forum: Science
Topic: Space elevators and angular momentum
Replies: 7
Views: 2370

### Re: Space elevators and angular momentum

Yeah, it seems reasonable. Basically the angular momentum is going to need to come from the torque by the cable, which will then pull on both the satellite and the earth. But if the satellite is above geostationary orbit there will be this tension keeping it up, so everything will be fine.
Fri Mar 02, 2012 3:53 pm UTC
Forum: Science
Topic: Nitrogen Dioxide as a Second Messenger signal?
Replies: 5
Views: 2952

### Re: Nitrogen Dioxide as a Second Messenger signal?

Whoa. Biology is complicated.
Wed Feb 29, 2012 4:31 am UTC
Forum: Science
Topic: Angular Momentum
Replies: 13
Views: 3793

### Re: Angular Momentum

I'm pretty sure photons always have angular momentum of +hbar or -hbar and can't have an angular momentum of 0. In the direction of movement, or in other directions? ;) Space is 3-dimensional (well, 4 with time), so the system is a bit more complicated. Hmm, interesting puzzle. The photon must alwa...
Wed Feb 29, 2012 1:57 am UTC
Topic: What's Best for the World
Replies: 51
Views: 9652

### Re: What's Best for the World

http://www.youtube.com/watch?v=6PQ6335puOc Assuming you don't want to go the Full Conan... If the goal is to feel like you're making a difference, maybe become a doctor or civil engineer or something and then volunteer with a Without Borders charity. If you want to save lives, making a lot of money ...
Fri Feb 24, 2012 9:16 pm UTC
Forum: Science
Topic: Poke Holes In My Idea!
Replies: 27
Views: 5022

### Re: Poke Holes In My Idea!

The main trouble I see with this is that it simply doesn't make sense given how we know electrons scatter photons - they don't act like solid spheres. Also, similar to the kinetic theory of gravity mentioned earlier, this predicts odd things for moving particles (on the other hand, there's a small c...
Tue Feb 21, 2012 1:17 pm UTC
Forum: Fictional Science
Topic: Space Combat
Replies: 30
Views: 8408

### Re: Space Combat

If you have a laser aperture with a diameter of 5 meter then with a wavelength of 500nm you can focus it down to 5cm for a factor 10 4 increase in intensity at a distance on the order of 500km. At earthly missile speeds that would give minutes to destroy it. Although a railgun in space could get go...
Sat Feb 18, 2012 10:50 am UTC
Forum: Fictional Science
Topic: If you could change the laws of physics...
Replies: 50
Views: 28656

### Re: If you could change the laws of physics...

I suppose I'd make it more life-friendly. Maybe a quasi-steady-state universe, with no accelerating expansion? Maybe the scale of the universe could oscillate, but not dramatically enough to kill off prepared civilizations. Allowing for spontaneous entropy decrease would be good if we wanted our lon...
Thu Feb 16, 2012 6:44 pm UTC
Forum: Science
Topic: Dark Matter
Replies: 21
Views: 2787

### Re: Dark Matter

How would you make something if you can't interact with it non-gravitationally? As far as I know, making something and detecting something can only use the same set of interactions. Maybe produce it near black holes?
Sun Feb 12, 2012 10:26 am UTC
Forum: Fictional Science
Topic: Reactionless Drives
Replies: 3
Views: 3802

### Re: Reactionless Drives

You can't directly get out energy from changing velocity, you'd need contact with some outside object to be able to run your generator. "Some outside object" could still be inside the ship, though, as long as the motor has to exert a force to get this object to move.
Sat Feb 11, 2012 9:43 pm UTC
Forum: Science
Topic: Would chocolate kill velociraptors?
Replies: 36
Views: 7698

### Re: Would chocolate kill velociraptors?

chiisanatantei wrote:Chocolate is poison to many animals, including birds, so would it also kill velociraptors?

Worth a shot
Sat Feb 11, 2012 7:32 pm UTC
Forum: Science
Topic: Some quantum queries
Replies: 5
Views: 1512

### Re: Some quantum queries

Third one: I measure, say, the momentum in the x-direction of some particle causing its momentum wavefunction to collapse. Then the momentum wavefuntion p x is given by a dirac delta function and the Heisenberg uncertainty principle seems to suggest that the uncertainty in the particle's x-position...
Thu Feb 09, 2012 3:17 am UTC
Forum: Fictional Science
Topic: Artificial Gas Giant Surface
Replies: 22
Views: 7654

### Re: Artificial Gas Giant Surface

Turtlewing wrote:It might matter when in the human's life-span you started the acclimation. I'd expect children by virtue of being smaller, and still developing physically could adapt more reddily than an adult.

Or it could interfere with their development.
Wed Feb 08, 2012 2:26 am UTC
Forum: Science
Topic: Building an MDP Thruster. Need help with ignition circuit.
Replies: 4
Views: 1524

### Re: Building an MDP Thruster. Need help with ignition circui

Ionizing radiation, either from a UV source or radioactivity, if you're fine with it being sloooooowwwwwwwwwwwwwwwwwww.
Sat Feb 04, 2012 4:20 am UTC
Forum: Science
Topic: Common Misconceptions within Physics and Astronomy
Replies: 98
Views: 17801

### Re: Common Misconceptions within Physics and Astronomy

I think that before we venture into the unknown territory of discussing Quantum Mechanics, how about we actually, actively eliminate misconceptions? http://www.amazon.com/Modern-Quantum-Mechanics-2nd-Sakurai/dp/0805382917 :lol: Or, on the other hand, we could always listen to the guy with the red te...
Wed Feb 01, 2012 5:58 am UTC
Forum: Science
Topic: Anti-matter = repulsive gravity?
Replies: 49
Views: 11789

### Re: Anti-matter = repulsive gravity?

The biggest conflict with what I know of is with the mass-energy equivalence in general relativity. Energy curves space just like mass does. And we know that antimatter has positive energy because if you collide an electron and a positron, you get two 511 keV photons.
Tue Jan 31, 2012 5:10 am UTC
Forum: Science
Topic: Black light from Camera Flash
Replies: 10
Views: 6353

### Re: Black light from Camera Flash

Yes, if you could coat it with the stuff they coat black lights with (though it would be pretty dim, unless it had a really high color temperature). But a little searching makes it feel unlikely that you'd be able to actually coat a flash tube with the right stuff. You could either stick a professio...
Mon Jan 30, 2012 4:00 am UTC
Forum: Science
Topic: Science needs a symbol
Replies: 83
Views: 12669

### Re: Science needs a symbol

Here's an image of the candle in the dark suggestion made by idobox, which was my initial thought as well. candle.jpg Of course, a more stylized version might be preferable. Put the candle inside of a Delta, showing the change in understanding as the scientific community adds to and revises what we...