Want to read Slashdot from your mobile device? Point it at m.slashdot.org and keep reading!

 



Forgot your password?
typodupeerror

Comment: Re:more simplifications and fewer cats, please (Score 1) 172

by Khashishi (#48637775) Attached to: Quantum Physics Just Got Less Complicated

I think people are moving away from the Copenhagen interpretation to other interpretations such as consistent histories, decoherence, and many worlds. Bohmian interpretation is another option, but I find it inelegant and it doesn't hold too much sway.

Personally, I feel that consistent histories* is the best. In this interpretation, the cat is simply dead or alive. We don't know which until we check, but the cat's state didn't change when we opened the box. Note that whatever is enforcing consistency does not obey causality---the laws of quantum mechanics are essentially symmetric in time (more accurately CPT). In some sense, the future is "prewritten" though we have no way to measure it, and the current state of the universe is required to be consistent with the future state. So if the cat is dead in the future where the box is opened, it's already dead with the box closed.

I prefer the "block universe" depiction of the universe as a stationary 4D object, since it seems to be easiest to reconcile with relativity. Relativity of simultaneity makes no sense if the future isn't already written. We call this 4D universe object a history, and all the events in the history have to be consistent with laws of physics. It makes no difference if you think of the past causing the future or the future causing the past: they are just there and neither is created from the other. In the many worlds interpretation, every possible (e.g. consistent) history exists, but I think one is sufficient.

*I might be mistaken on what consistent histories is. My description is my personal interpretation, which might coincide with the definition of consistent histories.

Comment: Re:von Neumann probes (Score 1) 321

Travel time. The galaxy is some 100000 light years across. Using available fuels, what fraction of light speed can a probe hope to achieve? Let's suppose they run on DD fusion energy. The reaction gives off about 0.4% of the rest energy of the fuel, so a reasonable estimate of potentially attainable specific impulse is 0.004*c, assuming the probe is mostly fuel. Using Tsiolkovsky rocket equation, how fast can a probe reasonable reach? This depends on how much fuel the probe eats up at each stop. Assuming a probe mass of 100g, lets suppose the probe eats up a mass of Jupiter to create fuel at 10% efficiency at each stop. Well, that gives a delta v of ~.25*c. (Since there is a logarithm, the result doesn't change that much if we eat a sun or a saturn.) Useful cruise speed is half of that. Ok, that is still enough speed to conquer the galaxy in a few million years.

Multiplication factor: how many probes need to be sent out after each stop such that there is enough to spread over the galaxy in a reasonable time (there are ~10^11 stars). This is increased by the fact that many probes will fail to reach the destination for various reasons, so some redundancy is needed. We want to choose a multiplication factor such that the probes will cover the galaxy in approximately the same time as it takes for one probe to travel across the galaxy. Assume probes travel at 0.1*c, and it takes 10^6 years to traverse the galaxy. Let's assume a distance of 20 light years, or 200 travel years between stops. So we have 5000 stops in 10^6 years, so we need a multiplication factor of
f = 1.005 * redundancyFactor.
Ok, that's small enough to not make much difference in the resource needs.

Hmm, I intended to show that it was unfeasible, but it still looks like it might be physically possible, given extremely powerful probe technology.

Comment: Re:This might alienate anti-ISI* Muslims. (Score 1) 225

by Khashishi (#48568849) Attached to: US Navy Authorizes Use of Laser In Combat

Silly rabbit, laws of war don't apply to dealing with unlawful combatants.

Also, lasers are fairly well collimated, so you'd have to aim directly at the person to blind them, and then I think they would have more problems than just blinding. You can also blind someone by shooting them in the eye with a gun, but for some reason it's ok as long as they have a good chance of dying outright.

Comment: women are objects in India (Score 0) 180

by Khashishi (#48549445) Attached to: Uber Banned In Delhi After Taxi Driver Accused of Rape

I have a friend who got back from a trip to India. She was traveling in a group with some other women and one man. The taxi drivers would grab the women by the arms and force them in the car like luggage, and then talk with the man about where he would like to go (with his women). My friend had bruises on her arms from repeated grabs.

Comment: Re:Matters of Scale (Score 1) 213

by Khashishi (#48509193) Attached to: Game Theory Analysis Shows How Evolution Favors Cooperation's Collapse

Capitalism is about owning and trading things, not about making things. Certainly making things is a big part of owning them, and is a big drive of the capitalist model, but it is not a defining feature, as all societies make things. A defining feature is owning and trading things that are not (human) made, such as land, water rights, and the electromagnetic spectrum.

Man will never fly. Space travel is merely a dream. All aspirin is alike.

Working...