JJ-Trek/ IDW Continuity and Discontinuities

[Idran]

My brain hurts.

"Before" to me would be the unaltered timeline, with "after" being the edited one. Does that answer the question?

Not really? You're still pushing it onto a specific example there, but I'm asking for your definition of "before". That is, if someone hypothetically compiled a dictionary of "every word as WebLurker means it when they use it", I'm asking what would be written under the word "before".

I mean, no offense intended at all, WebLurker, but if you can't say what specifically your definition of the word "before" is as you use it, and if the fundamental source of the confusion/disagreement is, as it seems, that you mean something different by the word "before" than Christopher does, then how will this discussion ever end? You won't be able to identify that disagreement and come to a resolution without being able to define the word that's the cornerstone of the disagreement itself. Right now you're caught in a loop of "I am saying that the previous timeline happened before"/"But that makes no sense because of this"/"But why doesn't it make sense, before the timeline was this and after it was this"/etc... And it'll just keep going around in circles forever until one of you drops the discussion so long as that fundamental issue isn't resolved.

 

[Avro Arrow]

I mean, no offense intended at all, WebLurker, but if you can't say what specifically your definition of the word "before" is as you use it, and if the fundamental source of the confusion/disagreement is, as it seems, that you mean something different by the word "before" than Christopher does, then how will this discussion ever end?

Only one possible way: Data has to decompress the main shuttlebay.

 

[WebLurker]

Because that is a self-contradictory statement. It's meaningless. One version of a single moment in time cannot change into a different one, because change requires the passage of time. It requires a "before" version and an "after" version, and as I've been trying to explain to you, a single moment in time cannot come after itself. All the words you're using -- "overwriting," "replaced," "no longer exists" -- assume that time has passed. They're referring to two consecutive versions, to versions that occupy different moments of time. But we are talking about two different versions of the same moment in time. So none of those words that require duration or consecutivity are applicable here.

I don't know why it's so hard for you to understand this. If two things happen at the same moment, they are simultaneous, not consecutive. That is a very simple, basic concept. That is the literal definition of those words.

I guess the way I was looking at it was, if you traveled to timeframe X in the past to change something, you would've prevented the original outcome from happening, so there'd be no reason to have the timeline doubled; the original event never even happened, since your version is the way things went (which is what I meant by "overwrite"). I'm probably doing a bad job of explaining myself and if it's bad science, it's bad science. But, even if wrong, does it make sense why I'm having a little trouble processing why "change requires the passage of time." when you're rewinding the clock (so that the only extra time is added to your personal timeline, not the overall timeline)?

It's ignoring the way time travel is usually portrayed in fiction, but -- news flash -- fiction isn't real. It deliberately portrays time travel in a physically absurd and logically contradictory way because that is more dramatically satisfying. But you should never, ever mistake what you've been told by fiction for a legitimate grounding in how science works. Fiction routinely portrays reality unrealistically. For instance, anyone who's ever witnessed a thunderstorm knows that the sound of the thunder comes after the lightning unless it's right on top of you, but for some bizarre reason, movie sound designers always, always make the thunder simultaneous with the lightning even though virtually everyone in the world has firsthand experience telling them that's wrong. And then there are all the sci-fi movies where you can see the stars outside a spaceship window even when it's brightly lit inside, when everyone who's ever looked out a window at night when the lights are on should know that's wrong. Fiction takes license. It's not a guide for how things really work.

Very true.

No, because these things are relative. How you perceive the universe depends on your point of view. You're still trying to assume there's a single absolute interpretation of things, but Einstein blew that notion out of the water over a century ago.

I see.

Free will exists, because the decisions you make haven't been made yet. But you only get to make them once. If you go back in time, it might look like events are happening a second time, but they aren't. You're just seeing their one and only occurrence a second time. It's like replaying a ball game on your DVR. You see the game played again, but nothing you do can change the outcome. Which can make you feel like you have no free will. But that's just because the choices were already made. Free will isn't the illusion; the absence of free will is an illusion created by time travel.

Put another way, our free will is always constrained by our circumstances. We're free to do what our situation allows us to do, and some situations are more constraining than others. The analogy I like to use is that if you're standing on an open plain, you have free will to move anywhere you want in two dimension (though not in the third), but if you then fall off a cliff, your freedom to decide your direction of movement becomes far more restricted. Time travel is like falling off a cliff. It puts far more limits on your freedom to affect outcomes than you would normally have, because it's an atypical situation.

I like that explanation (I got the original question from that time travel source book for the late, lamented Star Trek RPG that LUG did, which outright suggested that predestination paradoxes would eliminate free will. At the time, that didn't make sense to me, since from the perspective of the time travelers, their trip into the past is part of the future of their personal timeline, so they're making decisions about their futures in the past. Like how you explained it, though.)

Of course, again, fiction routinely portrays it unrealistically for dramatic effect, since it's less interesting if your characters have no power to affect events (although there have been a number of powerful time-travel stories built around the immutability of history, like the movie 12 Monkeys or Heinlein's "--All You Zombies--").

Well, I don't know. If there was only one time travel model used in fiction, sci-fi stories would get really dull.

But you're still seeing those events from the perspective of the characters while they're making the choices. If you want to talk about the dynamics of time travel in broader terms, you have to step outside that subjective POV and look at the shape of the timestream more objectively, which is akin to looking back on it after all the choices have already been made

Okay, I guess (my brain's starting to hurt again).

Again, the key is to understand that definitions are relative to your point of view. The timeline is the "original" from Archer's and Daniels's point of view, but that's relative to their own subjective experience of time. It's not a cosmic absolute. From the perspective of a different observer with a broader view of the multiverse -- which is the perspective we need to adopt if we want to analyze the dynamics of the time travel -- all those alternate paths are simply part of the graph, and characters see them as "original" or not based on their own subjective journeys and which ones they perceive first.

Okay. (I'd suggest that Daniels would presumably have equipment to track time travel and its effects and would know how things worked, but okay.)

Of course. I was talking about self-consistent time loops in general.

Got it.

That is the exact point I already made -- that the writers using that term assumed that the inversion of conventional cause and effect was a paradox, but they were wrong to think that, because the scientific reality of it is that it's the opposite of a paradox. It's important to let go of our everyday preconceptions of causality, time, and space when we're talking about things like time travel, because those are situations that lie outside our everyday experience and thus our conventional intuitions don't apply. Which is why we have science and math to let us calculate what would actually happen in situations where our assumptions and expectations fall apart.

Or we could use the old standby fudge that our best science of today will be disproven tomorrow by new advances (if we're trying to compare real life theories to fictional stories).

I don't understand the question.

I was just curious, if someone hired you to write a time travel story that did not use the model you've been describing on this thread, which kind of alternative would you pick?

Why do people always assume that every time travel has to happen in the exact same way? That is not how physics works. There are countless examples of the same physical laws producing very different outcomes when the initial conditions are different. The same cosmological processes that produce stars also produce planets and asteroids and comets. The same geological processes that create continents also create ocean basins. The same genetic and environmental mechanisms that led to the evolution of mammals also led to the evolution of birds. So why can't the same laws of time travel produce self-consistent loops in some conditions and branching timelines in others? I don't for the life of me understand why people jump to such a bizarre conclusion.

Sure, I'll agree that there can be exceptions to time travel rules under the right circumstances. I guess then, the only question is if the circumstances are special enough to make the exceptions. (For example, I question the "time travel created a parallel universe" model for the Abramsverse Trek movies not because I don't think there could be an exception to make that happen, I just don't think the evidence from the movie supports that conclusion. However, that's gets into subjectivity and I don't want to restart the debate there, so let's just leave it at that, please.)

Indeed, according to one interpretation, quantum physics pretty much requires both to happen in any time travel. Quantum physics is probabilistic, after all. So quantifying a particle's path through time requires summing all its possible paths. In short, if there's a chance that it will cause its own past and a chance that it will alter its own past, then both outcomes will happen. To put this in human terms, let's say you go back in time to kill Hitler or whatever and you have a 50/50 chance of pulling it off. So this will result in a timeline where you fail to kill Hitler and everything stays the same, and a timeline where you kill Hitler and everything is different. It's not a choice between a loop and a parallel; both of them are required to happen.

Cool.

Scientifically, this is gibberish. It wouldn't happen that way. As I've already told you before (I'm getting sick of repeating myself), what I've done in my DTI novels is to rationalize this absurd fictional conceit by positing that the parallel timelines reconverge once time catches up with the moment of the original time travel. I've discussed the physics of this in Watching the Clock and my online notes to same, so I refer you to those.

Sure, thanks, I like those annotations you write.

I will admit that, subjectively, I'm not a big fan of the parallel timelines theory, since I think that the more interesting stories come from other models (and given that I seriously doubt that time travel will ever become a reality, I guess I don't see the harm in being unrealistic). So, I do have that bias, I guess.

Not really? You're still pushing it onto a specific example there, but I'm asking for your definition of "before". That is, if someone hypothetically compiled a dictionary of "every word as WebLurker means it when they use it", I'm asking what would be written under the word "before".

I mean, no offense intended at all, WebLurker, but if you can't say what specifically your definition of the word "before" is as you use it, and if the fundamental source of the confusion/disagreement is, as it seems, that you mean something different by the word "before" than Christopher does, then how will this discussion ever end? You won't be able to identify that disagreement and come to a resolution without being able to define the word that's the cornerstone of the disagreement itself. Right now you're caught in a loop of "I am saying that the previous timeline happened before"/"But that makes no sense because of this"/"But why doesn't it make sense, before the timeline was this and after it was this"/etc... And it'll just keep going around in circles forever until one of you drops the discussion so long as that fundamental issue isn't resolved.

No offense taken.

Well, now my brain is really hurting. How do you define "before" and "after" beyond looking it up in a Webster's? The same way you describe a color, I guess?

Sorry, but I'm not sure I can really answer the question and have at this point tried to shift from arguing against Mr. Bennett to trying to understand his position, with varying degrees of success.

 

[Christopher]

I guess the way I was looking at it was, if you traveled to timeframe X in the past to change something, you would've prevented the original outcome from happening, so there'd be no reason to have the timeline doubled; the original event never even happened, since your version is the way things went (which is what I meant by "overwrite"). I'm probably doing a bad job of explaining myself and if it's bad science, it's bad science.

The fundamental mistake that you keep making is confusing the observer's subjective viewpoint with the only viewpoint. We've known for over a century for now that relativity is fundamental to the universe: There is no single absolute frame of reference that works for everyone, and the same physical interaction can appear different when measured by observers in different frames of reference. If you're standing on the ground watching a train go by, it looks like the train is moving east; but if you're on the train watching the ground outside, it looks like the ground is moving west. And as long as the train is moving at a constant rate, the physics that affect an object on the train will be consistent with a reality where the train is standing still and the ground is moving.

By the same token, if one observer is moving normally through the timestream and another observer is moving backward in time, they're going to measure cause and effect and change differently because of their different perspectives. You persist in assuming the time traveler's frame of reference is the only one that exists, and that is the mistake that's preventing you from understanding the rest of this conversation.

But, even if wrong, does it make sense why I'm having a little trouble processing why "change requires the passage of time." when you're rewinding the clock (so that the only extra time is added to your personal timeline, not the overall timeline)?

When something changes, there is a version before the change and a version after the change. One comes after the other, therefore time passes between them. That's what time is -- a process of change. If things didn't change, we'd have no way of measuring time. So change is what defines time itself. Time and change are inseparable concepts.

Put another way, change is something that happens within time. Time is just a collective word for all the changes that happen in the universe. So it's contradictory to speak of the shape of time itself going through a change. Then there'd have to be a higher dimension of time that time existed within, so that time itself could move through higher-time (Hypertime?) and thereby change. It's a paradoxical idea. Granted, there are some fringe theories about a second dimension of time, and I did invoke these in Watching the Clock, but it's stretching credibility to the limit.

Well, I don't know. If there was only one time travel model used in fiction, sci-fi stories would get really dull.

Sure, which is why I understand the dramatic necessity of the nonsensical "overwriting" conceit. I'm just pointing out that it's unrealistic and that you shouldn't expect time travel to actually work that way.

Okay. (I'd suggest that Daniels would presumably have equipment to track time travel and its effects and would know how things worked, but okay.)

Even temporal agencies are observing the universe from within, and that makes their perceptions subjective and incomplete. Again, the fundamental thing to understand in modern physics is that no one observer has all the answers -- only a partial, subjective view of reality dependent on their frame of reference. So you need to consider multiple different perspectives and how they relate to each other in order to get a grasp on the larger truths. (Much as in other aspects of life -- you need to consider other points of view and recognize the limitations and biases in your own in order to gain wisdom.) Relativity shows that observers moving differently will measure space, time, and motion differently, and they will all be equally right within their own frames. Quantum physics shows that a given particle or interaction can happen multiple different ways at the same time, but we can only measure one at a time, because how we measure something inevitably affects how we observe it.

Well, now my brain is really hurting. How do you define "before" and "after" beyond looking it up in a Webster's? The same way you describe a color, I guess?

You do it by understanding that there is no one absolute definition -- that it depends on the observer's movement through time. It's the same as movement through space. How do you define "forward" and "backward"? If you're moving east, then east is forward. If you're moving west, then east is backward. The definition is relative to your frame of reference. "Before" and "after" are directions in time and causality. They describe the order in which events are perceived by an observer. And if two observers are moving in different directions in time, they will perceive that order of events differently.

 

[Idran]

First off; in hindsight yeah I see that you've shifted goals, WebLurker, and my apologies for not recognizing that. Second:

"Before" and "after" are directions in time and causality. They describe the order in which events are perceived by an observer. And if two observers are moving in different directions in time, they will perceive that order of events differently.

Oh man, now that you've said this in precisely this way, Christopher, I am really tempted to start rambling about the problem of simultaneity, because it's such an amazing result that really frames how fundamental relativity is to the universe. It's maybe one of my favorite unexpected consequences in physics. But I'm worried it would just confuse things even further so I'll wait a spell.

I'll just say, WebLurker, that there's something underlying here that is perfect at highlighting just how our intuition of spacetime based on our own personal experiences and day-to-day life turns out to be flawed, and I'll go into detail down the line once the confusion seems settled.

 

[WebLurker]

The fundamental mistake that you keep making is confusing the observer's subjective viewpoint with the only viewpoint. We've known for over a century for now that relativity is fundamental to the universe: There is no single absolute frame of reference that works for everyone, and the same physical interaction can appear different when measured by observers in different frames of reference. If you're standing on the ground watching a train go by, it looks like the train is moving east; but if you're on the train watching the ground outside, it looks like the ground is moving west. And as long as the train is moving at a constant rate, the physics that affect an object on the train will be consistent with a reality where the train is standing still and the ground is moving.

So, the perception of the order of events, cause and effect, etc. in time travel is as illusory as how it looks like the train is moving? The train is going the same direction regardless, but, it looks different depending on our position and all that?

By the same token, if one observer is moving normally through the timestream and another observer is moving backward in time, they're going to measure cause and effect and change differently because of their different perspectives. You persist in assuming the time traveler's frame of reference is the only one that exists, and that is the mistake that's preventing you from understanding the rest of this conversation.

So, would a fair analogy be comparing watching a Star Trek show with a chronology of the franchise. If I'm watching the show, I can fast forward and rewind within the specific episode, but can't see what happens beyond the scope of it, whereas, if I'm looking at the chronology, I can see every thing that happened in the franchise before and after. (To put it another way, would your "objective" viewpoint being like seeing the entire chronology of the Universe from beginning to end laid out on one big graph?)

Another question, can this big picture assumption be viewed in its entirety from any point? Say, for example that a Trek character, say Rain Robinson from 1997 was shown the big picture from her home time. Would she be able to see everything, or would stuff that happened in her future not be visible to her?

When something changes, there is a version before the change and a version after the change. One comes after the other, therefore time passes between them. That's what time is -- a process of change. If things didn't change, we'd have no way of measuring time. So change is what defines time itself. Time and change are inseparable concepts.

So, you can't rewind and skip the time that the "process of change" by jumping from say your present, to spending five weeks in the past, and then returning to the exact moment you left in the present again?

Put another way, change is something that happens within time. Time is just a collective word for all the changes that happen in the universe. So it's contradictory to speak of the shape of time itself going through a change. Then there'd have to be a higher dimension of time that time existed within, so that time itself could move through higher-time (Hypertime?) and thereby change. It's a paradoxical idea. Granted, there are some fringe theories about a second dimension of time, and I did invoke these in Watching the Clock, but it's stretching credibility to the limit.

Okay?

Sure, which is why I understand the dramatic necessity of the nonsensical "overwriting" conceit. I'm just pointing out that it's unrealistic and that you shouldn't expect time travel to actually work that way.

So, this conversation is mainly about how time travel would theoretically work in the real world, not about it in fictional worlds? Okay, sorry for not quite getting that earlier.

Even temporal agencies are observing the universe from within, and that makes their perceptions subjective and incomplete. Again, the fundamental thing to understand in modern physics is that no one observer has all the answers -- only a partial, subjective view of reality dependent on their frame of reference. So you need to consider multiple different perspectives and how they relate to each other in order to get a grasp on the larger truths. (Much as in other aspects of life -- you need to consider other points of view and recognize the limitations and biases in your own in order to gain wisdom.) Relativity shows that observers moving differently will measure space, time, and motion differently, and they will all be equally right within their own frames. Quantum physics shows that a given particle or interaction can happen multiple different ways at the same time, but we can only measure one at a time, because how we measure something inevitably affects how we observe it.

Fair enough.

You do it by understanding that there is no one absolute definition -- that it depends on the observer's movement through time. It's the same as movement through space. How do you define "forward" and "backward"? If you're moving east, then east is forward. If you're moving west, then east is backward. The definition is relative to your frame of reference. "Before" and "after" are directions in time and causality. They describe the order in which events are perceived by an observer. And if two observers are moving in different directions in time, they will perceive that order of events differently.

But the reality of the events don't change, anymore than the directions of East and West not changing, regardless of which is behind you. Or is that not important to this model?

First off; in hindsight yeah I see that you've shifted goals, WebLurker, and my apologies for not recognizing that. Second:



Oh man, now that you've said this in precisely this way, Christopher, I am really tempted to start rambling about the problem of simultaneity, because it's such an amazing result that really frames how fundamental relativity is to the universe. It's maybe one of my favorite unexpected consequences in physics. But I'm worried it would just confuse things even further so I'll wait a spell.

I'll just say, WebLurker, that there's something underlying here that is perfect at highlighting just how our intuition of spacetime based on our own personal experiences and day-to-day life turns out to be flawed, and I'll go into detail down the line once the confusion seems settled.

I'll look forward to your observations.

 

[Christopher]

So, the perception of the order of events, cause and effect, etc. in time travel is as illusory as how it looks like the train is moving? The train is going the same direction regardless, but, it looks different depending on our position and all that?

Not "illusory," because that implies it's unreal and that there's a superior, "true" perception. There isn't. Both observers' perceptions are equally legitimate. How you define reality is relative to the perspective from which you measure it. That is what "relativity" means.

So, would a fair analogy be comparing watching a Star Trek show with a chronology of the franchise. If I'm watching the show, I can fast forward and rewind within the specific episode, but can't see what happens beyond the scope of it, whereas, if I'm looking at the chronology, I can see every thing that happened in the franchise before and after. (To put it another way, would your "objective" viewpoint being like seeing the entire chronology of the Universe from beginning to end laid out on one big graph?)

Basically.

Another question, can this big picture assumption be viewed in its entirety from any point? Say, for example that a Trek character, say Rain Robinson from 1997 was shown the big picture from her home time. Would she be able to see everything, or would stuff that happened in her future not be visible to her?

If you step outside of time, you have to stop using concepts like "past" and "future" altogether. Everything is simultaneous. Everything is now. Past and future are just different parts of the unified whole. You're still trapped by your unwillingness to question your own core assumptions, the definitions of the terms you're using, so you can't even ask the right questions.

So, you can't rewind and skip the time that the "process of change" by jumping from say your present, to spending five weeks in the past, and then returning to the exact moment you left in the present again?

You're still completely failing to get it. You're not even trying.

But the reality of the events don't change, anymore than the directions of East and West not changing, regardless of which is behind you. Or is that not important to this model?

There is no superior "reality" that is absolutely right. You need to stop assuming that there is. Measurements of time, space, and physical processes are relative to the reference frame of the observer. We invent labels like east/west or past/future to give us a common framework for communication, so that we can understand how our relative perceptions relate to each other, but that doesn't mean the framework is the absolute Truth.

 

[WebLurker]

Not "illusory," because that implies it's unreal and that there's a superior, "true" perception. There isn't. Both observers' perceptions are equally legitimate. How you define reality is relative to the perspective from which you measure it. That is what "relativity" means.

Okay.

Basically.

Good to know. I think your model makes more sense now.

If you step outside of time, you have to stop using concepts like "past" and "future" altogether. Everything is simultaneous. Everything is now. Past and future are just different parts of the unified whole.

Okay.

You're still trapped by your unwillingness to question your own core assumptions, the definitions of the terms you're using, so you can't even ask the right questions.[/quotes]

I'm still trying to get a grasp on the basics here, esp. since I was never much of a science person back in school.

You're still completely failing to get it. You're not even trying.

Well, sorry for being willing to ask stupid questions in the hopes of getting a better handle on things, rather than choosing to appear smarter and not saying anything.

There is no superior "reality" that is absolutely right. You need to stop assuming that there is. Measurements of time, space, and physical processes are relative to the reference frame of the observer. We invent labels like east/west or past/future to give us a common framework for communication, so that we can understand how our relative perceptions relate to each other, but that doesn't mean the framework is the absolute Truth.

So, "your eyes can deceive you; don't trust them", then? Well, say if reality is as relative as all that, is there anything out there we can take as absolute?

 

[Markonian]

So, Pegg's statement would allow for the NX-like Archon to exist.

 

[Christopher]

So, Pegg's statement would allow for the NX-like Archon to exist.

From the comics, you mean? Theoretically, I suppose. Although that story's divergences from the original episode are a bit hard to rationalize even with the retroactive-alteration theory.

 

[Idran]

So, "your eyes can deceive you; don't trust them", then? Well, say if reality is as relative as all that, is there anything out there we can take as absolute?

In terms of space and time? No. That was the big discovery of relativity; that it isn't just speed that changes according to the reference frame of the observer, but spacetime itself. Distances in both space and time vary according to the observer's speed relative to the speed of the two things you're measuring the distance between. That's what causes things such as length contraction (the faster something goes relative to you, the more it shrinks along the direction of travel) and time dilation (the faster something goes relative to you, the slower time passes for it) as your speed changes. And there is no preferred reference frame; any reference frame where you're not in the process of changing speed is equally as valid as any other, and there literally is no such thing as absolute space or absolute time.

And it's not a question of such things simply appearing to change as your reference frame changes either; they literally do change, it's a fundamental property of spacetime.

For example, muons are a type of short-lived particle generated when cosmic rays hit the atmosphere. The half-life of muons is about 1.5 microseconds. It takes about 34 microseconds for a muon to travel from the top of the atmosphere to a ground station to be detected, meaning that out of every 10,000,000 muons generated, we should only detect 3. However, when we actually measured the number, out of every 10,000,000 muons that should have been generated based on our calculations of the rate of generation, we measured around 490,000. This is because of time dilation; they move so fast relative to us that time was literally passing more slowly for them from our perspective, which means that to us, they decayed more slowly. (And this isn't a paradox, because from the perspective of the muon, the Earth is moving so quickly towards it that the distance it had to travel was shorter because of length contraction.)

GPS satellites are another great example. They need to have precise timing for GPS to function, down to the smallest fractions of seconds. They need to be so precise that, even though they aren't really moving all that quickly relativistically speaking (14,000 km/hour, or about .000013 times the speed of light), we actually need to account for the slight time dilation between us and them in their software to keep them properly synchronized to Earth-based clocks.

 

[Christopher]

GPS satellites are another great example. They need to have precise timing for GPS to function, down to the smallest fractions of seconds. They need to be so precise that, even though they aren't really moving all that quickly relativistically speaking (14,000 km/hour, or about .000013 times the speed of light), we actually need to account for the slight time dilation between us and them in their software to keep them properly synchronized to Earth-based clocks.

Indeed, I believe that's a feature, not a bug. Keeping track of the subtle relativistic differences between the satellites' onboard clocks is part of how they determine their position and motion relative to each other and thereby have a reference for computing positions on the ground, or so I gather. So we actually use relativistic phenomena on a daily basis in everyday life, thanks to GPS.

 

[Idran]

Indeed, I believe that's a feature, not a bug. Keeping track of the subtle relativistic differences between the satellites' onboard clocks is part of how they determine their position and motion relative to each other and thereby have a reference for computing positions on the ground, or so I gather. So we actually use relativistic phenomena on a daily basis in everyday life, thanks to GPS.

In two different ways, even. GPS satellites not only have to account for relativistic time dilation due to orbital speed, but also gravitational time dilation due to being higher in Earth's gravitational well. There's a good description of it here.

For a low earth orbiter such as the Space Shuttle, the velocity is so great that slowing due to time dilation is the dominant effect, while for a GPS satellite clock, the gravitational blueshift is greater. The effects cancel at

.

This is also a great chart from that same article that sums up the impact, calculating the overall time shift from the two effects for various altitudes (since both orbital speed of a circular orbit and gravitational blueshift are both based almost wholly on altitude).

For a GPS satellite specifically, time dilation slows onboard clocks (relative to us) by about 7 microseconds/day, and gravitational blueshift speeds onboard clocks by about 45 microseconds/day. If it wasn't accounted for, that overall speeding up of 38 microseconds/day would add up to about an additional 11km error in positioning every day.

 

[WebLurker]

In terms of space and time? No. That was the big discovery of relativity; that it isn't just speed that changes according to the reference frame of the observer, but spacetime itself. Distances in both space and time vary according to the observer's speed relative to the speed of the two things you're measuring the distance between. That's what causes things such as length contraction (the faster something goes relative to you, the more it shrinks along the direction of travel) and time dilation (the faster something goes relative to you, the slower time passes for it) as your speed changes. And there is no preferred reference frame; any reference frame where you're not in the process of changing speed is equally as valid as any other, and there literally is no such thing as absolute space or absolute time.

And it's not a question of such things simply appearing to change as your reference frame changes either; they literally do change, it's a fundamental property of spacetime.

For example, muons are a type of short-lived particle generated when cosmic rays hit the atmosphere. The half-life of muons is about 1.5 microseconds. It takes about 34 microseconds for a muon to travel from the top of the atmosphere to a ground station to be detected, meaning that out of every 10,000,000 muons generated, we should only detect 3. However, when we actually measured the number, out of every 10,000,000 muons that should have been generated based on our calculations of the rate of generation, we measured around 490,000. This is because of time dilation; they move so fast relative to us that time was literally passing more slowly for them from our perspective, which means that to us, they decayed more slowly. (And this isn't a paradox, because from the perspective of the muon, the Earth is moving so quickly towards it that the distance it had to travel was shorter because of length contraction.)

GPS satellites are another great example. They need to have precise timing for GPS to function, down to the smallest fractions of seconds. They need to be so precise that, even though they aren't really moving all that quickly relativistically speaking (14,000 km/hour, or about .000013 times the speed of light), we actually need to account for the slight time dilation between us and them in their software to keep them properly synchronized to Earth-based clocks.

Indeed, I believe that's a feature, not a bug. Keeping track of the subtle relativistic differences between the satellites' onboard clocks is part of how they determine their position and motion relative to each other and thereby have a reference for computing positions on the ground, or so I gather. So we actually use relativistic phenomena on a daily basis in everyday life, thanks to GPS.

In two different ways, even. GPS satellites not only have to account for relativistic time dilation due to orbital speed, but also gravitational time dilation due to being higher in Earth's gravitational well. There's a good description of it here.



This is also a great chart from that same article that sums up the impact, calculating the overall time shift from the two effects for various altitudes (since both orbital speed of a circular orbit and gravitational blueshift are both based almost wholly on altitude).

For a GPS satellite specifically, time dilation slows onboard clocks (relative to us) by about 7 microseconds/day, and gravitational blueshift speeds onboard clocks by about 45 microseconds/day. If it wasn't accounted for, that overall speeding up of 38 microseconds/day would add up to about an additional 11km error in positioning every day.

I really feel like I'm in over my head here.

 

[Mr. Laser Beam]

^ I think I need Dramamine. Or at least a bottle of gin.

 

[Idran]

Not sure if I should add the big thing I referenced earlier, then, but I will anyway.

That thing about distances in space and time varying based on your speed? For the time side, the distance doesn't always have the same sign either.

That is, if two events are far enough apart in spacetime that light can't go from one to the other, meaning that there can't be any cause-effect connection between them (called a "space-like separated interval" if you want to know the physics term), then the order that they happen in? Isn't fixed. It varies based on your speed too. Not that it can vary, but for any possible amount of time that can pass between them, positive or negative, there is a velocity vector at which they are that far apart in time. And that means that two events that are simultaneous in one reference frame aren't simultaneous in another reference frame (since two precisely simultaneous events would by definition fall under that first condition unless they happened at exactly the same point in space as well). If two stars are measured to blow up at precisely the same moment from the perspective of Earth, then there's a velocity vector where star A blew up a year before star B, and a velocity vector where star B blew up a year before star A. Not an illusion of the travel time of light either; I mean even when accounting for that, the actual time at which the event is measured to happen by you.

And a natural consequence of this is that there is no such thing as a universal "present" either.

Exploiting this is essentially why FTL is equal to time travel in real life. It is literally impossible by real-life physics to have any sort of FTL travel that doesn't break causality, because the two are logically equivalent under relativity.

(Less mind-blowing but still interesting: if two events could have a causal relationship between them because the spacetime distance between them is short enough that light could travel from one to the other [called a "time-like separated interval"], then you can never see them happen at the same point in time, but there is a velocity vector where they happen at the same point in space relative to you. Which may actually seem a little obvious if you think what that means; it means literally the point where you measure it to be relative to your current location and nothing else.)

 

[WebLurker]

Not sure if I should add the big thing I referenced earlier, then, but I will anyway.

That thing about distances in space and time varying based on your speed? For the time side, the distance doesn't always have the same sign either.

That is, if two events are far enough apart in spacetime that light can't go from one to the other, meaning that there can't be any cause-effect connection between them (called a "space-like separated interval" if you want to know the physics term), then the order that they happen in? Isn't fixed. It varies based on your speed too. Not that it can vary, but for any possible amount of time that can pass between them, positive or negative, there is a velocity vector at which they are that far apart in time. And that means that two events that are simultaneous in one reference frame aren't simultaneous in another reference frame (since two precisely simultaneous events would by definition fall under that first condition unless they happened at exactly the same point in space as well). If two stars are measured to blow up at precisely the same moment from the perspective of Earth, then there's a velocity vector where star A blew up a year before star B, and a velocity vector where star B blew up a year before star A. Not an illusion of the travel time of light either; I mean even when accounting for that, the actual time at which the event is measured to happen by you.

And a natural consequence of this is that there is no such thing as a universal "present" either.

Exploiting this is essentially why FTL is equal to time travel in real life. It is literally impossible by real-life physics to have any sort of FTL travel that doesn't break causality, because the two are logically equivalent under relativity.

(Less mind-blowing but still interesting: if two events could have a causal relationship between them because the spacetime distance between them is short enough that light could travel from one to the other [called a "time-like separated interval"], then you can never see them happen at the same point in time, but there is a velocity vector where they happen at the same point in space relative to you. Which may actually seem a little obvious if you think what that means; it means literally the point where you measure it to be relative to your current location and nothing else.)

That is very cool and very confusing.