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Story Wednesday, July 3rd, 2019

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26 minutes ago, Darth Fluffy said:
2 hours ago, hkmaly said:

As a bonus, if you create a wormhole, then take one end on circular tour with relativistic speed, when you return, you WILL have a time machine allowing you to send stuff into past (but not before creating the wormhole obviously). See Xeelee Sequence by Stephen Baxter.

Sure, sure, we have a plan, trivially easy, we leave it as an exercise for the students, who hopefully have exotic matter to keep it open ...

Students are inventive. If you don't tell them it's impossible, sooner or later someone will discover it just to get better grade.

27 minutes ago, Darth Fluffy said:
2 hours ago, hkmaly said:

Thing is that in quantum physics, causality ALREADY doesn't work how would you expect. Electron can interfere with itself. Grandfather paradox is obviously impossible, but that doesn't mean time travel is - it just means that when the waveform collapses, every effect will have it's cause.

At a quantum level, sure. A positron might be an electron moving back in time, it would look the same; entropy barely holds with very small numbers and quantities. But scale it up, and it falls apart quickly.

Reminds me one short story ... some physicist was very proud because he computed that it's impossible to keep force field stable for significant fraction of second. Some engineer meanwhile developed force field generator based on quickly turning the field on and off, multiple times per second. The force field was not there part of the time, but it was STILL airtight and capable of holding pressure of earth atmosphere.

You can never know if there is some loophole allowing to scale something up in useful manner until you try.

32 minutes ago, Darth Fluffy said:

Something other than normal "stuff" is filling up most of the universe.

That's usually called dark matter, but yes: we don't know what it is, can be useful.

33 minutes ago, Darth Fluffy said:

Not sure about black hole nudity. It's based on spin, and I don't get why starting with the angular momentum of a star, as the object collapses to zero size, the rotational speed should be effectively infinite to maintain that angular momentum (think skater bringing their arms in), but apparently that's not the case.

The trick is that while the star collapses, it's throwing away lot of matter and light. Black hole will form if the remains of stars is about three times the mass of Sun, but the original stars needs to be like TWENTY times bigger to get over the limit.

36 minutes ago, Darth Fluffy said:

My theory is time travel is easy, but every timeline that discovers it is inherently unstable, so only the ones where it's never discovered remain.

That is indeed possible. It's also possible that timelines discovering time travel are not INHERENTLY unstable but just statistically more likely unstable.

In short, it is possible time travel will be discovered, used and then lost in incident looking less likely than several time-travel movies ... because just that single time, the seemingly absurd scenario with time travel will be more probable that never discovering time travel at all.

Note that based on every day experience, time travel to today will never work reliably. You can verify that by going to any memorable public event and counting people who obviously don't belong to our time: if there would be reliable time travel to our time, the number will be bigger than how many people are currently on Earth, because even if there will be just one historian from every century since building a time machine to thermal death of universe ...

However, besides time travel not being possible, there are several other ways how specifically time travel to TODAY will not work.

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Lots of hypothetical methods of time travel (e.g. wormholes) have the limitation that they can not send anything back to before the time-travel-enabling device itself first became active. In other words, you could not reach back to open a time warp at an arbitrary past time, but once the time warp is open, you can visit it from any arbitrary future time.

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12 minutes ago, hkmaly said:

The trick is that while the star collapses, it's throwing away lot of matter and light. Black hole will form if the remains of stars is about three times the mass of Sun, but the original stars needs to be like TWENTY times bigger to get over the limit.

Good point, if the collapsing star throws away matter, it's also shedding angular momentum, but not more than the proportion of mass it's shedding, so your huge star that shed 85% of it's mass still has 15% of it's angular momentum. In a space with zero width.

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6 hours ago, Darth Fluffy said:

Good point, if the collapsing star throws away matter, it's also shedding angular momentum, but not more than the proportion of mass it's shedding, so your huge star that shed 85% of it's mass still has 15% of it's angular momentum. In a space with zero width.

Thinking about this, I don't think this limitation is true. Since the mass is violently shed, it should carry away a disproportionate amount of angular momentum. Still, huge to begin with, and zero width. Hmm.

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21 hours ago, Darth Fluffy said:

My theory is time travel is easy, but every timeline that discovers it is inherently unstable, so only the ones where it's never discovered remain.

I wouldn't go so far as to call it easy, but it's quite doable for an advanced enough civilization. In fact, I do it all the time. The thing is, time is like a tree with many branches, and each branch is a timeline. Most of the branch points correspond to events at the quantum scale, but some correspond to points where travelers might or might not arrive from the future, with one or more branches featuring arrivals but at least one branch continuing on without any arrival. (The timeline may branch further based on their actions in the "past" of course.) This means that those who attempt to change history may find themselves in a timeline they don't recognize, but they never actually "changed" anything - their old timeline is still there, "where" it's always been.

The reason why there doesn't appear to have been any temporal tourists/researchers on Earth in recorded history is partially the result of some travelers choosing to blend in with the locals, and partially the result of those who talk about having traveled through time not being believed (you probably don't believe I'm a time traveler, either), but mainly the result of us happening to be in a branch where not many arrivals took place (yet).

OOC: Actually, to be depressingly down to earth, I think it most likely that travel "backwards" in time is only possible at the quantum scale and even at that scale no useful information can make the journey.

However, that's no fun, so I'm hoping something like what I said above it true. The Many Worlds Interpretation of quantum mechanics seems like a promising way to provide the right kind of multiverse for it, and as a bonus I also think it makes a lot more sense than Copenhagen Interpretation. And having entering the past be a quantum branching event not only provides a possible solution to the lack of time tourists (as alluded to above), but also solves the issue of the Grandfather Paradox.

I am also rather fond of the idea that people can travel through time within a single timeline, but that history cannot be altered... However, while this may prevent the Grandfather Paradox, it doesn't really solve the problem of time tourists (unless you're satisfied with the answer "history said they weren't there, so they weren't able to be there", but I'm not satisfied with that). (Of course, the solution could be in the method of time travel rather than the theory - for instance, if as ijuin mentioned above the time machine cannot send you back before it's creation.)

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1 hour ago, ChronosCat said:

The reason why there doesn't appear to have been any temporal tourists/researchers on Earth in recorded history is partially the result of some travelers choosing to blend in with the locals, and partially the result of those who talk about having traveled through time not being believed (you probably don't believe I'm a time traveler, either), but mainly the result of us happening to be in a branch where not many arrivals took place (yet).

Hmm, that's sort of like Hilbert's Hotel--there are infinite rooms (branches), so even though there are infinite visitors, there is always space for more.

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6 hours ago, ChronosCat said:

(time travel is easy) In fact, I do it all the time.

Yes, everyone does. 1:1 ratio. Stopping would be a trick.

Also, I replace myself with an exact duplicate, constantly.

But these are not particularly illuminating observations.

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On 7/20/2019 at 11:32 AM, Darth Fluffy said:

Also, I replace myself with an exact duplicate, constantly.

Exact? You are good. I usually get few particles off.

On 7/20/2019 at 11:32 AM, Darth Fluffy said:

Yes, everyone does. 1:1 ratio. Stopping would be a trick.

The ratio is actually 1:c or something. I mean, it's not 1 meter to 1 second.

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23 hours ago, Darth Fluffy said:
On 7/29/2019 at 9:02 PM, hkmaly said:

The ratio is actually 1:c or something. I mean, it's not 1 meter to 1 second.

One second per second.

... right. I was thinking about something else.

Although, wait: if you time travel one second per second, it means there are TWO ways to measure time, two time dimensions. This is actually related to some paradoxes shown in movies. Like, Back to the future: Marty is starting to disappear because past is changing. But wait, why is he starting to disappear? Why didn't he disappeared immediately?

 

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1 hour ago, hkmaly said:

... right. I was thinking about something else.

Although, wait: if you time travel one second per second, it means there are TWO ways to measure time, two time dimensions. This is actually related to some paradoxes shown in movies. Like, Back to the future: Marty is starting to disappear because past is changing. But wait, why is he starting to disappear? Why didn't he disappeared immediately?

Because the movie would have sucked?

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13 hours ago, hkmaly said:

Although, wait: if you time travel one second per second, it means there are TWO ways to measure time, two time dimensions. This is actually related to some paradoxes shown in movies. Like, Back to the future: Marty is starting to disappear because past is changing. But wait, why is he starting to disappear? Why didn't he disappeared immediately?

According to General Relativity, an object's speed affects it's relationship with time; one's perspective can affect how fast objects appear to be moving. So, "one second per second" could mean "My personal clock is measuring the same amount of time passing as a clock in another arbitrary location". Of course this means that how fast you're "traveling through time" depends one what you choose as your reference point!

As for Back to the Future, if the effects of Marty changing history has occurred instantly across the entire timeline, there would have been no Marty to change history, leading to the classic grandfather paradox. My interpretation is that this delay in erasing him from history is a kind of cosmic defense mechanism against paradoxes; the part of Marty's timeline close to the moment of change is preserved so as to allow the new timeline to properly overwrite the old one. ...Or it's just a movie and they cared more about the story being fun and dramatic than it making sense...

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7 hours ago, ChronosCat said:
21 hours ago, hkmaly said:

Although, wait: if you time travel one second per second, it means there are TWO ways to measure time, two time dimensions. This is actually related to some paradoxes shown in movies. Like, Back to the future: Marty is starting to disappear because past is changing. But wait, why is he starting to disappear? Why didn't he disappeared immediately?

According to General Relativity, an object's speed affects it's relationship with time; one's perspective can affect how fast objects appear to be moving. So, "one second per second" could mean "My personal clock is measuring the same amount of time passing as a clock in another arbitrary location". Of course this means that how fast you're "traveling through time" depends one what you choose as your reference point!

Well, everything does, that's the point of theory of RELATIVITY.

But my point was that if you start talking about time travel or even just theory of relativity professionally, you will use terms like world line or timelike curve. "Speed of time travel" is something you can't define in any meaningful way.

7 hours ago, ChronosCat said:

As for Back to the Future, if the effects of Marty changing history has occurred instantly across the entire timeline, there would have been no Marty to change history, leading to the classic grandfather paradox. My interpretation is that this delay in erasing him from history is a kind of cosmic defense mechanism against paradoxes; the part of Marty's timeline close to the moment of change is preserved so as to allow the new timeline to properly overwrite the old one. ...Or it's just a movie and they cared more about the story being fun and dramatic than it making sense...

I'm sure "it's just a movie" is the correct explanation as far as the writers are concerned.

However, you can make a time travel theory with effects like that ... it just require two-dimensional time. One dimension you travel in, and another making the overwriting possible. Like, you said "new timeline overwrites the old one" ... but "old" and "new" are terms related to time. You need some time dimension in which you compare that one of the timelines is older.

(I hope I'm explaining it in way it makes sense ... not exactly easy idea to explain.)

7 hours ago, Pharaoh RutinTutin said:

I believe a conversation between Grace and Tedd regarding some other movie physics is applicable

https://egscomics.com/egsnp/2010-01-27

:)

 

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1 hour ago, hkmaly said:

 "Speed of time travel" is something you can't define in any meaningful way.

It could mean your subjective time vs an external reference, such as events or generations. That's certainly meaningful to you, the traveler.

 

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3 minutes ago, Darth Fluffy said:
1 hour ago, hkmaly said:

"Speed of time travel" is something you can't define in any meaningful way.

It could mean your subjective time vs an external reference, such as events or generations. That's certainly meaningful to you, the traveler.

True. However, that wouldn't be 1:1 then ; depending of what external reference you choose, gravity and movement will modify it.

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1 hour ago, hkmaly said:

True. However, that wouldn't be 1:1 then ; depending of what external reference you choose, gravity and movement will modify it.

Yeah, I don't have that technology. That's why I'm doing the 1:1 thing.

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27 minutes ago, Darth Fluffy said:
1 hour ago, hkmaly said:

True. However, that wouldn't be 1:1 then ; depending of what external reference you choose, gravity and movement will modify it.

Yeah, I don't have that technology. That's why I'm doing the 1:1 thing.

... you don't need any technology to be inside gravitation field. Compared to reference point on Moon, your personal time is slower. Measurably slower. GPS satellites need to compensate both for lower gravity and higher speed compared to Earth's surface.

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1 hour ago, hkmaly said:

... you don't need any technology to be inside gravitation field. Compared to reference point on Moon, your personal time is slower. Measurably slower. GPS satellites need to compensate both for lower gravity and higher speed compared to Earth's surface.

Fair point. 0.999999:1.000000. I met a guy who was making that case back in the late 70s / early 80s. 

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