Hermione learns a thing

[Aineko]

Going backwards in time requires looping one's light cone. Simple acceleration won't do that, no matter whether you're doing stuff with FTL or STL travel. And even wormhole creation can only take you as far back as the initial creation of the wormhole.

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Go someplace FTL. Accelerate a bunch back in the direction you came from in normal space, tilting your relative space/time reference frame. Go FTL back that way. If you've combined sufficient delta-V and sufficient FTL, you should now be sitting inside the historic light cone of your original departure.

EDIT: I might have the direction of acceleration you want backwards. I'd need some time to check that. Towards or away, one of the two...

Late edit 2: I think it should be away. Going in a direction tilts your space axis in that direction towards your future light and thus the opposite direction towards your past light (from the pre-acceleration perspective) . And it's the tilt towards past light that makes your FTL jaunt go backwards with respect to the target's time.

 

[Sandy River DL]

Go someplace FTL. Accelerate a bunch back in the direction you came from in normal space, tilting your relative space/time reference frame. Go FTL back that way. If you've combined sufficient delta-V and sufficient FTL, you should now be sitting inside the historic light cone of your original departure.

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Returning to your original light cone isn't going back in time. Because what you're missing is the elapsed time of the set-up and the fact that FTL still takes time, even teleportational methods.

 

[Aineko]

Returning to your original light cone isn't going back in time. Because what you're missing is the elapsed time of the set-up and the fact that FTL still takes time, even teleportational methods.

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Historic lightcone, not forward light cone. Your historic light cone is your past.

FTL having a finite speed and needing time to perform steps just increases the scale you need, it doesn't break the logic.

 

[Sandy River DL]

Historic lightcone, not forward light cone. Your historic light cone is your past.

FTL having a finite speed and needing time to perform steps just increases the scale you need, it doesn't break the logic.

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Let's say you have an instantaneous teleportation drive that can cross the Universe. You then trigger it twice. A bare minimum of four plank temporal units have passed. So you're still arriving after you left even with the absolute fastest FTL possible. And likely much longer, as very few processes take that little time.

TL;DR, the only part of your light cone you can get to by moving, is the forward light cone.

 

[DestinyPlayer]

One thing I never quite got is how is all of that light bullshittery even time travel? Isn't it just, well, the equivalent of walking over your footprints, where you are not interacting with yourself from the past, you are merely interacting with the aftereffects of you having been there in the past? Where meeting your own light will be merely meeting a mirage of yourself from the past rather than actually facing yourself from the past?

 

[Aineko]

Let's say you have an instantaneous teleportation drive that can cross the Universe. You then trigger it twice. A bare minimum of four plank temporal units have passed. So you're still arriving after you left even with the absolute fastest FTL possible. And likely much longer, as very few processes take that little time.

TL;DR, the only part of your light cone you can get to by moving, is the forward light cone.

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If you live in a non-relativistic universe, that logic would hold weight.

But since you don't, time isn't the same thing from all points of view. That's why in my instructions, you change velocity between FTL transfers. By doing so, you change what space and time are to you, to make your pre-jump historic light cone intersect your 'present' hypersurface. Then you jump there.

One thing I never quite got is how is all of that light bullshittery even time travel? Isn't it just, well, the equivalent of walking over your footprints, where you are not interacting with yourself from the past, you are merely interacting with the aftereffects of you having been there in the past? Where meeting your own light will be merely meeting a mirage of yourself from the past rather than actually facing yourself from the past?

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Once you're inside your historic light cone, that means you are in a place where it is possible to interact with your historical self.

Depending how far back, obviously, you might have to wait a bit.

You could describe your historic light cone as the slice of the universe from which somebody could kill you with a big enough gun...

 

[sdwood]

You need some very, very expensive machinery that is utterly reliant on a century of hard work from thousands of scientists and another century of theory on top of that.

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This is almost true.

You need very, very expensive machinery that is utterly reliant on a century of hard work from thousands of scientists _telling everyone what they've learned_, and then another century of openly spread theory on top of that.

Fifty years after Hermione goes to Hogwarts, the magical world will be divided into two parts.

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No, it has to be three.

"Gallia est omnis divisa in partes tres"

I'm absolutely certain she's referring to the time travel. Relativity, causality, FTL; pick two.

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Nope. Einstein missed something, probably something that couldn't be detected or predicted at the time.

Admittedly, that's a religious belief on my part (I don't believe God would create the rest of the universe if he never intended for us to get there), so I'm not going to try to convince anyone else.

I'd like to think my first experience with a TARDIS wouldn't be "it's larger/smaller on the...", I'd like to think I'd do something along the lines of "Ooooo, dimensionally remapped space. It looks like you packed up your house and took it with you. But why does it look like an old police call box?"

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Because the Chameleon Circuit is broke. Surely that would be obvious at first glance, as that would be the only reason it didn't blend in.

Hermione: Opening door before the knock - "Hello, please do come in. I've felt you coming for few minutes. I've been hoping to meet one of you for over a year now. I've got so many questions..."
Minerva: "Hello Ms. Granger, I'm here to..., wait a..., what???!"

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More like, "I've been wanting to meet you in specific for a couple of years."

Edit: To be clear, the Romans would pour goat and other sacrificial blood on their concrete toward the tail end of curing, and we've found that for some reason adding iron suspended in something at that part really does help. Though you can just mix in iron particles while it's mixing, it doesn't seem to be quite as effective for reasons related to how the material forms. But adding the Iron-Liquid to semi-porous concrete fills in some of the gaps.

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How much blood did they use? I find it unlikely they used enough to matter.

 

[DestinyPlayer]

Once you're inside your historic light cone, that means you are in a place where it is possible to interact with your historical self.

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The thing I don't get is why is that considered to be true? There is probably something I am missing, but the direct line of logic that I see is that being inside your historic light cone merely means that you see the light of yourself from the past. See, not interact with. It is merely the afterimage of yourself from the past going so fast you're leaving imprints, and the more likely situation to me is that space is going to get very light polluted with everyone's trails rather than time travel.

 

[FourmyleOfCeres]

How much blood did they use? I find it unlikely they used enough to matter.

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Uncertain, but it only really seemed to be a surface protection. Still useful. And has been replicated several times in the 90s. If you could find a way to get it to penetrate deeper, you could definitely get a greater effect, but it does make the outside harden better.

Edit: Which makes it useful for steps and anything else that would see a lot of traffic and wear.

 

[Sandy River DL]

If you live in a non-relativistic universe, that logic would hold weight.

But since you don't, time isn't the same thing from all points of view. That's why in my instructions, you change velocity between FTL transfers. By doing so, you change what space and time are to you, to make your pre-jump historic light cone intersect your 'present' hypersurface. Then you jump there.

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I don't think you grasp what kinds of relativistic effects you're talking about. Like, experiments have been run on how acceleration affects the flow of time, and from my understanding all accelerating a FTL vessel would do is lengthen the second trip. While I'm not able to do math at that level, I'm pretty sure going back in time requires either something to occur in negative plank time, or space-time being twisted into a loop. Going FTL inside a black hole might do it, but not STL relativistic effects paired with FTL travel.

 

[Aineko]

The thing I don't get is why is that considered to be true? There is probably something I am missing, but the direct line of logic that I see is that being inside your historic light cone merely means that you see the light of yourself from the past. See, not interact with. It is merely the afterimage of yourself from the past going so fast you're leaving imprints, and the more likely situation to me is that space is going to get very light polluted with everyone's trails rather than time travel.

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You're thinking about the wrong light cone there.

The historic light cone is your past: it is the set of places in spacetime from which something could get to where you are in the present without exceeding the speed of light. (Technically the light cone I think is the outer surface, the places from which something reaches you at exactly the speed of light, and the part of the past that's more 'useful' is what is inside of that surface.) Wherever you were five minutes ago, there-five-minutes-ago is inside your historic light cone. Unless you've been going FTL since then.

The forward light cone of your past self is a totally different thing. Using a single FTL hop to look into the past by viewing old light isn't time travel, at least from a frame of reference you're interested in.

 

[drvash]

quantum physics

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QUESTION:
How much of a leap would it be for Hermione to contemplate Protean-style quantum entanglement?

The kind where items are magically linked together like the D.A. coins and Voldemort's Dark Mark?

Not sure if animated portrait's ability to visit other frames comes from the Protean charm, or if the Floo Network uses a similar method to facilitate transportation between fireplaces.

 

[Aineko]

I don't think you grasp what kinds of relativistic effects you're talking about. Like, experiments have been run on how acceleration affects the flow of time, and from my understanding all accelerating a FTL vessel would do is lengthen the second trip. While I'm not able to do math at that level, I'm pretty sure going back in time requires either something to occur in negative plank time, or space-time being twisted into a loop. Going FTL inside a black hole might do it, but not STL relativistic effects paired with FTL travel.

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There's one thing I may be getting wrong, but it isn't that.

But you're consistently talking as if time is a single axis. The critical point in play is that it isn't.

This is a job for Minkowski diagrams more than breaking out formulas, from my also-not-a-physicist perspective. I've seen a nice website that lays those out but I'm failing to find it now - google prefers some hard-to-read pencil diagrams over the clean ones I've seen before.

 

[Sandy River DL]

There's one thing I may be getting wrong, but it isn't that.

But you're consistently talking as if time is a single axis. The critical point in play is that it isn't.

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Um, time is a single axis. Because time is a single dimension. What you're thinking of is how movement through the three spatial dimensions affects the rate of travel along the temporal dimension.

 

[Rathmun]

Moving faster than light "time travel" is not the same as the "oops, paradox!" time travel people think of when they say time travel.

Exiting your light cone does not cause a paradox, it causes you to be in a place that the light from your previous location would not be able to reach. That's it. If you've got an FTL drive that can move at 10x the speed of light called the "NEEP" drive, then you've replaced your light-cone with a NEEP-cone, which is flatter than the light cone, but it's still a cone. Causality is still preserved, the only "travel" in time that you've done is to go slightly faster or slower into the future that you were already time travelling towards just by existing in 4-space.

Things that are not travelling in time exist to us for one unit of plank-time, and then we've gone past them, because we are all already travelling in time.

Now wormholes - those are potential paradox type time travel, they leave 4-space, and pop back in potentially anywhere else, including right behind you ten minutes ago. (edit: weird typos)

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No, exiting your light cone at all is sufficient for time travel. Even if your drive is only capable of 1.01c, it's enough.

In the interests of not drawing the space time diagrams myself, I'm going to reference PBS spacetime again.

View: https://www.youtube.com/watch?v=HUMGc8hEkpc
Naturally, Dr. O'Dowd points out that FTL paths that go back in time aren't real. (Well, as far as we know anyway.)

The issue is that the speed of light is the speed of causality. Light happens to travel at that speed because it's massless, but the speed of light isn't actually about light. If you manage to go faster, you're outracing cause-and-effect. You can arrange for something to happen in such a way that, to all observers, it happens before the thing that first caused it.

 

[Aineko]

Um, time is a single axis. Because time is a single dimension. What you're thinking of is how movement through the three spatial dimensions affects the rate of travel along the temporal dimension.

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Nope, that's the key thing here. In four-dimensional space time, there isn't one true time. Simultaneity in relativistic space is a matter of point of view. There is no such thing as true time.


Or for another angle, the rate of travel along the temporal dimension in terms of what?

 

[Sandy River DL]

Nope, that's the key thing here. In four-dimensional space time, there isn't one true time. Simultaneity in relativistic space is a matter of point of view. There is no such thing as true time.


Or for another angle, the rate of travel along the temporal dimension in terms of what?

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In Einsteinian space-time, time is like length. That is, it is a variable axis that describes an attribute. For example, time on Earth is different from time on Jupiter, but both have time just like they both have a diameter. That they have different time and diameters is irrelevent to the fact that they have those attributes. Time being a singular axis has nothing to do with simultaneity.

 

[suicidejunkie]

While time may be a single dimension, it isn't pointing in the same direction for everybody. When you accelerate, you change your axes. And with that, it becomes simple geometry to show you can go along a closed loop path to visit yourself before you left when you allow FTL speed amounts of axis tilting.

 

[WheeledWriter]

Sounds like you're suggesting 'muggles' (maybe all humanity, including magicals) are related to Deep Ones. I suppose you could mix this in with the magicals having the 'blood of Yig' (Father of Serpents), which might explain parseltongue.

I'm reasonably sure our musically mathematical author does plan a Lovecraftian cross-over for HLaT...

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Well, I wasn't getting that complex.

I was just playing with languages a bit and suggesting that there might be a practical tradition for the inefficency Hermione is observing - i.e that 'noisy' magic comes across as a more natural phenomon - something like white noise or the sound of the universe or whatever.
Whereas efficent magic is like a radio signal - clearly orderly and artifical - and thus attractive to certain types of "Very Bad Things 'Wot Man was Not Meant to Know Of" on account of the fact that it's basically a sign announcing mealtime (think 'the torch in the dark forest' theory of why we aren't getting any ET communication).

This is something which has been very carefully 'forgotten' except by Unspeakables and such that keep tabs on anything that might encourage wizards from doing anything outside of traditional methods - or finding out about the real reasons why things are done the way they are - mostly because whenever anyone finds out (that hasn't been carefully vetted), some idiot always thinks reaching out to Bad Things is a splendid idea.

Tradition is the best way to keep people doing things the 'safe' way regardless of their logic, after all.

The 'fish tail' thing was meant to be an insult (equiv. to 'idiot') that Wizards use to refer to the founder of the Scientific Method whose ideas of methodical study and experimentation started this whole Physical Alchemy (what we call Science) idea that all the non wizards picked up and started using to experiment with stuff wizards know is better left alone. In Latin 'Fish Tailed' translates to 'Mullet' which shifted into 'Muggle' eventually.

So that's why Wizards call people using Aristotle's methods 'muggles'. Though the average wizard doesn't know that history anymore, as that knowlege has been carefully 'forgotten' too. They just know that non-wizards are muggles and they are not.

 

[Aineko]

In Einsteinian space-time, time is like length. That is, it is a variable axis that describes an attribute. For example, time on Earth is different from time on Jupiter, but both have time just like they both have a diameter. That they have different time and diameters is irrelevent to the fact that they have those attributes. Time being a singular axis has nothing to do with simultaneity.

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Time is indeed like length: both of them are matters of perspective. That's basic special relativity!

When you say time is an attribute of Earth vs. Jupiter, it sounds like you're talking about the time axis from a particular frame of reference. But our scenario doesn't involve a single unchanging frame of reference, which is key to the whole exercise.


EDIT: I hate this as an animated gif instead of a page with multiple static images, but this does seem to illustrate what I'm talking about:

Reddit - Dive into anything

www.reddit.com

 

[Sandy River DL]

Time is indeed like length: both of them are matters of perspective. That's basic special relativity!

When you say time is an attribute of Earth vs. Jupiter, it sounds like you're talking about the time axis from a particular frame of reference. But our scenario doesn't involve a single unchanging frame of reference, which is key to the whole exercise.


EDIT: I hate this as an animated gif instead of a page with multiple static images, but this does seem to illustrate what I'm talking about:

Reddit - Dive into anything

www.reddit.com

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I'm confused as to how any of the pre-edit stuff contradicts what I said. As for the whole 'existing the light cone is time travel' stuff, I'm pretty sure that's only for real space FTL, which is impossible under Einsteinian physics. FTL methods like hyperspace aren't covered by that and may or may not be possible, on the basis of us knowing we are missing stuff and there being gaps in Einsteinian physics.

 

[Aineko]

I'm confused as to how any of the pre-edit stuff contradicts what I said.

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I'm confused as to what you said, I think. You seem to be simultaneously saying that time is a singular axis and that different...planets, and I really don't know why planets, have different times. Your analogy suggests that the latter time is referring to a measurement, rather than an axis, which is bewildering in its own right (what's the time measurement of a planet refer to?) and seemingly irrelevant, since quantities of time aren't really at issue here.

So in confusion, I go back a step. There's no unified time. When you talk about how something takes ever so many plank times, that statement means nothing without an attached frame of reference. And picking an outside frame of reference and sticking to it invalidates the presumption that you can't see something apparently have a negative duration.

As for the whole 'existing the light cone is time travel' stuff, I'm pretty sure that's only for real space FTL, which is impossible under Einsteinian physics. FTL methods like hyperspace aren't covered by that and may or may not be possible, on the basis of us knowing we are missing stuff and there being gaps in Einsteinian physics.

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So long as you're traveling to and from real space, I don't care what happens during the FTL transfers and neither does any of what I've brought up.

 

[Sandy River DL]

I'm confused as to what you said, I think. You seem to be simultaneously saying that time is a singular axis and that different...planets, and I really don't know why planets, have different times. Your analogy suggests that the latter time is referring to a measurement, rather than an axis, which is bewildering in its own right (what's the time measurement of a planet refer to?) and seemingly irrelevant, since quantities of time aren't really at issue here.

When you talk about how something takes ever so many plank times, that statement means nothing without an attached frame of reference. And picking an outside frame of reference and sticking to it invalidates the presumption that you can't see something apparently have a negative duration.

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Massive objects slow the flow of time, as demonstrated with the atomic clocks on GPS satellites and on the Earth's surface. Therefore, an object has time like it does a length.

Planck* time, meanwhile, is derived from the Planck Constant and light speed. As it is defined by two constants, your speed doesn't alter it anymore than going faster changes light's speed. No known macroscopic and few quantum phenomenon occur anywhere near that fast, and the only phenomenon I know of that happens faster is virtual pair production.

*Misremembered the spelling.

So long as you're traveling to and from real space, I don't care what happens during the FTL transfers and neither does any of what I've brought up.

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The whole idea of a light cone flat out doesn't work properly for things that don't exist exclusively in real space. Hell, it doesn't work properly for dark matter. Or any of the theoretical particles with velocities measured with imaginary numbers.

 

[Aineko]

Massive objects slow the flow of time, as demonstrated with the atomic clocks on GPS satellites and on the Earth's surface. Therefore, an object has time like it does a length.

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Time is measured in seconds. What does 'jupiter is 8 seconds' mean?

Planck* time, meanwhile, is derived from the Planck Constant and light speed. As it is defined by two constants, your speed doesn't alter it anymore than going faster changes light's speed. No known macroscopic and few quantum phenomenon occur anywhere near that fast, and the only phenomenon I know of that happens faster is virtual pair production.

*Misremembered the spelling.

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Putting aside for the moment that you're trying to mix quantum and relativity and that's well known to run into problems.

I'm not saying that I can make something happen in a more infinitesimal amount of time than that. I am saying that given an FTL device I can make something happen last week. (Well an FTL device and the means to perform changes of velocity that are significant fractions of the speed of light.) And that statement has no dependency on how long it takes to operate the FTL device.

(If you give me an FTL device with enough limitations I might need more than one of them, possibly?)

The whole idea of a light cone flat out doesn't work properly for things that don't exist exclusively in real space. Hell, it doesn't work properly for dark matter. Or any of the theoretical particles with velocities measured with imaginary numbers.

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I have zero knowledge of what an imaginary velocity means, so no comment there.

Not interacting with light is irrelevant. It's a light cone because, as @Rathmun said, light is the speed of causality. Not because we actually care about photons.

I can't even guess what you think the (dis)connection between 'not existing exclusively in real space' and light cones is.

 

[Quickshot0]

Returning to your original light cone isn't going back in time. Because what you're missing is the elapsed time of the set-up and the fact that FTL still takes time, even teleportational methods.

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Considering this discussion from you is still ongoing, I think you'd do really well if you haven't already to first really look at the handy video posted on FTL travels link to time travel. But to save you to have to look for the link in the post history, I'll relink it for you here.

The video gives a fairly in-depth look of the matter, rather then just some pop-sci answer, going in to more serious depths on the matter.


I think this would be more constructive, because at that point you'd at least understand far better what exactly the others are arguing and why many of your current arguments have little chance to sway them.


Now having said all that, I'm not entirely willing to throw out FTL travel as totally impossible for sure. How ever this requires making some kind of compromise on what we think constitutes reality, and not the trivial sort of compromise. It is so far I can tell unavoidable that one has to give up on some important element of reality we take as true. for it to be possible... So well the cuts will hurt you somewhere I guess.

In any case, a fair few physicists don't think for now there is evidence that one of our central pillars on reality is false. Because well we think reality is the way it is for a reason after all, it really seems to work that way.


Still to give you an example on how you can have FTL and is also relevant to this story, is to have time travel be possible. But this isn't a trivial decision, if it's possible in one way, it's probably true in many ways. To the extent that you'd probably get something like retro-causality, where the past determines the future and the future determines the past, it's all interlinked and in a sense all of time is perhaps already set. You still make your choices, as does everyone else, but the conclusion of all those choices made of ones own will is still already known and there is nothing one can do to change it. After all, any kind of time travel in reality is already incorporated in reality, time travel changes nothing. Everything will happen, has already happened, what is time even really anyway?

Well pick ones poison in the end I guess.