trench on December 07, 2011, 09:09:36 pm
So it wouldn't really look like there is no time and no space, it would just look like there's only one point of space and that time has stopped moving.

Which, come to think of it, I imagine would be quite similar to viewing the universe from the outside and very far away.

trench on December 08, 2011, 12:47:51 am
Yes, given certain assumptions about how the universe works, that might be a reasonable conclusion. Other assumptions, however, result in different conclusions.

Sure, if we assume it must go through this brane or doesn't use a worm hole or other mechanism that side-steps this universe. As I said, different assumptions result in different outcomes.

You're missing the point, unless what you mean to say is that special relativity is an assumption about how the universe works. If we can agree that it is, in fact, established scientific fact and really is the way the universe works, so called "instantaneous" communication does, by necessity, imply time-traveling communication, at least at very high velocities (or very large distances), because there is no universal "now". It doesn't matter if the signal "side-steps the universe" (which, by the way, doesn't make sense), as long as it ends up "inside" the universe or whatever would be the parallel to the thing you said.

Let's start with the basics. Let's say you and I are moving relative to each other at some significant fraction of the speed of light, and I decide I want to signal you, and that upon receiving that signal, you decide to signal back. If we call event a me sending the signal, b you receiving it and transmitting a return to me, and c my reception of your signal, than basically a leads to b leads to c. Because there's a high relative velocity involved, the time between them would be different in my perception than in yours, but as long as our relative velocity is less than the speed of light, the events will always happen in that order.

But now let's assume the communication is instantaneous. Since we're moving relative to each other, from my point of view, time is moving more slowly for you than it is for me, with the result that if I send the signal at my local time t1, you will receive the signal at your own local time t' < t1. Note that it really, really does not matter how the signal gets there, just that it does, and that special relatively is a real thing.

Now, let's keep focusing on event a, but from your point of view now. Since, from your point of view, my time is moving more slowly than your time, I will not send the signal until some time t'' > t1.

Now we have, from your point of view, event b at t', and event a at t''. Using some very basic arithmetic, if t' < t1 and t1 < t'', it becomes clear that t' < t'', and so you receive the signal before I send it. This, for most people, would constitute a time-traveling communication. One very important ramification of this, in case you're not convinced, is that from my point of view again, event c will precede events a and b (which from my point of view are simultaneous). That it to say, I will receive your response to my signal before I send the signal in the first place.

To clarify the chain of events in this case:
From my point of view, c -> a,b
From your point of view b,c -> a

And that all happens regardless of how the signal get's there, just that it does.

trench on December 08, 2011, 12:59:59 am
Hmm. Use thousands of small ships in a really big elliptical orbit.  Have two sets orbiting in opposite directions. Each one has connections to all of the others going in the opposite direction, but will only send data to the one passing closest.

Time gain is smaller, but a lot of the pairs have a usable time gain, and you can daisy-chain your signal as many times as you need to to get the time length you want.

If each one has enough bandwidth, you can re-daisy chain repeatedly to get a signal sent from the time in the future when the system is shut down, to the time in the past when the system was started up.

Finding a way to prioritize use will be a problem ... you may think your day ahead stock quotes are more important that the battered signal concerning 1000km wide Asteroid DA1950 striking the Earth in circa 2800 AD ...

I'm not sure this would work, for a couple of reasons. On a practical level, the ships would require... a lot of bandwidth. Possibly an infinite amount of bandwidth, which I don't think the tanglenet supplies.

Well, ok, not an infinite amount of bandwidth, but certainly the bandwidth of each ship would have to be relative to the amount of time the system exists. Each ship would have to be able to both transmit and receive every single message sent throughout the lifetime of the program all at once.

On a mathematical level, you're talking about non-inertial reference frames, about which special relativity makes no guarantees. I'm not certain, not having actually worked it out, but I would bet that the daisy-chaining through time wouldn't actually work, and trying to do it would only yield as much time gain as a single transmission, minus some overhead to handle the signal.

mellyrn on December 08, 2011, 06:47:52 am
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if we introduce general relativity when you have not altogether understood special relativity, that will confuse you even more.

True, that!

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As for how close it's possible to get to being truly motionless, it isn't. That is to say, there's no such thing as "truly motionless", because the whole point of special relativity is that you always have to ask "relative to what?" [....]

It's tempting to suggest that since the universe is probably finite and probably symmetrical ... that there is a theoretically identifiable center of the universe, relative to which you could theoretically make yourself motionless.

I get that.  I'm inclined to invoke a demon -- The Demon At The Center Of The Universe.

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It's not really that for them time and space don't exist, it's that they don't perceive them. [....]  So it wouldn't really look like there is no time and no space, it would just look like there's only one point of space and that time has stopped moving.

Does that help?

Not at all.  I can't see the difference between "don't exist for them" and "can't be perceived by them".  It's not like, say, radioactivity, which couldn't be perceived by humans until we developed certain technology -- it's that there is no way at all, even in theory, for a photon to become aware of anything like "space" or "time".  "Only one point of space" leaves nothing outside that point for it to be compared to (and are we talking a Euclidean point, which has no dimensionality?), and the same for nonmoving time.  There is no space for a photon to explore; there is no past to look back into nor future to wonder about.  It's like, if everything -- absolutely everything -- is black, there is no way to know that it is black because there can be no concept of white or even green.

Only a demon ;) could say, "It's black."

In this space-time continuum of ours, as we currently understand it, it is possible for something to exist for which neither space nor time is a real thing, nor even a theoretical thing.  Sooo, what's real?

Interestingly, Parmenides (ca. 500 BCE) proved, logically proved, that change is impossible.  To the best of my knowledge, no one has ever successfully disproved him; it just gets ignored as a paradox, since, whatever logic might say, we do have to deal with change.  Seems that, for photons at least, he was right.  Heh.

SandySandfort on December 08, 2011, 08:23:58 am
You're missing the point, unless what you mean to say is that special relativity is an assumption about how the universe works. If we can agree that it is, in fact, established scientific fact and really is the way the universe works, so called "instantaneous" communication does, by necessity, imply time-traveling communication, at least at very high velocities (or very large distances), because there is no universal "now". It doesn't matter if the signal "side-steps the universe" (which, by the way, doesn't make sense), as long as it ends up "inside" the universe or whatever would be the parallel to the thing you said.

What if your perceived or hypothetical "relative velocity" is zero as measured through the frame of reference of--for want of a better word--hyperspace?

Newtonian physics is an almost perfect first approximation of how things work, at less than relativistic speeds, but we didn't know that until science had advanced to the point where we could discover otherwise. I think it is the height of arrogance to assume that special relativity is the Ultimate Description of Everything, and that there are no work-arounds, yet to be discovered. 

Of course, my tanglenet hand-waving was created to allow for intriguing plot elements. However, as far as I know, no one has ever considered that entangled particles may not be more than one particle at all. Perhaps they are just two aspects of the same particle that are separated by space and relative motion only as seen from the only space-time we can currently perceive. This is more hand-waving, of course, since no evidence exists for speeds greater than c (with the possible exception of the CERN anomaly) much less instantaneous travel, but as Carl Sagan said "Absence of evidence is not evidence of absence"

Bottom line, though, EFT is fiction. The tanglenet is a literary device. Deal with it.

macsnafu on December 08, 2011, 09:04:05 am


Not at all.  I can't see the difference between "don't exist for them" and "can't be perceived by them".  It's not like, say, radioactivity, which couldn't be perceived by humans until we developed certain technology -- it's that there is no way at all, even in theory, for a photon to become aware of anything like "space" or "time".  "Only one point of space" leaves nothing outside that point for it to be compared to (and are we talking a Euclidean point, which has no dimensionality?), and the same for nonmoving time.  There is no space for a photon to explore; there is no past to look back into nor future to wonder about.  It's like, if everything -- absolutely everything -- is black, there is no way to know that it is black because there can be no concept of white or even green.

Only a demon ;) could say, "It's black."

In this space-time continuum of ours, as we currently understand it, it is possible for something to exist for which neither space nor time is a real thing, nor even a theoretical thing.  Sooo, what's real?

Interestingly, Parmenides (ca. 500 BCE) proved, logically proved, that change is impossible.  To the best of my knowledge, no one has ever successfully disproved him; it just gets ignored as a paradox, since, whatever logic might say, we do have to deal with change.  Seems that, for photons at least, he was right.  Heh.


Which just goes to show that it is possible to make constructs that are logical, but nonetheless void of any relationship with reality.
I love mankind.  It's PEOPLE I can't stand!  - Linus Van Pelt.

macsnafu on December 08, 2011, 09:11:01 am
Newtonian physics is an almost perfect first approximation of how things work, at less than relativistic speeds, but we didn't know that until science had advanced to the point where we could discover otherwise. I think it is the height of arrogance to assume that special relativity is the Ultimate Description of Everything, and that there are no work-arounds, yet to be discovered. 

As I like to say, Newtonian physics didn't suddenly stop working when Einstein came along.  Newtonian physics still works as well today as it did when Newton discovered it. Einstein just came up with a better, more precise theory.

I also find it fascinating how strange things are at the extremes, but how in the middle all this strange stuff makes up what we perceive to be the ordinary, everyday world.

I love mankind.  It's PEOPLE I can't stand!  - Linus Van Pelt.

mellyrn on December 08, 2011, 10:51:19 am
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Which just goes to show that it is possible to make constructs that are logical, but nonetheless void of any relationship with reality.

It says a lot about what it means to think, that we can do that.

It's all constructs anyway.  "Red" is how your neurons construct the interaction of certain wavelengths with certain biophotochemicals.  "I" am a construct whose boundaries are highly arbitrary -- at what point does the O2 I inhale cease to be "other" and become "me"?  No one would draw a human figure without a head and say, "That's a man", because a "man" with no head is already-decaying protoplasm and not "a man" at all; yet a man without a universe is just as dead.  Yet I construct, or, better, abstract "myself" as being thus-and-not-that.

I once read of a physicist (well-respected, according to the mainstream popularized-science mag in question) who reconciled QM math with relativity math by doing away with the concept of time entirely.  His physics makes (made?) internally-consistent sense, and applied both subatomically and cosmologically; and yet the IRS can still charge me interest.

So we can also make constructs that are logical and have some, even substantial and useful, relationship with reality, and at the same time make no sense at all. 

It's the great cosmic joke!

Killydd on December 08, 2011, 12:22:00 pm
Macsnafu, if we lived at one of those extremes, we'd consider it normal, then that it went into one strangeness, then another one after that. 

Sandy, it may be that there are workarounds, and that those workarounds in the end mean time travel, just in such a way that the universe doesn't collapse into meaninglessness.  Also, it's simply a cross that sci-fi writers bear to have a "useful plot element" criticized just because it is impossible or inconsistent with current understandings.  Also, the CERN anomaly turned out to be just a measurement error that people jumped on before it was confirmed or refuted just because it would have been such a big story that they wanted to be the first to report it.
As for velocity being zero through some hyperspace but not real space, the proof starts getting very ugly.  When quantum mechanically finding the chance of a particle arriving somewhere, you don't just take the actual path.  You take the weighted sum of all possible(and impossible) paths to get from one point in space-time to another.  going through some hyperspace wormhole is another path that just has to be accounted for normally, so we should see it with our ongoing experiments in relativity anyway.

Mellyrn, Newton resolved that paradox when he invented calculus.  We now know how to divide by zero, at least under special circumstances, which include finding an instantaneous rate of change. 

mellyrn on December 08, 2011, 01:06:38 pm
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Mellyrn, Newton resolved that paradox

I'm sorry; which one?  Parmenides' paradox, or the incompatibility of QM math and relativity math, or the non-spacetime universe of Photon ("There can be only one") vs our spacetime one?  Not that I can apply calculus to any of them anyway.

I'm really not wanting to be a butthead here; I'm not trying to not-get it, so I think I'll drop out before I'm too exasperating.  I do thank you all for your efforts.

Though it would be cool if my confusion weren't just my personal inability but sprang from some real conflict within current theory, and one of you, beating his head on his keyboard in vexation with me, suddenly had a great Aha! and launched the next revolution in physics.  Unlikely, but cool.

Killydd on December 09, 2011, 01:31:18 am
Mellyrn, it's not just you.  I was referring to Parmenides paradox though, as Newton was before the other ones came to our attention.  Coming to grips with quantum mechanics or the odd parts of relativity are both things that almost everyone has difficulty with.  Combining the two is still beyond the edge of current physics, unfortunately, although there are efforts.

sam on December 09, 2011, 03:50:11 am
What if your perceived or hypothetical "relative velocity" is zero as measured through the frame of reference of--for want of a better word--hyperspace?

This makes no sense:  Relative velocity is real, it is not "perceived" or "hypothetical".  It is not difficult to have one thing moving relative to another, and if one thing is moving relative to another, its relative motion is not zero in any frame of reference.

mellyrn on December 09, 2011, 06:43:57 am
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Mellyrn, it's not just you.

Thank you; I take that kindly.

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I was referring to Parmenides paradox

Ah!  And, on further reflection, I kind of see what you mean about Newton and calculus.  Not sure if you'd want to discuss it further, though.

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Combining the two is still beyond the edge of current physics

Coming to see two (quite separate and distinct) islands as two peaks of the same mountain takes a fairly radical shift in perspective (a transparent ocean!)  If it's being so hard to combine QM and relativity, that rather suggests that there is some still more fundamental principle as yet undiscovered -- e.g. the aforementioned guy who reconciled them by eliminating the concept of time altogether (hey, it was "Discover" magazine, late '90s; they did the best they could).  Time is in many ways a problematic notion and if it proves to be an illusion, that would suit Parmenides, too.

Killydd on December 09, 2011, 01:34:28 pm
Central to the idea of an "instantaneous rate of change" is the limit:  certain functions have spots in them where you can't evaluate them because of a "divide by zero" error.  However, if you take the limit as you approach that spot, it MIGHT converge to a certain point.   For example, y=x/x.  You might just simplify it to say y=1, but when x=0, you'd get a "divide by zero" error.  However, the limit as x approaches 0 is still 1.  No matter how small x gets, positive or negative, the equations still evaluates to y=1, as long as x=/=0. 

A little more complicated, take what happens when you drop a ball.  the position y=-.5gt*t.  To find it's speed(okay, velocity) y'= the limit as h approaches zero of (y(t)-y(t-h))/(t-(t-h), or just the change in height divided by the change in time, as these changes approach zero.  expand and you get ((-.5g)(t*t)-(-.5g)(t-h)(t-h))/h.  factor out to get (-.5g)(t*t-t*t+2th-h*h)/h.  simplify to reach (-.5g)(2th-h*h)/h, and since we're still inside of that big limit structure, we can pull an h out also for (-.5g)(2t-h).  Now take the actual limit, since h is only at the top it can be zero, to get a speed of -gt. 

Honestly, Parmenides problem was that he believed in a smallest positive number, and this approach requires that no such thing exist.

If that was a little fast, realize that this is probably an entire lecture's worth of 200 level college math that liberal arts majors don't even take. 

sam on December 09, 2011, 06:31:37 pm
If it's being so hard to combine QM and relativity, that rather suggests that there is some still more fundamental principle as yet undiscovered

Spontaneous symmetry breaking and cosmic inflation are both indicators that on a small scale, space time has a complex ground state (ground state in the sense of local energy minimum, rather than global energy minimum) with a dimensionality different from the apparent large scale dimensionality.

Since we cannot know that ground state, failure to quantize general relativity is unsurprising.

These two factors suggest that originally there was a rapidly inflating universe, in which the state of vacuum was simple, but relatively high energy, and the laws of physics were also simple.  This cascaded into a series of ever lower energy, but ever more complex energy minima, producing ever more regions of ever more complex physics and ever slower inflation, the most recent such collapse being the explosion that we perceive as the big bang.

In each of the vacuum collapses leading to our present universe, there were a multitude of different ways the cookie could crumble, and indeed a multitude of ways the cookie did crumble, but because of cosmic inflation, we can only see one particular outcome of many - an outcome where the laws of physics happen to be compatible with intelligent life.

This leads to the prediction that at a very small scale, spacetime has a complicated and messy high dimensional structure, effectively the rubble of all the preceding vacuum collapses, hence, hard to quantize.
« Last Edit: December 09, 2011, 09:10:59 pm by sam »

 

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