/sci/ - Science & Math

Oh, a note:

While CAVE will only *install* on a Red Hat-based system, it appears that it will *run* on pretty much any Linux flavor, so long as it's still installed to /awips2/, without much fuss. So if you don't like RH, you can load a live CD and install it to disk that way.

Ok, with hurricane season getting underway, I thought it'd be nice to provoke some serious discussion about that universal idle topic of conversation. This general thread is experimental, so either it will catch on or it won't.

I'd love to hear from all storm chasers, professional meteorologists, weather station operators, atmospheric and hydrological researchers, pilots, mariners, and general weather buffs. Pretty much anything that's going on involving air and water on our little blue marble should be relevant, but PLEASE for the love of $DEITY avoid arguments about global warming/climate change, or /x/-tier tinfoil like HAARP and "chemtrails". Let's try to keep it concrete, practical, and empirical.

===Bookmarks===
Most of these are US-centric, but some are more generally applicable. As always, feel free to share your favorite weather sites.

World Meteorological Organization: http://www.wmo.int
US National Weather Service: http://www.weather.gov/
US Joint Typhoon Warning Center: https://metoc.ndbc.noaa.gov/JTWC/
ECMWF (Europe) Charts & Forecasts: http://www.ecmwf.int/en/forecasts
JMA (Japan) Typhoon Center: http://www.jma.go.jp/en/typh/
Weather prediction education: http://www.theweatherprediction.com/
Unisys Weather: http://weather.unisys.com/index.php
AWM Model Viewer: http://aweathermoment.com/model-viewer/
AWIPS II (software used by the NWS, free): http://www.unidata.ucar.edu/software/awips2/
NOAA Weather and Climate Toolkit: http://www.ncdc.noaa.gov/wct/
Twister

By the way, is there anyone here who's good with tensor calculus? I feel like I've been going in circles trying to understand the notation.

>>8095561
And the same can be said for Newtonian mechanics, and caloric theory, and classical electrodynamics. Yet we know all those theories break down under extremal conditions. Therefore, if causality is a correct description of the universe only in the limit of something, then it stands to reason that there are situations in which it no longer describes reality.

>>8094617
What the Alcubierrie metric allows you to do is get around the infinite energy requirement to accelerate an object past the the speed of light, and the effects of length contraction and time dilation on the travelling object. It does *not* remedy the possible violations of causality that can result from completing a round-trip through different inertial frames. If anything, it turns the causality violations from an unphysical hypothetical, into a potentially real hypothetical.

>>8094390
That's the thing: I've never heard of a rigorous explanation for why it should apply in all situations, and in all spacetime topologies.

I'm not the first to notice this. http://philsci-archive.pitt.edu/4690/1/CausalFundam.pdf
http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.129.191&rep=rep1&type=pdf
and
http://www.pitt.edu/~jdnorton/papers/003004.pdf
have all noticed this, but they've mostly come at it from a philosophical angle. I'm more interested in what the concrete implications are, assuming we define causality in a consistent way.

>>8094373
The speed of light is actually a semi-arbitrary scaling factor that connects our units for duration with our units for distance. In fact, right now it's not actually measured: it's *defined* by the SI, with the meter set from it by way of the caesium-transition second. Even though we percieve them as being different things, they're actually all just different components of spacetime.

>>8093651
I'm not sure I follow you. You can theoretically create a causal connection between events that would normally have a space-like separation using a Krasnikov tube to provide a timelike worldline between them. That doesn't itself break causality, at least not until you use a second one to make a return trip, but it does break the limitation on the speed of interactions from the perspective of a distant observer. So there has to be something more fundamental going on.

>>8093616
I'm talking about the effect a particular axiom has on the construction of physical laws. That's not philosophy, that's science.

>>8093624
Yeah, but if we drop our strict reliance on it as a fundamental postulate, then we open the possibility that certain extreme conditions can break it, even if those conditions are so extremely improbable in nature that they've never existed in the universe's history.

>>8093369
I didn't say acausality as such had been observed, certainly not at normal scales. My question is if it's possible that causality might a) be an emergent phenomenon of something which is acausal, and b) if that causality might itself break down under extreme conditions.

As for the "not all mathematical solutions are good physical solutions", well, then we still have to explain what those constraints are and why they exist. Physics tends to follow the math quite closely. No one had ever observed antimatter when Paul Dirac first wondered what would happen if he did't discard the negative solution to a particular quadratic term in the relativistic Schrödinger equation.

(cont'd)

While Newtonian gravity expressed the interaction of bodies in a basically acausal, yet simultaneous way, GR suggests that the bodies (represented by the stress-energy tensor) have an effect on the geometry of spacetime (the metric tensor), which then affects the bodies in turn (the geodetic equations). This might not be a problem, except for the fact that their exist valid solutions like the van Stocktum, Gödel, and Alcubierrie metrics allow you to create a circle of events which are still seperated by timelike intervals (closed timelike curves), which means you could have a seemingly paradoxical cyclic causality. To date, all responses to these metrics have been the suggestion of ad-hoc conjectures that invoke causality as some kind of universal force field, something which strikes me as desperate and unsound.

When one tries to natively combine the equations of relativity and QM, we get the timeless, acasual, and nonlocal Wheeler-DeWitt equation. This is presently interpreted as showing some essential incompatibility between GR and QM, but what if what that equation has been demonstrating, and we've been ignoring, is that this is precisely how the universe operates? That time, space, and therefore causality and locality, are merely emergent properties of laws which are have none of those things?

What would the implications be of ditching the reliance on causality? Is it even possible to make a coherent theory without it? Can we even prove that the universe is logically consistent in the first place?

I was mulling over some GR equations, when something hit me. We often say in physics that certain things can't be possible because they would violate causality, but just how well-founded is the invocation of causality to constrain a physical theory anyway?

Starting from classical physics, [math]F = ma[/math] really doesn't say anything, except to provide a meaning to the word "force", until we start attaching the implication that a force *causes* a mass to accelerate. Otherwise it, and everything else in Newtonian physics, is just a bunch of acausal couplings between expressions.

The problem gets hairier under relativity, because simultaneity now goes out the window. Two observers in different inertial frames cannot agree on the simultaneity of events, yet it is asserted that they can still agree on a partial ordering of some events, so long as a lightlike or timelike interval seperates them.

(cont.)

>>8079286
Did you try replacing the breadboard?

>>8077498
It would help if you could summarize your calculations for us. Hard to know what the mistake is otherwise.

>>8068395
Yet the principle holds. The simplest, if perhaps least elegant way of going about it, is to take a universal constructor (a machine which can build anything given the right instructions and raw materials), and slap a Turing machine (universal computer) onto it. The latter already exists. The problem is that the only such universal constuctors we know of, are the machinery of cellular reproduction.

>>7968768
Nah, depends on which orbit it was in and how many pieces you break it into. Plus there are methods to deorbit space junk. They're just not used right now because there's no big need for them.

>>7968746
As long as you can get into an orbit that's sufficiently higher that gravity can do most of the work for you. Remember that there's still 90% of surface gravity in orbit.
>>7968749
The concept of "rods from God" has already been floated around for a long time. The idea is they would make great bunker-busters.

>>7968732
No, they don't, because that's actually a great way to break something that's in a lower orbit than you, or possibly injure someone on earth. Tiny objects like that don't ablate very much, so you could probably puncture someone's skull with that dead AA battery you thought would be fun to eject.

>>7968709
You could not humanly provide enough [math]\Delta v[/math] to successfully deorbit.

>>7968681
Might depend on the starting orbit. What you're basically doing there is performing an orbital transfer.

>>7968665
It has nothing to do with that. Once you're in orbit, it actually takes force to leave. A small amount of atmospheric drag might provide that, but the rate of orbital decay on an object with such a small cross section would be so minuscule you'd probably freeze to death first.

>>7967886
Oh, you mean like global warming denialism?

UPDATE:
http://www.spc.noaa.gov/products/md/md0283.html

That scaly thing running up from Texas to Kansas is a dry line. With the cold front following behind it, that's basically perfect tornado weather.

I would advise all anons in that vicinity to be alert for all weather advisories over the next few days.