TBRMInsanity wrote:

You mention that some gates may take you back in time. Does this mean you could theoretically travel back to when the Iktomi were still alive? Or before the Fall?

Theoretically. Thanks to relativity any FTL space transport is also a potential time transport. However, I don't think the gates are very useful for this: they might have programmed or practical limitations (like a few pre-set, remote targets not moving with much velocity relative to each other). I would bet that any group controlling a gate would be spending enormous resources trying to figure out if there was any time travel potential in them. The rewards of success would be enormous, so even a remote chance would make it worthwhile.

Decivre wrote:

I still disagree with this possibility, for the most part. The Pandora gates to me sound like they utilize a controllable form of [url=http://en.wikipedia.org/wiki/Faster-than-light#Space-time_distortion]spa... distortion[/url], which creates awormhole. This doesn't exceed the speed of light locally, and therefore doesn't allow for time travel at all.

Nononono! That things are locally fine doesn't prevent time travel. If you can get to a event outside your lightcone - *no matter how* - there are frames of reference where you are now arbitrarily far in the future or past relative to your origin. And if you can get back into the lightcone, then you have time travel. http://sheol.org/throopw/tachyon-pistols.html http://www.theculture.org/rich/sharpblue/archives/000089.html http://www.physicsguy.com/ftl/html/FTL_part4.html#chap:unsolvableparadoxes http://stason.org/TULARC/education-books/startrek-relativity-FTL/8-2-How... Gott, J. Richard (2002). Time Travel in Einstein's Universe (or essentially any textbook on special relativity) http://pdf.aiaa.org/preview/CDReadyMJPC2004_946/PV2004_3699.pdf As Morris and Thorne pointed out in their classic 1988 paper on wormholes, they do imply the possibility of time travel: http://www.physics.uofl.edu/wkomp/teaching/spring2006/589/final/wormhole... A fixed network of gates, working in whatever way their designers planned, can however maintain causality by allowing some but not other trips. See for example this essay about "wormhole empires": http://www.aleph.se/Trans/Tech/Space-Time/wormholes.html But such a network would almost certainly (if it was large) put some locations in the noticeably far future, even if they cannot be used for time travel.

Decivre wrote:

Of course, the theory behind wormholes does supposedly allow a wormhole to be designed so as to be linked to a specific point in spacetime ahead of its own existence. If the ETI created a specific gate that was linked to Pandora gates exactly 1000 years in the future, you would theoretically be able to use currently existing Pandora gates to travel exactly 1000 years in the past through to that specific gate. However, travelling back through that gate would only send you to any other gate exactly 1000 years into the future from that moment in time again.

Good point. Pandora Gates must connect to other Pandora Gates, so if the TITANs didn't have access to the past before, they still won't, and so can't build a Pandora gate then to connect to. But yes, theoretically you could travel to the future, or up to 10 years in the past. However, that begs the question... How did the TITANs manage to build a Pandora Gate on an exoplanet.... And if they didn't, who did? The telecope idea is fantastic, and I hadn't even considered that. Of course, to be effective it hinges on the quantum entanglement bit, or otherwise transporting information faster than light, which bothers me.

Arenamontanus wrote:

This is why you should be bothered by any kind of FTL: 1. My first fork is logged onto the Martian stock market, transmitting the stock prices "simultaneously" by FTL to my second fork over at Extropia. 2. Close to Extropia my third fork sits in a spaceship that moves very rapidly. As it passes outside Extropia it receives a copy of the message from my second fork via a laser. 3. My third fork sends the message by FTL "simultaneously" (in his own reference frame) to my fourth fork, who happens to be in another fast spaceship moving past Mars in the same direction. 4. My fourth fork sends the message to my first fork, using normal laser communications. 5. If I have arranged things like in the diagrams on http://www.theculture.org/rich/sharpblue/archives/000089.html then the message arrives before my first fork sent it, and indeed before the stock market has reached the position described. My first fork uses this to invest. 6. Profit! Note that the spaceships mentioned do not have to be big, ultrarelativistic things. It is enough that I get a temporal difference of a fraction of a second for me to make huge amount of money (consider current high frequency trading). That can be done using ships moving at merely 2-3% of light-speed, a few thousand km/s. That is definitely doable with EP courier ships. Not cheap, but being able to predict the whole stock market is likely worth much more. This is time communication using only transhuman technology, not a single gate in sight. Given how economics works, if it can be done then many hypercorps will be doing it right now.

Or special relativity needs revision when it concerns the relationship between time and space, which is also a possibility when you consider that it is impossible according to special relativity to observe the relativistic difference between two different objects in spacetime (if you did so successfully, you would already be going faster than light). It could also be possible that time dilation is a local event, and that the perceived non-change in the speed of light is due solely to the local effect of them slowing at higher speeds. This is inherent in one of the primary assumptions of special relativity. The STR assumes that time is not a constant, but also declares this impossible to prove because of the speed of light. In effect, we now have two concepts butting heads against each other. Chances are that one of the two is, in fact, not true: either FTL is absolutely impossible (which doesn't seem a possibility since quantum entanglement already proves that brownian motion can occur in two places at once and violates the limitations of light), or time is a constant and dilation is a local occurrence.

Decivre wrote:

Or special relativity needs revision when it concerns the relationship between time and space, which is also a possibility when you consider that it is impossible according to special relativity to observe the relativistic difference between two different objects in spacetime (if you did so successfully, you would already be going faster than light). It could also be possible that time dilation is a local event, and that the perceived non-change in the speed of light is due solely to the local effect of them slowing at higher speeds. This is inherent in one of the primary assumptions of special relativity. The STR assumes that time is not a constant, but also declares this impossible to prove because of the speed of light. In effect, we now have two concepts butting heads against each other. Chances are that one of the two is, in fact, not true: either FTL is absolutely impossible (which doesn't seem a possibility since quantum entanglement already proves that brownian motion can occur in two places at once and violates the limitations of light), or time is a constant and dilation is a local occurrence.

Huh? The above paragraphs do not seem to make sense. Local time dilation? Time is not a constant? Brownian motion as FTL?! It seems that there are words missing, words that are needed to give sense to what you are writing. If you want to revise relativity you at least need a reason for it. How much special relativity do you know? In my example I was using entirely vanilla Lorenz transformations. No accelerations, no long distance communication, the FTL signal assumed to be "instantaneous" in the frame where it was sent/received. It is a totally standard textbook exercise and the result is completely unsurprising.

But particle spin still doesn't strictly speaking break the rule of FTL, because particle spin can't be intentionally controlled - it always operates within the Uncertainty Principle. That's why we won't be able to transmit information via quantum entanglement.

After reading some of Stephen Hawkin's work, I got thinking, couldn't time travel work if you can guarantee that the entry and exit points are in different places (thus preventing radiation feedback)? That way you could have time travel through a Gate but since there is no chance to get back to the original gate's time and place, you can't create a paradox and thus time travel is possible.

I tend to think that causality is a bit of a farce as well. Personally I feel that time isn't 1 dimensional but actually multidimensional. We move through time lineally but that is no different then a vector through a 3D space. If time is multidimensional then causality does not exist because if you were to kill yourself in the past, you are only killing one possible version of yourself (other versions still exist on tangent time paths in a multidimensional time).

nezumi.hebereke wrote:

But particle spin still doesn't strictly speaking break the rule of FTL, because particle spin can't be intentionally controlled - it always operates within the Uncertainty Principle. That's why we won't be able to transmit information via quantum entanglement.

Whether it can be intentionally controlled or not, you have an event that occurs in two places at once. Such a thing has very useful potential, such as finding out once and for all if time is truly relative or definite.

Arenamontanus wrote:

Actually not. If you check out the literature on time travel there is a lot of work based on wormholes, cosmic strings and Alcubierre drives that does not rely on the relativity of simultaneity. Note that this draws on general relativity theory, where there are spacetimes where various forms of simultaneity and absolute time *can* be defined (it is just that they rarely correspond to anything like what we normally use the term for: they are more like natural foliations of a manifold).

I was under the impression that the point behind the Alcubierre drive was that it didn't violate the local speed of light by forcing a bubble of spacetime to move around the ship, as opposed to trying to move the ship itself.

Arenamontanus wrote:

It is not the "without traversing spacetime" part that matters, it is that no-communication theorems show the entanglement cannot send information. Causality (and our current understanding of physics) are fine as long as you cannot send *information* from point A to B faster than light.

Even then, you'll have discrepancy issues involving spacetime. So long as the random spin of a particle exists at two points, and time is not a constant, then you can influence the past, however small that influence may be. Take your previous example of two people going at high speeds, two people being relatively stationary. Each fork has a two entangled particles, each linked to one of the other two participants. Fork 1 has a particle from each of pairs A and D Fork 2 has a particle from pairs A and B Fork 3 has a particle from pairs B and C Fork 4 has a particle from pairs C and D All forks record the observed particle motions in comparison to each other. One of them, according to special relativity, cannot synch up with the rest because the FTL nature of entanglement screws with that possibility. Therefore, at least one fork will be recording information from a few seconds into the past of another one of the forks. Why does this screw with causality? Because quantum mechanics as we know them today dictate that the very act of observing a particle alters the actions that the particle takes. Therefore, if one fork is observing the entangled motions of a particle from another fork's past, they are also influencing that particle's motions in the past. This is, of course, not a problem if time is a constant.

TBRMInsanity wrote:

I tend to think that causality is a bit of a farce as well. Personally I feel that time isn't 1 dimensional but actually multidimensional. We move through time lineally but that is no different then a vector through a 3D space. If time is multidimensional then causality does not exist because if you were to kill yourself in the past, you are only killing one possible version of yourself (other versions still exist on tangent time paths in a multidimensional time).

I've always felt that the more likely option is that time is a constant rather than relative concept, while the perception of the passage of time can be relative. This would completely eliminate all possibility of screwing with causality, while still explaining many issues in physics, like time dilation.