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Comment: Re:Statistical proof for turtles all the way down (Score 1) 231

by As_I_Please (#48881737) Attached to: The Paradoxes That Threaten To Tear Modern Cosmology Apart

This depends on the possible quality and size of a universe simulation. Is it possible to simulate the entirety of a universe using only a finite subset of that universe?

If yes, then there are (at maximum) an infinite number of simulated universes and and infinite number of recursively simulated universes. Thus the probability of us being the root/real universe is zero ("of measure zero" if you ask a mathematician). Perhaps the holographic principle comes into play to allow the entire universe to be simulated without using the resources of the entire universe.

If no, then there can be only a finite number of simulations in the observable universe. Also, each of the simulated universes is a smaller and/or less-precise version of the simulating universe. In this case, there are (at maximum) a finite number of simulated universes and a finite number of recursively simulated universes capable of hosting intelligent life (a cellular automata with only one cell could hardly be called intelligent). In this scenario, there is a non-zero probability that we live in the root/real universe.

I lean towards no, but I don't have any evidence, just a bias for thinking myself real.

Comment: Re:Energy is not conserved in General Relativity (Score 1) 231

by As_I_Please (#48881629) Attached to: The Paradoxes That Threaten To Tear Modern Cosmology Apart

True, in a contracting universe, photons gain energy. Noether's theorem says that energy conservation is a consequence of time translation symmetry (t -> t + constant), not reversal symmetry (t -> -t), so conservation of energy isn't required. The "energy imbued by the creation of the universe" seems ill-defined. If you believe Hawking and Krauss, this energy is zero.

Comment: Re:Energy is not conserved in General Relativity (Score 1) 231

by As_I_Please (#48881261) Attached to: The Paradoxes That Threaten To Tear Modern Cosmology Apart

Read the blog post I linked to above. There's no way to consistently assign an energy density to spacetime curvature. Quoting Prof. Carroll:

[U]nlike with ordinary matter fields, there is no such thing as the density of gravitational energy. The thing you would like to define as the energy associated with the curvature of spacetime is not uniquely defined at every point in space. So the best you can rigorously do is define the energy of the whole universe all at once, rather than talking about the energy of each separate piece. (You can sometimes talk approximately about the energy of different pieces, by imagining that they are isolated from the rest of the universe.) Even if you can define such a quantity, it’s much less useful than the notion of energy we have for matter fields.

Comment: Re:Energy is not conserved in General Relativity (Score 1) 231

by As_I_Please (#48881237) Attached to: The Paradoxes That Threaten To Tear Modern Cosmology Apart

Consider the region of space that contains the photon. If each dimension of the universe double in size, then the photon loses half its energy. But, the vacuum energy increases by a factor of 8 (volume increases by 8 since space is 3 dimensional). This process can't keep energy constant.

You can also reason that different photons will lose different amounts of energy depending on the energy they started with. There's nothing to keep these changing energies balanced with the vacuum energy in expanding or contracting space.

Comment: Energy is not conserved in General Relativity (Score 5, Interesting) 231

by As_I_Please (#48871403) Attached to: The Paradoxes That Threaten To Tear Modern Cosmology Apart

It has been known for quite some time that energy is difficult to define rigorously in General Relativity. A good explanation can be found in this post by CalTech physicist Sean Carroll. Key point:

The point is pretty simple: back when you thought energy was conserved, there was a reason why you thought that, namely time-translation invariance. A fancy way of saying “the background on which particles and forces evolve, as well as the dynamical rules governing their motions, are fixed, not changing with time.” But in general relativity that’s simply no longer true. Einstein tells us that space and time are dynamical, and in particular that they can evolve with time. When the space through which particles move is changing, the total energy of those particles is not conserved.

As a simple example, imagine a photon traveling through an expanding universe in a region with no other matter or energy (dark or otherwise). The expansion of space stretches the wavelength of the photon (cosmological redshift, which is distinct from Doppler redshift), causing it to lose energy. The photon loses energy with nothing around it gaining. Energy is lost because spacetime itself is changing, so Noether's theorem doesn't apply.

Comment: Re: might not be as good as you think (Score 1) 173

by As_I_Please (#48606429) Attached to: The GPLv2 Goes To Court

How do you let people know what the compiler does? Unless there's a human-readable spec, people can't plan for future code/contracts. Writing random code/contracts and seeing if it "compiles" is not a great way to program/negotiate.

Doing the same thing every time is only a prerequisite for being correct. What if most people don't like what the current compiler does? After editing, how do you let people know what changed? How do you even know the compiler is correct without a human-verifiable document of expected behavior?

If a new version of the compiler comes out, does that mean that all previous versions were interpreting code incorrectly? Is there any existing compiler that behaves correctly?

When will the questions stop?

Comment: Re:kphotoalbum is the best in my opinion (Score 1) 259

by As_I_Please (#48599583) Attached to: Ask Slashdot: Best Software For Image Organization?

I second this. KPhotoAlbum was specifically made for fast tagging. Tagging 1,000 images with places, people, interesting things, etc., in half an hour is pretty normal for a session. As for lock-in, your image tags are kept in an all-text XML file. I run it off of Gnome and XFCE and don't notice any problems.

Comment: Re:Got you, Mrs. Sampson (Score 1) 80

No exception. Rule #1 is broken by reviving old forms and rules, usually with a Neo- prefix. First examle that comes to mind is Stravinsky's Neoclassical period. Compare The Rite of Spring (which gave birth to the Modern period of classical music) to his Italian Suite, which was the first of his Neoclassical pieces, written seven years later.

Comment: Re:Which side is upwards? (Score 1) 120

Rotating the nut clockwise always moves it away from you; rotating it counter-clockwise always moves the nut towards you. You're flipping your position axes (looking from the top/bottom) but keeping your velocity axes the same (moving in the same direction), hence the direction of rotation flips.

+ - Teacher Goes Back To Classroom After Being Removed For Science Fair Project

Submitted by As_I_Please
As_I_Please (471684) writes "In a followup to a previous story, Greg Schiller, a high school biology and psychology teacher in the Los Angeles Unified School District, returned to his classroom this past Monday after two months of suspension. The suspension came after complaints that two of his students built allegedly dangerous science fair projects: a pneumatic marshmallow launcher and a coil gun capable of launching a metal projectile several feet.

In addition to students being deprived of a qualified teacher for two months with just a week before AP exams, the school's fencing team was without a coach and could not compete in competitions, and the teacher's union was without their representative during contract negotiations.

The school district has not announced whether it will pursue any other disciplinary action."

Byte your tongue.

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