Angry_Ghost wrote:

There's a lot of commotion in the field of physics at the moment due to the fact that it appears, at present, that the speed of light has been broken.

Nah, it is business as usual. It is a commotion in the media, while experimental physicists expect it to turn out to be a measurement or equipment error.

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If this does in fact hold true, how if anything would you see it effecting our technological advancement in regards to Eclipse Phase? Would you see the setting stay pretty much the same or would fundamental aspects need to be altered in your opinion?

If it is just neutrinos that can move mildly FTL it doesn't change much, except to make the backwards in time problems already caused by QE comms even harder to escape. Remember, if you have a bit of FTL that is enough to transmit messages back into time to play the stock market, warn about xrisks or run transtemporal computations. If there was "instant" communications in the solar system there would be a unified mesh, much more vulnerable to takeover by malign software and much harder to separate for the different cultures. Egocasting would be even more powerful (and yes, it would now allow you to egocast back in time if there was enough bandwidth). If there was FTL ships, then the strategic situation becomes very nasty. You cannot protect yourself from FTL antimatter-tipped missiles: you cannot see them coming, and it is not hard to blow up habitats. Suddenly the military situation becomes one of MAD - but with dozens of players of varying levels of rationality, and various fractions who would love to see the major powers nuke each other.

My friend the neutrino physicist doesn't believe it is superluminal, and wrote that nobody in his team believes it (he is at the Super-Kamiokande project, where they send a similar a beam under Japan). But they are still excited, because if it *were* true... BTW, the original paper is here: http://arxiv.org/abs/1109.4897 (I love the page 10 illustration - they have to take into account the shift in location due to continental drift and earthquakes) As they conclude: "Despite the large significance of the measurement reported here and the stability of the analysis, the potentially great impact of the result motivates the continuation of our studies in order to investigate possible still unknown systematic effects that could explain the observed anomaly. We deliberately do not attempt any theoretical or phenomenological interpretation of the results."

puke wrote:

our best measured speed for neutrinos has ALWAYS been faster than light. but until now, those measurements have always been within the margin of error of the experiements, so we have assumed that they were bound by C.

What would that speed measurement be? Supernova SN 1987A? (there the early arrival is likely just due to the photonic shockwave getting delayed on its way to the surface) The existence of superluminal particles doesn't necessarily invalidate relativity. It might invalidate causality instead.

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I mean, its not like a "laser engine" is going to be moving your ship at the speed of light now, is it?

Actually, lightsails and laser-pushed lightsails are very effective engines. And an antimatter-powered gamma-photon rocket is the theoretically optimal rocket. It doesn't make you move at lightspeed, but it has the best specific impulse possible.

I hate things that threaten to invalidate causality, because... Wait... Dammit? :) Anyhow, as to other EP effects: On the gatecrashing end you've got the mothership/colony ship support. You're no longer limited to what you can send 'down the hole'. The Solar System (and extrasolar colonies) just got a lot 'closer' together. Consider what transit and communication time between Europe and East coast of North America resulted in during the course of the late 17th and 18th centuries. Even today, transit lag has significant effects on global projection of power. We can deliver a military force of light infantry anywhere in the world in a hurry, but for any sort of ongoing operation you need a tremendous airlift and sealift capacity for heavy equipment...And that includes bombs. Munitions are one of those cargos which are extremely dense for their utility. Particularly given U.S. air superiority > air-ground strike strategies it takes a great deal of time and transport to stage munitions for a major offensive. Given light-speed transport, many of the factions which currently exist in EP would not enjoy the distance and isolation which they do now. In some cases that might result in weaker factions which are purely reliant upon isolation for protection ceasing to exist in a sudden and spectacular fashion. FTL bombardment has already been mentioned. Overall, I think the possibility for a major militarized state to exert (or attempt to exert) extensive system-wide control becomes far more likely, and then you're playing a rather different game in terms of its social and political paradigms.

The speed reported is only very fractionally above the speed of light--they arrived only 60 nanoseconds early after a trip of 730 kilometers. FTL communications is a cool idea, but if the FTL grid functions at a speed of less than 1.00002c it's difficult to see how the possession of the technology would offer that much of an edge. This is especially the case if you exclude time travel effects from consideration, as Eclipse Phase FTL seems to do.

Smokeskin wrote:

Arenamontanus wrote:

If it is just neutrinos that can move mildly FTL it doesn't change much, except to make the backwards in time problems already caused by QE comms even harder to escape. Remember, if you have a bit of FTL that is enough to transmit messages back into time to play the stock market, warn about xrisks or run transtemporal computations.

That's not necessarily true. We don't really know how FTL "works". Some thought experiments along the line of "what if FTL signals stayed on the light cone" obviously allows you to send messages back in time. Honestly that seems to be a rather crazy assumption that can only come about from people who see some sort of philosophical meaning behind special relativity and then confabulate freely from there.

FTL is by *definition* signals that go outside the light-cone. A signal that stays on it is a lightspeed signal.

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But if FTL signals don't travel along the light cone, you just get messages arriving faster than photons, which is a big deal if you want to dodge lasers or your fellow stock traders only get outer system news by radio, but otherwise isn't that interesting.

I have no desire to bring up the argument again (I think I have done it at least four times on this forum; search past posts or google the topic), but any FTL messaging either means you have to throw all of relativity theory out of the window (a mathematically sensible, empirically well tested theory) or you have to accept messages from the future. You cannot have FTL, relativity and causality at the same time - choose two.

And if you could explain it to me like I was a five year old, that would be great :D I really should try and educate myself on things like general relativity, but every source I can find assumes a greater understanding of physics than I currently have. Does anyone have any resources that would guide me from a high school level of physics up to a basic understanding of such things?

Smokeskin wrote:

No, lightspeed signals don't allow you to communicate instantly with anything you see on your past light-cone, which is basically what happens in the instant-comms-break-causality-breaking examples. If you stick to relativity's idea of what simultaneous is, it makes a sort of sense to think that way - except that that idea comes from the speed of light, and if you can exchange information faster than that, then the idea suddenly makes no sense.

Worked example: I am sitting at the origin at time 0. I send a FTL message to the event at distance 1, time 0.5 (it could be one light-year away, half a year into my future; lets set light-speed to 1 in this example). This signal is not on my light cone but outside of it. These hyper-speed messages are not instantaneous according to their senders, they just travel at twice light-speed. Now, an observer moving with a speed of 94% light-speed (which makes gamma 3) happens to be there to receive it. In his coordinate system, which we assume is synchronized with mine so that we both agree on the origin, the coordinate is 1.58 and the time is -1.32 - he will get the message before I sent it, at least according to his clock. He can't quite manage to send a normal light-speed message back to the origin in time to tell me about what I am going to transmit (he is too far away), but if he has a hyper-speed transmitter he can definitely do it that way. He sends it one length unit back and half a time unit forward just like I did but in the reverse direction - it will arrive at (0.58, -0.828) in his frame, or at (-0.60, -0.84) in my frame. Plenty of time for the message to get to the origin via sub-light signals from there, and tell me what I will be sending - or prevent me from doing it. This might not make much intuitive sense, but this is what happens when you do the math (just try the Lorentz transformations and draw a picture on gridded paper). If you allow signals to get in and out of your lightcone, then there will be observers who can bounce them back in such a way that you get backwards in time messages.

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Arenamontanus wrote:

any FTL messaging either means you have to throw all of relativity theory out of the window (a mathematically sensible, empirically well tested theory)

Newtonian mechanics is mathematically sensible and empirically well tested theory too, it just doesn't apply outside of its boundaries. Finding that relativity theory needed adjustments to describe FTL events wouldn't be that great of a surprise, or mean that we had to throw it all out, at all.

You misunderstand what I was saying. Relativity has no problems at all with FTL as the above example shows. It is just that FTL+relativity = future events can affect past ones = causality as we know it has to go. The other option is: FTL + causality = you have to remove relativity. And it is not going to be a simple theory or just a minor adjustment, since you need to throw out the invariance requirements the theory is built on. You would need an entirely different symmetry group behind it, yet you need to patch it together with relativity for all sub-light speeds.

(Sorry for jumping from communications back to actual physical travel) I don't pretend to know all but i have come across the concept put forth by Miguel Alcubierre wherein one would increase gravity before an object and reduce it behind while creating a bubble of flat space in the middle to travel at FTL speeds without actually breaking relativity? http://en.wikipedia.org/wiki/Alcubierre_drive http://www.daviddarling.info/encyclopedia/A/Alcubdrive.html Thoughts? Comments? *honestly curious*

Alright science guys, riddle me this: If I'm in the Future, and I want to send an FTL message to me in the past, how do I [i]aim the signal[/i] into the past.

Arenamontanus wrote:

Smokeskin wrote:

Ok, so the signal arrives at distance 1, time 0.5. We have our observer A moving at 94% c. We also have an observer B there at the same spot, sitting still relative to the sender. Obviously, both A and B receive the signal at the same time relative to the sender. They both send it back a 2c signal, which both arrive at the original sender simultaneously.

No. Remember relativistic velocity addition. Or even plain Galilean velocity addition. Sending a message at a certain speed *relatively to you* doesn't mean another observer will agree on the speed. You are assuming A and B will agree on the speed of each other's signals, but they will only do that if they are either immobile relative to each other or sending lightspeed signals.

You're missing the point. Whether or not FTL signals would, unlike light, be affected by velocity addition, isn't relevant. The real issue lies before the signal return. No matter what speed and clock time the observers agree on, the FTL signal going from the sender is transmitted so it will arrive at the stationary receiver when the moving receiver is at the same position - this is obviously a certain point in spacetime even if observers have clocks running at different speeds. Now, what you're saying is that the moving receiver, being at the same point in spacetime as the stationary receiver, doesn't see any signal even though the stationary receiver sees it! Do you really believe that the Lorentz transformations are telling you that FTL signals don't travel along defined spacetime paths? Does relativity theory really predict that FTL signals take an infinite number of spacetime paths, and at which path you can pick up the signal is defined by the speed of the receiver (what mechanism, what property of elementary particles should be responsible for this, and how relativity theory could predict this peculiar and novel interaction from math alone is mindboggling)? Or maybe an FTL signal's path through spacetime isn't described by what an observer thinks the sender's clock is at? To reiterate the issue: A sender transmits an FTL signal to a receiver stationary relative to the sender. At the same point in spacetime as the signal is received, another receiver is present and moving at 94% of c. - Does the moving receiver pick up the signal at that point? - If yes, is this signal received in the sender's past for both receivers, one of them, or none of them? - If not, at what point would the moving receiver pick up the signal, and what would a stationary receiver at that point in spacetime see?

Smokeskin wrote:

Do you really believe that the Lorentz transformations are telling you that FTL signals don't travel along defined spacetime paths?

Please tell me what spacetime paths QE communications are supposed to follow. Actually, even non-informative quantum correlations seem to have undefined spacetime paths. This is not the fault of SR and the Lorentz transformations, it is the fault of reality for allowing quantum weirdness.

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To reiterate the issue: A sender transmits an FTL signal to a receiver stationary relative to the sender. At the same point in spacetime as the signal is received, another receiver is present and moving at 94% of c. - Does the moving receiver pick up the signal at that point? - If yes, is this signal received in the sender's past for both receivers, one of them, or none of them? - If not, at what point would the moving receiver pick up the signal, and what would a stationary receiver at that point in spacetime see?

Yes, a signal picked up at a spacetime event can be picked up by any observer at that event (you can imagine the stationary observer sending a light impulse to the moving observer, and then allowing the interval between them go to zero). The sender will not see the reception of the signal in his past *or* future at the time of sending, since it is outside of his lightcone (eventually he will of course see it as the light from that reception even reaches him normally). Strict causal ordering of events and signals only work if they all stay sublight.

This is one of those few topics in Eclipse Phase that I actually ponder invoking the MST3k Mantra. Usually I enjoy watching people nitpick at the science behind things, but this topic is getting really old.

Perhaps your future self never made it to a point in time where viable 'messages from the future' are possible? Something to ponder and worry about.

Arenamontanus wrote:

Axel the Chimeric wrote:

I feel sorry for you, Anders, every time this topic comes up.

It is partially self inflicted. I should have learned not to touch it. (darn, why do I never get PMs from my future self not to get into certain threads!?)

Anders! This is future you, from the future. You need to PM me all your bank details immediately. I - and thus you - have forgotten them! Remember, I am future me, so you can trust me.

UnitOmega wrote:

Arenamontanus wrote:

*Maths*

That's nice, and all Anders, and I'm sure all your calculations are right, it's just I have no idea what you said. Could you tell it to me again, only in Star Trek-esque Simile, Metaphor and Allusion?

Ok, I'm doomed to try :-) Here is the non-FTL situation: Imagine yourself, at this very moment. You turn on and turn off a lamp, and the light goes off in all directions. This expanding spherical shell of light marks the edge of your future light cone. Future because it is, well, moving towards the future. Cone because it is really like a four-dimensional cone with the apex at the moment you lit the lamp and built up from spherical slices, just like a normal 3D cone would be built up from circles. Anything you do this moment can only affect events inside the future light cone, since signals about it can only reach its interior (or edge, if it is light) - they will not have the speed to get past the light shell. One can also imagine a past light cone, which would have been a spherical shell of light coming in from infinity, finally hitting your lamp just at the moment you lit it. Hard to arrange in practice, but it is merely a way of marking the points in space and time that could have sent you a light signal you would have received at the "now" moment. When you look around, all you see is things inside your past light cone. Their light is just now reaching your eyes - some of it was sent long ago from the stars on the sky, others was sent nanoseconds ago from your computer screen. You cannot see events that are outside the past light cone since their light has not reached you. And of course, you cannot hear or smell anything from the outside since the even slower sound or odor motion has not even gotten that far. In relativity we can only speak of "past", "future" and "right now" in relation to where we are and our light cones. Everything in your past light cone is your past, everything in your future light cone is your future and that point of intersection is "here and now". We all got our own light cones, and of course they overlap. When I write this post, my future lightcone includes the event of you reading it - you have my current "here and now" in your past. We both agree on this. People onboard fast spaceships will see things in a way we stay-at-homes will claim is distorted, and vice versa. Just like rotation mixes left-right and front-back, so does moving fast mix time and space like a weird kind of rotation. Hence the classic effects of time dilation, length contraction and so on. We will not agree on distance or timing measurements. This is very confusing. But an important thing relativity says is that we all agree on how light is moving - we all see those light shells move at the same speed, the speed of light. This is *the* cornerstone of relativity theory, and you can actually derive the whole thing from this assumption. In regards to the light cones this means that everybody will agree on what is past and future since we can compare our light cones - we disagree on lengths and timing, but we all agree on when and where light cones meet, and hence what came before what. OK, what happens if we throw FTL into the mix? Now we can send messages to places and times outside our light cones: they get there before the light does. Does the message arrive before or after I sent it? *There is no answer*! Before and after depends on who is looking. Some observers will see me send the message and then its arrival. Others will see its arrival and then me sending it. It all depends on where they are and how they are moving. It really isn't any stranger than people disagreeing on whether something is to the left or right. But now we are disagreeing on the order of things. Normally this chaos doesn't happen because all slower than light signals and spaceships keep inside the lightcones, remaining inside the domain where past and future are well defined for everybody. Worse, if you send something outside the lightcone and then back, then you can (as in my examples) end up with it arriving before you sent it - the weirdness can get into our normal world of cause and effect too. Guess why so many people think FTL must be impossible? So, yes, you could set up a futurephone that allows you to call yourself in the future if you had FTL comms. You will say some things to your future self, get some responses and a while later the phone rings and you will have the same conversation again. Can you give different answers? According to most physicists who have thought about it, no. You will already have had the conversation. Most likely the universe simply maintains consistency: contradictory and paradoxical events never happens (that doesn't preclude various trickery, as evidenced in Greg Egan's "The hundred lightyear diary"). Bad news for free will if you believe in the wrong sort :-) http://www.concatenation.org/futures/whatsexpected.pdf Not sure if this helps in any way. This is a profound area of physics and philosophy we are dealing with, the causal structure of spacetime. I just wished it was easier to run in rpgs!

Arenamontanus wrote:

Smokeskin wrote:

To reiterate the issue: A sender transmits an FTL signal to a receiver stationary relative to the sender. At the same point in spacetime as the signal is received, another receiver is present and moving at 94% of c. - Does the moving receiver pick up the signal at that point? - If yes, is this signal received in the sender's past for both receivers, one of them, or none of them? - If not, at what point would the moving receiver pick up the signal, and what would a stationary receiver at that point in spacetime see?

Yes, a signal picked up at a spacetime event can be picked up by any observer at that event (you can imagine the stationary observer sending a light impulse to the moving observer, and then allowing the interval between them go to zero). The sender will not see the reception of the signal in his past *or* future at the time of sending, since it is outside of his lightcone (eventually he will of course see it as the light from that reception even reaches him normally).

I fully agree. Hold that thought and tell me: at this event at a defined point in spacetime, is the signal received in the sender's past for both receivers, one of them, or none of them? I know you're saying "one of them", but that would mean that the same point in spacetime was both in the sender's past and not, simultaneously! Does this not strike you as odd?

Arenamontanus wrote:

Smokeskin wrote:

I know you're saying "one of them", but that would mean that the same point in spacetime was both in the sender's past and not, simultaneously! Does this not strike you as odd?

No :-) Honestly, I don't know whether I understand relativity or have just become totally used to its stranger properties. I am saying that both two receivers moving relative to each other at the same point will be able to receive the FTL message simultaneously (simultaneity is defined since they are inside each other's light-cones, specifically at the apex of both of them). But when this event happens relative to what the sender thinks is past or future, that is ill-defined. The "static" receiver will have a clock showing it happens a bit into the future of the sender, the moving receiver will have a clock showing it happened in the past of the sender. None of them are wrong, since simultaneity is not defined outside light-cones.

Then look at it from the sender's POV. His signal is received by the two receivers at a certain point in spacetime which he has a clear and singular idea of how it relates to his past, present and future. Or assume that both receivers send back a light signal - these originate from the same point in spacetime and thus both arrive at the original sender at the same time. This contradicts your original calculation where you stated:

Arenamontanus wrote:

he will get the message before I sent it, at least according to his clock. He can't quite manage to send a normal light-speed message back to the origin in time to tell me about what I am going to transmit

He can't quite make it, but better than if he had been a stationary receiver, right? Because the signal was sent back in time. Except that seems to directly contradict our understanding that both receive the signal at the same point in spacetime. It seems to me that the Lorentz transformations are misused here. They concern how _observers_ order events and measure time and length, but not what _actually_ happens or how things are. If you can explain to me how a signal can be sent to a single point in spacetime yet be received at different times, this mystery would be cleared up. Relativity is perhaps a bit strange, but it isn't so strange that an observer thinks a point in spacetime can be at different times, is it?

Angry_Ghost - don't stress about it. It's a freaky topic that 90% of people don't get (myself included) no matter what you say to them, so it will keep coming up again and again, forever, and each time we'll all watch, scratch our heads and write it off as witchcraft, until the NEXT awesome idea comes up again and we still haven't quite figured it all out. I still read each of these threads because every time I (think I) learn something new, or understand the topic a little better. And I make the same mistake as Arenamontarous by trying to repeat it on other forums.

nezumi.hebereke wrote:

Angry_Ghost - don't stress about it. It's a freaky topic that 90% of people don't get (myself included) no matter what you say to them, so it will keep coming up again and again, forever, and each time we'll all watch, scratch our heads and write it off as witchcraft, until the NEXT awesome idea comes up again and we still haven't quite figured it all out. I still read each of these threads because every time I (think I) learn something new, or understand the topic a little better. And I make the same mistake as Arenamontarous by trying to repeat it on other forums.

Well, in this case what is repeated is something that leads to gross inconsistencies, meaning it is probably wrong. If you end up thinking the same event is both at one and two points in spacetime, you probably did something wrong.

Azathoth wrote:

http://aether.lbl.gov/www/classes/p139/exp/experiment8.html

That is not the situation that occurs here. Two different observers ordering events differently is ok - but when ONE observer thinks that the SAME event happens BOTH at one specific time AND at two different times, you messed up.

The_Ren wrote:

(Sorry for jumping from communications back to actual physical travel) I don't pretend to know all but i have come across the concept put forth by Miguel Alcubierre wherein one would increase gravity before an object and reduce it behind while creating a bubble of flat space in the middle to travel at FTL speeds without actually breaking relativity? http://en.wikipedia.org/wiki/Alcubierre_drive http://www.daviddarling.info/encyclopedia/A/Alcubdrive.html Thoughts? Comments? *honestly curious*

Well, according to my understanding the Alcubierre drive would work, but it is impractical. Its energy requirements are rediculously huge. Suppose we were to be able to do a perfect matter to energy transformation and capture 100% of the energy produced (This violates several of the laws of physics right there.) If we were to convert the estimated mass of the known Universe in to energy, we would still be short. By several orders of magnitude. Hence the "impractical". At that level of energy...well, let's just say, weird things will start to occur.

Azathoth wrote:

So then I asked how quantum entanglement (a confirmed phenomenon, responsible for QE comm in EP) managed not to violate causality, and he explained that if you think about it closely no information is actually transfered. I'll have to ponder over what he said some more, but I wanted to share. :)

So, QE comms are only useful for shipping egos and newscasting? Hard scientific data still has to go by slowboat. :)

Azathoth wrote:

So then I asked how quantum entanglement (a confirmed phenomenon, responsible for QE comm in EP) managed not to violate causality, and he explained that if you think about it closely no information is actually transfered. I'll have to ponder over what he said some more, but I wanted to share. :)

Quantum entanglement as we know it is not sufficient for EP-style QE comms. We have no control over the state of entangled particles. We can only perform a measurement on one of the particles, and the other particle will be affected by the measurement. Even if this is FTL, it only allows us to to end up with two correlated random strings, rather than transmit any information.