Interesting physics question

[Bill Phil]

1 minute ago, K^2 said:

This statement should always come with the words "locally" or "in flat space-time".

Fair enough.

[JoeSchmuckatelli]

1 hour ago, K^2 said:

This statement should always come with the words "locally" or "in flat space-time".

Wild Donkeyed Guess - but are you referring to entanglement or some other thing of which I'm blithely unaware?

[Nuke]

the amount of torque you would need to rotate the bar would likely deform it. 

if youve ever worked construction or at least handled a long 2x4 you know that its easier to rotate it along the long axis than the other 2. this is a good example of the concept of moment of inertia as the mass distribution matters. obviously trying to rotate a lightyear long 2x4, you need to accelerate the mass at the end at a faster rate than the mass closer to the center. and obviously that mass at the end cant break the speed of light. assuming perfect rigidity and you ignore any structural issues (and you encounter these at much smaller scales) you will be rpm capped and at a very low value as the ends approach relativistic speeds. at some point you would stop getting appropriate acceleration of the end masses and instead increase their relativistic mass. this would have a bending effect, but since we assumed perfect rigidity that would not be possible. so no chance making an ftl drive out of unrealistic lumber (i cringe to think of how long it would take to mill such a cosmic tree). 

Edited September 3, 2020 by Nuke

[K^2]

57 minutes ago, JoeSchmuckatelli said:

Wild Donkeyed Guess - but are you referring to entanglement or some other thing of which I'm blithely unaware?

No. Entanglement doesn't affect communication speed. It can be used to push more data through a channel that exists, but can't be used to establish a different line of communication. See No-Communication Theorem and Quantum Teleportation for a bit more detail.

The actual problem is that light speed is a local limit due to space-time curvature being a thing. Curvature is all about distances between two points, and that can be path-dependent. Gravitational lensing is a good example. Light travels along the optimal path between two points. So if you see an object, a length of the path that light took is a good definition for the distance between objects. So what happens if light from a distant qusar passes by a galaxy with a black hole in its center and you end up with something like Einstein Cross? Now you have five different images of that quasar. Five different paths light was able to take to get to you. Five different lengths all being candidates for distance. Some of these are going to be shorter than others. Even if you chose the smallest value as "distance", the galaxy in between moving across can shift that ratio. You might measure the distance, send a message, and by the time the message makes it to the lensing galaxy, it would have moved out of alignment enough to allow for an even shorter distance, resulting in the message getting to you faster. Is that FTL? It's a stretch, but it gets you what you want, that is message getting faster than you expected based on measured distance and speed of light.

If we are talking pure theory, there is no real limit. You can fold the space-time in such a way that any two points end up arbitrarily close to each other to send the message, then unfold the space-time again. In practice, of course, we have no such capability and based on our current understanding of physics, might never have that capability. But natural events that make space-time behave in very strange ways do exist out there, so a blanket statement about speed of light limit on communication is technically false.

[SOXBLOX]

7 minutes ago, K^2 said:

If we are talking pure theory, there is no real limit. You can fold the space-time in such a way that any two points end up arbitrarily close to each other to send the message, then unfold the space-time again. In practice, of course, we have no such capability and based on our current understanding of physics, might never have that capability. But natural events that make space-time behave in very strange ways do exist out there, so a blanket statement about speed of light limit on communication is technically false.

Oh, no... Don't feed the sci-fi fanboys...

[JoeSchmuckatelli]

39 minutes ago, K^2 said:

No. Entanglement doesn't affect communication speed. It can be used to push more data through a channel that exists, but can't be used to establish a different line of communication. See No-Communication Theorem and Quantum Teleportation for a bit more detail.

The actual problem is that light speed is a local limit due to space-time curvature being a thing. Curvature is all about distances between two points, and that can be path-dependent. Gravitational lensing is a good example. Light travels along the optimal path between two points. So if you see an object, a length of the path that light took is a good definition for the distance between objects. So what happens if light from a distant qusar passes by a galaxy with a black hole in its center and you end up with something like Einstein Cross? Now you have five different images of that quasar. Five different paths light was able to take to get to you. Five different lengths all being candidates for distance. Some of these are going to be shorter than others. Even if you chose the smallest value as "distance", the galaxy in between moving across can shift that ratio. You might measure the distance, send a message, and by the time the message makes it to the lensing galaxy, it would have moved out of alignment enough to allow for an even shorter distance, resulting in the message getting to you faster. Is that FTL? It's a stretch, but it gets you what you want, that is message getting faster than you expected based on measured distance and speed of light.

If we are talking pure theory, there is no real limit. You can fold the space-time in such a way that any two points end up arbitrarily close to each other to send the message, then unfold the space-time again. In practice, of course, we have no such capability and based on our current understanding of physics, might never have that capability. But natural events that make space-time behave in very strange ways do exist out there, so a blanket statement about speed of light limit on communication is technically false.

Thanks for the explication!

 

[K^2]

4 hours ago, SOXBLOX said:

Oh, no... Don't feed the sci-fi fanboys...

I did add the "in practice" clause...

[SOXBLOX]

3 minutes ago, K^2 said:

I did add the "in practice" clause...

Do they ever read that?

[Codraroll]

10 hours ago, Bill Phil said:

Information can't travel faster than light.

Interestingly, monarchy can, but physics are satisfied because the message of monarchy can't reach the monarch faster than the speed of light.

If the Queen of England went to Mars and died on the front lines fighting sandworms, the message of her death would take approximately 15 minutes to reach her heir apparent back on Earth. However, as there must always be a monarch, monarchy is transferred instantly when one monarch dies. In other words, by the time the heir apparent received the news of the Queen's passing, they would have been king/queen themselves for a full 15 minutes already. This could raise some really interesting legal implications. For instance, if the heir apparent were to make some statements or orders while the message was en route, would it count as an exercise of royal powers?

In other words, if you want to instantly affect the other end of a light-year long bar, you would have to declare "the unbroken end of the bar that's closest to me is the most important end of the bar", then break off a piece of the bar at your end.

Edited September 3, 2020 by Codraroll

[K^2]

7 hours ago, Codraroll said:

If the Queen of England went to Mars and died on the front lines fighting sandworms, the message of her death would take approximately 15 minutes to reach her heir apparent back on Earth. However, as there must always be a monarch, monarchy is transferred instantly when one monarch dies.

Ah, but there is immediately a problem with that. Two events that are simultaneous in one coordinate system aren't in another. Just as heir apparent on Earth becomes monarch the instance Queen dies on Mars, the UK Embassy on the Moon swings around its orbit and happens to be moving away from Mars at nearly 1km/s. From their perspective, heir apparent became monarch about 5 nanoseconds before the Queen died. That's not a lot of time, but it's still high treason. They declare that a traitor cannot possibly have become a monarch legally, and call for different successor. Australia, moving in opposite direction to UK on Earth's surface, sees a smaller time difference, but agrees on the premise, setting up an international incident, with UK and Australia having different monarchs as head of government while still claiming to be under the same monarchy.

I think, to fix this, you can work with "There must always be a monarch," but then you have to concede that exact identity of monarch is frame-dependent. Which can add to confusion about orders given, as now not only is it hard to measure whether they were given before or after, but it might actually be different in fact depending on how rapidly and in what direction the person happens to be moving when receiving these orders. Fortunately, I don't see this making a practical difference until we start building much faster ships.

[YNM]

Spoiler

9 hours ago, K^2 said:

17 hours ago, Codraroll said:

Interestingly, monarchy can, but physics are satisfied because the message of monarchy can't reach the monarch faster than the speed of light.

I think, to fix this, you can work with "There must always be a monarch," but then you have to concede that exact identity of monarch is frame-dependent.

I think I have a better answer :

The head of state is simply the Crown. As in, the position. The particular monarch (person) is simply in whom the powers of the Crown are being vested in. In the olden days (and continuing to this day), the Crown can appoint people to represent their powers in a particular jurisdiction. This position is often known as the Governor-General.

As a result, there might be even more than one person who can exercise the power of the Crown already. The particular monarch does not affect anything at all, as I'd believe a British colony on the Moon or Mars would have their respective Governor-General.

This is similar to the Holy See for Papalcy, I believe, which remains the sole place where the powers really are, and are simply being vested in the Pope. The position can go vacant for months to years just fine.

 

[magnemoe]

On 9/3/2020 at 11:15 AM, Codraroll said:

Interestingly, monarchy can, but physics are satisfied because the message of monarchy can't reach the monarch faster than the speed of light.

If the Queen of England went to Mars and died on the front lines fighting sandworms, the message of her death would take approximately 15 minutes to reach her heir apparent back on Earth. However, as there must always be a monarch, monarchy is transferred instantly when one monarch dies. In other words, by the time the heir apparent received the news of the Queen's passing, they would have been king/queen themselves for a full 15 minutes already. This could raise some really interesting legal implications. For instance, if the heir apparent were to make some statements or orders while the message was en route, would it count as an exercise of royal powers?

In other words, if you want to instantly affect the other end of a light-year long bar, you would have to declare "the unbroken end of the bar that's closest to me is the most important end of the bar", then break off a piece of the bar at your end.

Yes, but outside of the reference frame issue K^2 talked about this is no different from 200 years ago and news used days to weeks to travel even months to far ways places.
Can imagine it would be issues for stuff like ending an war. 
Imagine an English warship on blockade duty  outside an French colony. England and France sign an peace agreement. 
The warship is obliviously not an pirate now as the captain don't know about the peace agreement and the ship would continue to operate until it returned to an port at an English colony who has received news that the war is over. 
And yes back in the age of sail this sort of duty could be very lucrative so they would likely want to continue as long as they could. 

[kerbiloid]

On 9/3/2020 at 12:15 PM, Codraroll said:

In other words, if you want to instantly affect the other end of a light-year long bar, you would have to declare "the unbroken end of the bar that's closest to me is the most important end of the bar", then break off a piece of the bar at your end.

Monarch of Schroedinger. Maybe rules, maybe no.

[JoeSchmuckatelli]

... And these last few posts are why I read these forums!