Annoying Questions I'd Like Answered...

Koumei · Post by **Koumei** » Mon Jul 23, 2012 9:47 am

Well, it's busy around the house in the evening/at night. You know, when no cafes are open in South Ausfailia (everything closes at 5PM), and when it's too dark to walk the dog. I'm not really that comfortable going out alone at night anyway.

And they very specifically don't have a wireless router here so they can monitor my 10yo sister's Internet access and make sure she's not on inappropriate sites (they're not worried about porn, they're worried about her joining a social media thing and then getting targeted by a kodiak bear pretending to be one of her friends).

But I might look into the cost of getting one of those dongle things that gives just your computer wireless Internet, and then pretty much live out of my room like before. And at least my stepsister has moved back in with her boyfriend and taken her kid with her.

hyzmarca · Post by **hyzmarca** » Mon Jul 23, 2012 6:56 pm

If a wireless router isn't appropriate, there's always the next best (and in some ways better) solution of a drill, and a spool of cat5e cable, some duct tape, and a couple of jacks.

sabs · Post by **sabs** » Mon Jul 23, 2012 6:59 pm

You can also have a wireless router that only allows specific mac addresses, and blocks everyone else completely.

Prak · Post by **Prak** » Mon Jul 23, 2012 8:17 pm

Hell, put a password on the signal.

Hicks · Post by **Hicks** » Tue Jul 24, 2012 6:38 pm

Several times in times past, I have read that faster than light travel violates causality, yet I have not figured out why this said. Would someone please break it down, barny style, to help me understand?

virgil · Post by **virgil** » Tue Jul 24, 2012 7:13 pm

The following is known as the Tachyon pistol duel thought experiment. It demonstrates why FTL travel results in time paradoxes. For simplicity of calculation's sake, FTL is considered to have infinite speed, striking its target instantly. The same effects apply with limited FTL velocities, but they are a bitch to do the number crunching with.

Man A and Man B meet at a point in space, and agree to turn around, move away from each other, count down 8 seconds, then turn and fire their weapons at each other. We will follow from man A's perspective.

Both parties exit and travel away from each other at 0.866 C. Man A counts down to 0, turns and then fires. Due to time dilation, when Man A counts to zero, Man B has only counted down to 4, thus his shot flies past Man B at 4 seconds.

Enraged that Man A has fired before he has hit 0, he fires at 4 seconds, and due to time dilation, man A has only counted down to 6! It strikes man A and kills him dead after he has counted down only 2 seconds, a full 6 seconds before he fired his initial shot. A classic grandfather paradox. It gets made worse by the fact that if you started from man B's perspective instead of man A, the exact inverse happens, with man B dead 6 seconds before he fires his shot instead.

So we're not only left with a grandfather paradox, but 2 events that both should have happened, but are mutually exclusive.

Please note that the time dilation is a proven phenomenon, and actually needs to be factored in for our GPS satellites to function.

fectin · Post by **fectin** » Wed Jul 25, 2012 1:11 pm

Because "faster than light" is meaningless. It's all relative to something.

virgil · Post by **virgil** » Wed Jul 25, 2012 1:17 pm

fectin wrote:Because "faster than light" is meaningless. It's all relative to something.

Light itself isn't relative, which is one of the core precepts of relativity. From every frame of reference, light goes at c in a vacuum. It's an effect of time dilation, making c remain the same from another PoV. Therefore, going faster than light actually means something.

tussock · Post by **tussock** » Thu Jul 26, 2012 3:04 pm

299,792,458 meters is physically one second away, because it just is. When you move at infinite speed it still takes a second to get there, because it just does. Relativity has predicted endless amounts of crazy horse shit that all turned out to be perfectly true. You can't go faster than light speed because light speed really is infinitely fast in a very real physical and mathematically true sense. Distance and time are sort of the same thing under the hood.

Which was all shown by Maxwell in the 19th century by investigating electric and magnetic fields, but no one understood what it meant at the time because obviously space and time aren't the same damn thing, only what is "obvious" about reality isn't real.

Solid things are 99.99% nothing. Void. Really. Infinite speed is also the speed of light, which everyone measures as the same finite ratio of meters to seconds, because that number describes the structure of reality in a very fundamental way.

CatharzGodfoot · Post by **CatharzGodfoot** » Sat Jul 28, 2012 2:50 am

tussock wrote:You can't go faster than light speed because light speed really is infinitely fast in a very real physical and mathematically true sense. Distance and time are sort of the same thing under the hood.

Which was all shown by Maxwell in the 19th century by investigating electric and magnetic fields, but no one understood what it meant at the time because obviously space and time aren't the same damn thing, only what is "obvious" about reality isn't real.

Solid things are 99.99% nothing. Void. Really. Infinite speed is also the speed of light, which everyone measures as the same finite ratio of meters to seconds, because that number describes the structure of reality in a very fundamental way.

Surprise! You don't know what "infinite" means.

Quantumboost · Post by **Quantumboost** » Sat Jul 28, 2012 5:03 am

The speed of light isn't infinite, it's just the tangent of the angle of your Past and Future causality cones relative to a reference frame's Time axis. It takes infinite *Energy* to get non-zero-mass causal particles to that speed relative to your reference frame, but that's just shorthand for "you can't do that".

Hicks wrote:Would someone please break it down, barny style, to help me understand?

I'll give it a shot.

Now, at every point in Spacetime is an Event. That Event either has a thing there or doesn't have anything there, but it is an Event none the less. These events can be represented like this:

Everything that is in the Past Light Cone of an Event is its Past, which affects it; everything that's in its Future Light Cone together makes up its Future, which it affects. Whatever it isn't affected by and doesn't affect is its Present.

How things are shaped within the Past, within the Future, or within the Present depends on your Reference Frame - and that is different if you're moving at a different speed, or in a different direction.

Now, let's call your present location A, and suppose you have a FTL communicator that lets you send a message to someone at the "same time", which means along a line in the Present that depends on how fast you're going in which direction.

Let's say you're throwing a party at your place, and your best friend is on his way. You use your Comm to send a message to him, because he was hanging out a couple stars away and you want to know where he is NOW. The message gets to him at point B, along your "same time line":

Now, B *also* has a handy FTL communicator, and he realizes that you're really nervous and sends off a reply right away. He's moving as fast as he can toward you in his spaceship, though, so while his "same time line" IS in his Present, it isn't the same as yours:

So his message travels along that "same time line" right to you. But "when" it gets there, you're at Event C:

which is in your Past, but his Present.

Doing this with comms that send it along a pseudo-future (i.e., not at the "same time" but still within the Present) is a bit more difficult, because you have to use either further distances or faster speeds - but it's basically the same idea.

tussock · Post by **tussock** » Sat Jul 28, 2012 9:52 am

@Catharz, very funny. And yes, light speed is infinitely quick. Guess how long it takes mass to travel billions of light years travelling at (all but) light speed?

No time at all! Funny that. Billions of years still pass in the static universe, but light speed travel really is infinitely fast for those doing it.

Juton · Post by **Juton** » Sat Jul 28, 2012 11:27 am

tussock wrote:@Catharz, very funny. And yes, light speed is infinitely quick. Guess how long it takes mass to travel billions of light years travelling at (all but) light speed?

No time at all! Funny that. Billions of years still pass in the static universe, but light speed travel really is infinitely fast for those doing it.

Are you retarded or just a troll? I think you are trying to say that if you are traveling at light speed then travel seems instantaneous from your point of reference. But it takes one year to travel a light year going the speed of light, that's why it's called a 'light year'. Instantaneous is not the same thing as infinite.

...You Lost Me · Post by **...You Lost Me** » Sat Jul 28, 2012 12:49 pm

tussock wrote:@Catharz, very funny. And yes, light speed is infinitely quick. Guess how long it takes mass to travel billions of light years travelling at (all but) light speed?

No time at all! Funny that. Billions of years still pass in the static universe, but light speed travel really is infinitely fast for those doing it.

Seriously...

DSMatticus · Post by **DSMatticus** » Sat Jul 28, 2012 1:09 pm

"I have travelled 10 light years instantly but it aged the universe 10 years" is a very weird to say "I have spent 10 years travelling 10 light years, but no time has passed for me." I don't know if you can call it incorrect, but I'm not jumping to call it correct either. It doesn't exactly seem right to say you travelled a finite distance infinitely fast only to discover that time has passed for your destination (and everything else) since you left for it.

Ted the Flayer · Post by **Ted the Flayer** » Sat Jul 28, 2012 4:52 pm

Why is it that the most back-stabbing places I have worked at are always the ones that paid the least money? Or is it just me that experiences it?

CatharzGodfoot · Post by **CatharzGodfoot** » Sat Jul 28, 2012 5:13 pm

DSMatticus wrote:"I have travelled 10 light years instantly but it aged the universe 10 years" is a very weird to say "I have spent 10 years travelling 10 light years, but no time has passed for me." I don't know if you can call it incorrect, but I'm not jumping to call it correct either. It doesn't exactly seem right to say you travelled a finite distance infinitely fast only to discover that time has passed for your destination (and everything else) since you left for it.

No. Let me put it in simple terms. The limit of y/x as x -> ∞ is 0. The limit of y/x as x -> C is y/C. In a vacuum, we know C is about 3*10^8 m/s.

So let's compare these two quantities: y/x as x->∞ m/s and y/(3*10^8) m/s.

Let's say you want to go, I don't know, 3*10^8 meters (one light second in a vacuum). The first equation is (3*10^8 m)/x as x->∞ m/s, or immeasurably little time. The second is ( 3*10^8 m)/( 3*10^8 m/s), or 1 second.

Let's change the distance it just so that we can make a rudimentary trend line.. How about we go with 9*10^15 meters this time.

First equation: (9*10^15 m)/x as x->∞ m/s. That's odd, the answer is still immeasurably close to no time at all.
Second equation: (9*10^15 m)/( 3*10^8 m/s). 3*10^7 seconds, or about a year. Wow, I guess there is a pretty big difference between infinity and a finite quantity like C!

Username17 · Post by **Username17** » Sat Jul 28, 2012 5:27 pm

Ted the Flayer wrote:Why is it that the most back-stabbing places I have worked at are always the ones that paid the least money? Or is it just me that experiences it?

The lower the stakes, the more vicious the fighting. It's called Sayre's Law, and it's a well documented phenomenon.

-Username17

Ted the Flayer · Post by **Ted the Flayer** » Sat Jul 28, 2012 10:59 pm

That makes sense.

Although I can see why that is upon reflection. Even considering that I only have a month left here at this place, I feel like a wounded animal. Maybe it would help to snarl at people..

DSMatticus · Post by **DSMatticus** » Sun Jul 29, 2012 1:45 am

CatharzGodfoot wrote:
DSMatticus wrote:"I have travelled 10 light years instantly but it aged the universe 10 years" is a very weird to say "I have spent 10 years travelling 10 light years, but no time has passed for me." I don't know if you can call it incorrect, but I'm not jumping to call it correct either. It doesn't exactly seem right to say you travelled a finite distance infinitely fast only to discover that time has passed for your destination (and everything else) since you left for it.

No. Let me put it in simple terms. The limit of y/x as x -> ∞ is 0. The limit of y/x as x -> C is y/C. In a vacuum, we know C is about 3*10^8 m/s.

So let's compare these two quantities: y/x as x->∞ m/s and y/(3*10^8) m/s.

Let's say you want to go, I don't know, 3*10^8 meters (one light second in a vacuum). The first equation is (3*10^8 m)/x as x->∞ m/s, or immeasurably little time. The second is ( 3*10^8 m)/( 3*10^8 m/s), or 1 second.

Let's change the distance it just so that we can make a rudimentary trend line.. How about we go with 9*10^15 meters this time.

First equation: (9*10^15 m)/x as x->∞ m/s. That's odd, the answer is still immeasurably close to no time at all.
Second equation: (9*10^15 m)/( 3*10^8 m/s). 3*10^7 seconds, or about a year. Wow, I guess there is a pretty big difference between infinity and a finite quantity like C!

Nothing about that is a response at all. I suspect you actually have no idea at all why Tussock said the speed of light is infinite, let alone why it might be wrong (or more appropriately: strange or misleading). That, or you're just being snarky with the simple explanation and not realizing it totally misses the point.

So, let's start off by explaining what Tussock meant: as you approach the speed of light, time dilation kicks in and time passes slower for you but not for everyone else. At the speed of light itself, the effect is complete and time stops. If you turn on your stopwatch, engage your lightspeed engine, reach your destination, turn off your lightspeed engine, and stop the stopwatch, it will read 0.00... seconds. Because for you, you arrived at exactly the same instant you left. Or to use condescendingly elementary math: the limit of d/t as t->0 is infinity, so when you naively look at your mile odometer and your stopwatch, you appear to have been travelling at infinite speeds.

Now, if you had a prearrarranged departure time, and your destination turns on the stopwatch at this prearranged departure time in order to time you, and you are 10 light-seconds away, their stopwatch will read 10 seconds when you arrive. Because the speed of light is 1 light-second per second, and something moving at the speed of light towards them will cover 10 light-seconds in 10 seconds.

The reality of why Tussock is wrong is because nobody measures time like that because it's useless and not indicative of anything; time objectively passes in the universe while you travel at c, even if no time passes for you. It deserves the same kind of groaning and eye-rolling you'd give a bad pun, because that's basically all it is; a pun on how we conceptualize time.

angelfromanotherpin · Post by **angelfromanotherpin** » Sun Jul 29, 2012 2:33 am

Nothing about special relativity makes any goddamn sense. Seriously, every time I start peeling that onion I find a new layer of batshit. Apparently due to relativity of simultaneity, two clocks can each run slow relative to the other.

what i dont even

If anyone can decipher that for me, I'd appreciate it, but I'm not holding my breath.

Username17 · Post by **Username17** » Sun Jul 29, 2012 4:49 am

angelfromanotherpin wrote:Nothing about special relativity makes any goddamn sense. Seriously, every time I start peeling that onion I find a new layer of batshit. Apparently due to relativity of simultaneity, two clocks can each run slow relative to the other.

what i dont even

If anyone can decipher that for me, I'd appreciate it, but I'm not holding my breath.

It has to do with time dilation and relative velocity. That is, if two things are moving away from each other, it is equally valid to say that one is stationary and the other is moving or that one is moving and the other is stationary. So Clock A feels its own time moving forward normally and sees Clock B hurtling through space under the weight of the time dilation that would entail, while Clock B feels its own time moving forward normally and sees Clock A, yadda yadda.

The key is that the two clocks are actually seeing light from the other clocks that is traveling a fair distance and from increasingly far "in the past" when they try to check the time the other clock is reading "right now". And in order to get the clocks back into the same reference frame you'd need to spend a whole lot of energy pushing them back together - an act that would be experienced with enough time dilation that it would undo the discrepancy between them.

-Username17

angelfromanotherpin · Post by **angelfromanotherpin** » Sun Jul 29, 2012 5:39 am

How does that cohere with the twin paradox where one object undergoes time dilation that is specifically *not* reconciled with the other?

DSMatticus · Post by **DSMatticus** » Sun Jul 29, 2012 8:16 am

Okay, so, the clock paradox you described where each clock looks at the other and says "you're running slowly?" That is the first half of the twin paradox. The twin paradox is that exact same problem, plus the round trip that brings them back together. Yes. That's right. When one twin hops on his space ship to fly away from the other twin, both twins look at eachother and go, "why is he aging slower than normal?"

Anyway, the return trip is the thing that brings the two twins back together. But it only brings simultaneity back together; it doesn't affect the actual passage of time each has experienced. So when the twins come back together, they stop seeing the other age more slowly and see the other aging at the 'correct' rate. But more time has passed for one of the twins than the other, so even if they are aging at the same rate they are not the same age.

I am not actually at all clear on what the round-trip looks like to each twin, though it is obvious they can't both keep aging slowly with respect eachother and then they end up together and one is older. I am not actually sure why the space twin is consistently older than the earth twin, since "everything is relative" is supposed to be the big deal in special relativity, but there is some kind of asymmetry (the turn around) the twins experience which makes them distinguishable from one another supposably.

Some notes:
Simultaneity is the same for any two observers that have zero relative velocity. Otherwise, things which are moving at different speeds experience simultaneity differently. The twins don't actually have to be brought next to eachother, they just have to be brought to zero relative velocity, even if they are lots of light years away. (This also stops the time dilation).

Neither time dilation nor relativity of simultaneity have anything to do with signal propagation. It's not an effect caused by the delay in receiving information from distant locations. Even accounting for signal delay, time is passing differently. If Space Twin sends a radio beep back every second, Earth Twin will find that the time between those radio beeps is larger than [(one second) + (the time it took for light to cover the distance space twin travelled since the last beep)].

tussock · Post by **tussock** » Sun Jul 29, 2012 12:43 pm

The twin paradox, and angelfromanotherpin's Q, are fairly easy.

When you move at constant velocities relative to each other, each other's clocks don't just "appear" to run slowly, they do run slowly. Both of them. Yes. But when you accelerate toward the other at a distance you speed up the other one's clock far more dramatically. Both age slower that the other on the way out, the earth twin ages much faster during the turn around, and then both age slower than the other again on the way back in.

They can't agree about when the turnaround occurred because simultaneity is a lie, they can only agree about how much time has passed for the other when they arrive back in the same place.

Same with (very near) light speed jumps. If you could get up to speed extremely fast without all those inertia issues, the reason time seems to pass for the outside world as you travel at (very near) infinite speeds toward some distant place is because you put all of space ahead of you into your future by the correct amount by accelerating toward it at a distance (and only slowing down again when closer, which also puts home base into your future by the same amount, you being the only one to stay young).

And those clocks way ahead of you really do run faster as you accelerate toward them. GPS has to account for the ground accelerating in the gravity well toward them. It's not an appearance of strangeness, it is genuinely strange.