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[Mjolnir]

Also, if I'm not mistaken, changes in gravity propagate at the speed of light. I know nobody has yet found a graviton, but I think someone was able to measure the lag at least.

It is indeed. However, gravitons are an element of quantum field theories that attempt to incorporate gravity, they're not part of GR.

There were attempts to measure the propagation of gravity by watching the lensing of background stars caused by Jupiter's gravity field, but there was some dispute about whether the method was valid. Better evidence comes from binary pulsars, where orbits decay just as GR predicts they would due to emission of gravitational radiation.

[bunnyboy]

...

For all space time physist here. Somehow physics of was much easier to understand.

Could he really not see the problem? "Where is the sun?" asked Parson in exasperation.

Sizemore squinted at him. "In that hex? Four minutes further along in the sky."

"It jumps backwards when I enter the hex?!"

"Of course! To you," said Sizemore. "Because you traveled and were observed from that hex. If you weren't observed, you would find the sun in the same position as the previous hex."

"Ridonkulous!"

[TrashMan]

It's not just acceleration but also relative velocity, there's no medium involved, and time dilation isn't an issue of perception. Two people can take different paths through spacetime and meet again after experiencing different amounts of time.

This I understand. What I never understood is that "sending messages bask in time". How exactly?
At any point time passes. It ALWAYS goes forward - it might go at different rates, but it always goes forward.

I blame mathematics with some strange paradoxes and stuff. After all, there's plenty of stuff in math that don't exit in real life (like imaginary numbers)

[Mjolnir]

This I understand. What I never understood is that "sending messages bask in time". How exactly?
At any point time passes. It ALWAYS goes forward - it might go at different rates, but it always goes forward.

As long as nothing transmits information faster than light, this is so. Messages traveling at c or slower can never go back in time...people will disagree about whether things happened at the same time or which happened first, but they'll never receive anything from their own future.

I blame mathematics with some strange paradoxes and stuff. After all, there's plenty of stuff in math that don't exit in real life (like imaginary numbers)

And real numbers actually exist, do they?

Imaginary numbers are as "real" as the natural numbers, integers, real numbers, rationals, complex numbers, quaternions, tensors, and so on. They're all concepts that are defined, described, and related by the same basic framework of logic. And imaginary numbers are extremely useful in describing reality.

[Ktrain]

And real numbers actually exist, do they?

Imaginary numbers are as "real" as the natural numbers, integers, real numbers, rationals, complex numbers, quaternions, tensors, and so on. They're all concepts that are defined, described, and related by the same basic framework of logic. And imaginary numbers are extremely useful in describing reality.[/quote]

Question: Do numbers reflect a fundamental reality/truth of the universe or are they artificial constructs used by man to help us understand an inherently confusing and non-rational universe?

[Mjolnir]

Question: Do numbers reflect a fundamental reality/truth of the universe or are they artificial constructs used by man to help us understand an inherently confusing and non-rational universe?

If the universe is fundamentally irrational, it's doing an oddly good job of pretending to follow rules. Since there's no way to tell whether this is just by chance or not, I consider that a rather worthless question.

Ask again when the universe stops following rules. Until then, I'm fine with using math to describe and predict it.

[Ktrain]

That last last sentence proceeds from the assumption that induction can readily distill the rules of the universe, but it could very well be our own human perspective which is ordering and projecting reason onto nothing more than a series of coincidences. The rules might fit in our heads but not inherently part of the external reality; they are merely tools Maybe I'm just being an epistemological troll.

[icekatze]

hi hi

That kind of meta-reality would be intriguing if it ever had any bearing on anything. Yes, we could all be brains in a jar somewhere, but since nothing we can do or observe has ever had any effect on that or vice versa, it isn't really pertinent to our current existence, whatever that may be.

The value of science lies in its ability to predict future events, something it does quite well. If you want to conflate coincidence and consistency thats all well and good for you, but I don't really see the point.

Edit: Also, this little bit of news is surprisingly relevant to the discussion at hand.

[Mjolnir]

That last last sentence proceeds from the assumption that induction can readily distill the rules of the universe,

No, the assumption is that it can achieve successively more accurate mathematical models that can be applied to predict the universe. And that sentence also proceeds through a global network of vastly complex electronic machines deeply dependent on a wide variety of different technologies that all depend in extreme detail on the success of this approach. And it got where I wanted it to go.

but it could very well be our own human perspective which is ordering and projecting reason onto nothing more than a series of coincidences. The rules might fit in our heads but not inherently part of the external reality; they are merely tools :D Maybe I'm just being an epistemological troll.

Thoroughly useless blather. Unprovable, unfalsifiable, and completely irrelevant, and rather insulting to scientists and engineers everywhere and throughout all history.

[Ktrain]

Mjolnir, perhaps you are reading more into the original query than there actually is. It was only in reference to your assertion that imaginary numbers are real. I only took your point one step further and posited the realist and skeptics positions. Let me reiterate: Are numbers real in that they are fundamental truths of our reality or are they real in the sense that we define them as such?

Metaphysical assumptions underlie human understanding, even science and math have metaphysical foundations.

My only poke at science is contrasting inductive and deductive reasoning. Induction cannot prove anything; it can only give evidence for or against a certain position/assumption. Proofs are in the realm of deductive reasoning. Science relies an inductive reasoning to support theories, but it relies on the metaphysical assumptions that a) reality is rationally discernible and b) phenomena behave in a consistent repeatable manner given certain conditions. Studying correlation allows humans to make inferences about causation, but it does not allow us to prove causation.

Thoroughly useless blather. Unprovable, unfalsifiable, and completely irrelevant, and rather insulting to scientists and engineers everywhere and throughout all history.

The skeptics position is neither an insult or affront to science, it is merely a counterbalance to the realist. To assume that it is useless and insulting disregards role skepticism has played in the historical formation of scientific disciplines (e.g.: David Hume). There is nothing offensive about thinking that the order is merely in our heads or that it is inherently part of the external system. In my previous post I took neither position was merely positing an alternative position as a digression from the original math comment.

[Mjolnir]

Mjolnir, perhaps you are reading more into the original query than there actually is. It was only in reference to your assertion that imaginary numbers are real.

I never asserted this.

The skeptics position is neither an insult or affront to science, it is merely a counterbalance to the realist. To assume that it is useless and insulting disregards role skepticism has played in the historical formation of scientific disciplines (e.g.: David Hume). There is nothing offensive about thinking that the order is merely in our heads or that it is inherently part of the external system. In my previous post I took neither position was merely positing an alternative position as a digression from the original math comment.

Implying that all that scientists and engineers have achieved is an illusion resulting from coincidence is insulting. And it is literally without any use whatsoever, leading to no conclusions, mostly serving as a defense of ignorance on the grounds that "those scientists don't really know anything anyway". It's pseudo-intellectual hogwash.

The fact is that science has been extremely successful in producing detailed, accurate descriptions of reality. The scientific approach has given us a deep understanding of the universe, one that is constantly improving, and it's given us countless technological wonders. The naysayers claiming it could all be coincidence have given us...nothing but voluminous ill-reasoned blather.

[Cy83r]

Everything that scientists and engineers have achieved is an illusion resulting from coincidence, but that quirk is statistical rather than philosophical.

As for time travel, there's probably some sort of rule in there like the conservation of energy/mass/information (there'd have to be some sort of physical law like that to prevent time travelers from dumping all of their wars and/or bad stocks into our present, right?) that would make any practical attempt at traveling back something like reprogramming spacetime itself, which, if what I've gleaned from some of these books I've read by the Big Names in Science, might be more or less another creation event a la the Big Bang.

[Arioch]

We know that time travel isn't possible because if it was, there would be time travelers all over the place.

The same way that we know FTL travel isn't possible.

[Ktrain]

The same way that we know FTL travel isn't possible.

This came up in one of my meetings with the local astronomic society last year. Perhaps all civilizations/species that are advanced enough to achieve FTL travel have no interest talking with a primitive species such as humanity. Kind of like how it would be interesting for a human to communicate with a Chimpanzee... for like 10 minutes. Imagine a vastly more evolved and developed being, to them the way in which man engages reality may be too base and simple to gain their interest.

Everything that scientists and engineers have achieved is an illusion resulting from coincidence, but that quirk is statistical rather than philosophical.

Bingo.

Also Mjolnir, you did say

Imaginary numbers are as "real" as the natural numbers, integers, real numbers, rationals, complex numbers, quaternions, tensors, and so on. They're all concepts that are defined, described, and related by the same basic framework of logic. And imaginary numbers are extremely useful in describing reality.

You assume I am attacking science, but you misdirect your attention. I am merely commenting on the nature of knowledge and one of the fundamental metaphysical debates. Are numbers and math human constructs and tools created to understand phenomena or are they inherently part of the phenomena around us and abstracted from our observations. Nothing in either case negates or challenges science, neither belief challenges the usefulness of mathematics. I have studied under mathematicians who held the opinion that numbers are human constructs and ones who have felt numbers are inherent in the universe.

[Cy83r]

We know that time travel isn't possible because if it was, there would be time travelers all over the place.

The same way that we know FTL travel isn't possible.

Right, at least in the first issue, after the first time traveler you start getting time travelers who believe we shouldn't be time traveling and then some of the pro-traveler travelers organize after having their causal histories assaulted by militant anti-traveler travelers and then it just snowballs into a time war against terror in the seven-hundredth iteration branch-history. And you know once they start building time-bases, they'll never go back home, so the natives steal the time-travelers' tech and fight an insurgency to get all of the damn future persons that technically don't exist yet out of their timespace. AND THEN they bring in the reinforcements and the supplies necessary and it just spirals completely out of any semblance of control. After that, it's only a matter of time before the universe gets tired of being puckered by repeated timeholes and resets the local existence.

It's just silly.

Compared to that, using hyperspacetime and particles with imaginary mass to exceed the lightspeed barrier without violating temporal continuity is child's play.

[Mjolnir]

Also Mjolnir, you did say

Imaginary numbers are as "real" as the natural numbers, integers, real numbers, rationals, complex numbers, quaternions, tensors, and so on. They're all concepts that are defined, described, and related by the same basic framework of logic. And imaginary numbers are extremely useful in describing reality.

Yes, I did say that. And I meant exactly what I said. Not what you claimed I said.

Compared to that, using hyperspacetime and particles with imaginary mass to exceed the lightspeed barrier without violating temporal continuity is child's play.

Except it isn't.
FTL, relativity, causality...pick any two. You can't take all three, as each combination of two excludes the third. And to make it easier, one's already been picked for you...relativity's not optional, the parts of it that make FTL and causality incompatible have been experimentally verified as being real effects. You get FTL or you get causality, you can not have both. And we do appear to have causality, and a distinct lack of both time travelers and alien visitors...

[JeroOfBaconGrease]

I've heard it suggested that were it possible to exceed the speed of light that the power requirements would be so enormous as to require the full backing of the civilization's capabilities. Then again, maybe the only reason no aliens have visited is they haven't started getting our oldest radio transmissions yet, & the time travelers are too busy with more cosmically relevant time periods, like the beginning of the universe, or even just the Solar System.

It took me a while to come up with something I thought might be slightly relevant here.

[Cy83r]

I've heard it suggested that were it possible to exceed the speed of light that the power requirements would be so enormous as to require the full backing of the civilization's capabilities. Then again, maybe the only reason no aliens have visited is they haven't started getting our oldest radio transmissions yet, & the time travelers are too busy with more cosmically relevant time periods, like the beginning of the universe, or even just the Solar System.

It took me a while to come up with something I thought might be slightly relevant here.

Actually, the lightspeed barrier is to conventional acceleration as zero kelvin is to advanced refrigeration research; the energy required per-unit-change increases at a geometric rate the closer you get to 1c or 0K. So, unless you have wormholes cutting down the distance or some fancy-as-new particle field generator tricking physics into thinking you weigh less than zero, you can even get to lightspeed or any pertinent fraction thereof without significant time allotted to slowing down again which makes going that fast and dragging along enough armor to survive any deep space microdebris impacts fiscally prohibitive for any civilisation.

And, frankly, I'm beginning to get a little irritated, Mjolnir; physics as we know it can only postulate what wormholes or FTL particles like tachyons might do let alone what sort of timey-whimey effects they have on people using those phenomenon (mathematically postulated phenomenon in the case of tachyons) for travel purposes. So I'll have none of your party poopery in saying that the math says 'it doesn't work that way'. Anyone remember when Hawking had to retract his claim that Black Holes are, and I heavily paraphrase here, "impossible because they destroy information"? at which point somebody suggested that hawking radiation (it was named after the guy, for Pete's sake) might have a connection to what the black hole eats and the man himself pretty much said, with all the synthesized authority he could muster "yeah, you might be onto something".

Human science isn't perfect, hell, that's the entire point of the "scientific process"; running with what seems to work in a repeatable fashion until some yokel plumber comes up with a better definition of "that stuff over there" and addresses problems with the previous solution that weren't seen until several decades after everybody said "it seems to work, that's good enough". A lot of people seem to forget that science only ever says "this is good enough for now" not "this is it, forever, period".

So, in conclusion: dammit, let me think we at least have a chance at it until the hard numbers get back in the next several decades! Psychic powers have been dead and buried for almost the last two decades, don't take away my FTL drives just yet, we aren't even on Mars.

[Trantor]

A lot of people seem to forget that science only ever says "this is good enough for now" not "this is it, forever, period".

So, in conclusion: dammit, let me think we at least have a chance at it until the hard numbers get back in the next several decades! Psychic powers have been dead and buried for almost the last two decades, don't take away my FTL drives just yet, we aren't even on Mars.

Exactly, as long as there´s no "terminal" or "concluding" world formula, there´s still a lot to discover. On (nearly) every field.

[NOMAD]

A lot of people seem to forget that science only ever says "this is good enough for now" not "this is it, forever, period".

So, in conclusion: dammit, let me think we at least have a chance at it until the hard numbers get back in the next several decades! Psychic powers have been dead and buried for almost the last two decades, don't take away my FTL drives just yet, we aren't even on Mars.

Exactly, as long as there´s no "terminal" or "concluding" world formula, there´s still a lot to discover. On (nearly) every field.

hehe, I really hope Dec 21, 2012 doesn't happen. Looking forward to seeing what is coming next.