[Luis Dias]

I think that's not exactly it, I've seen the actual physics explanation some time ago and it did hurt my brain a little. The reason I say it's probably not that is because that seems easily solvable. If you have for instance 10 or 20 pairs of entangled electrons or wtv you can have your confirmation through sheer numbers / statistics by correlation. Error prone, but still possible (I think!).

Thing is, the data is inherently incomplete until you get the other piece of the measurement. Which seems weird and counter-intuitive, for it hints that a transmission of some kind happened, but not at all at the same time. That a piece of information was sent but not exactly at the same time. And that's exactly it, that's Quantum Mechanics for ya!

It all seems to behave weirdly and violating GR everywhere, but when you actually do the maths and try to account for everything, we see that it does not in fact, that the "information" sent FTL was not sufficient to even be labeled as "information".

[Mongoose]

It's easy to directly convert matter to energy; campfires.

Noooooo.  A campfire does NOT transfer any matter directly to energy.  The light and heat produced by a fire are a result of energy transferring forms; a fire is an exothermic reaction in which the potential energy in the chemical bonds of the fuel source (like wood, for instance) is converted into infrared and visible light.  If you set up a controlled closed environment in which to burn something, which several notable chemists did starting in the 1700s, you'd find that the total mass of the reactants was equal to that of the products; it turns out that conservation of mass is kind of a big deal.  Technically you'd see a veeeeery small reduction in mass due to the release of electromagnetic energy, but it's miniscule enough that you'd need very precise instruments to observe it.  You'd need to look at nuclear reactions to see the conversion of matter to energy in a truly-noticeable sense in relation to the reactant masses involved.  It's not really "easy" in the sense that you can do it with stuff you find around your house, though it is something that humanity as a whole does routinely every day.

[AdmiralRalwood]

You can well create (theoretically) a drive that shortens the distance between A and B. What you (and many others!) are missing is that the process of "shortening up" the distance between A and B is through gravitational waves... which travel at light speed! See the problem? You can't get around this.

I can't find any reference to gravitational waves on the Wikipedia article for the Alcubierre Drive...

[S-99]

Noooooo.  A campfire does NOT transfer any matter directly to energy.  The light and heat produced by a fire are a result of energy transferring forms; a fire is an exothermic reaction in which the potential energy in the chemical bonds of the fuel source (like wood, for instance) is converted into infrared and visible light.  If you set up a controlled closed environment in which to burn something, which several notable chemists did starting in the 1700s, you'd find that the total mass of the reactants was equal to that of the products; it turns out that conservation of mass is kind of a big deal.  Technically you'd see a veeeeery small reduction in mass due to the release of electromagnetic energy, but it's miniscule enough that you'd need very precise instruments to observe it.  You'd need to look at nuclear reactions to see the conversion of matter to energy in a truly-noticeable sense in relation to the reactant masses involved.  It's not really "easy" in the sense that you can do it with stuff you find around your house, though it is something that humanity as a whole does routinely every day.

Conservation of mass is a big thing indeed. Most of the output from a camp fire is smoke, other gasses, carbon.. It might a crude form of converting matter to energy. However, you're still at least getting infrared and visible light output from wood. I know what you mean though. That lighting a fire starts a tiny process of matter to energy conversion but that that what is happening in the least since most of the output from a fire is matter; that a fire is mostly conversion of matter to other forms of matter.

Nukes would be a better example?

[IronBeer]

Noooooo.  A campfire does NOT transfer any matter directly to energy.  The light and heat produced by a fire are a result of energy transferring forms; a fire is an exothermic reaction in which the potential energy in the chemical bonds of the fuel source (like wood, for instance) is converted into infrared and visible light.  If you set up a controlled closed environment in which to burn something, which several notable chemists did starting in the 1700s, you'd find that the total mass of the reactants was equal to that of the products; it turns out that conservation of mass is kind of a big deal.  Technically you'd see a veeeeery small reduction in mass due to the release of electromagnetic energy, but it's miniscule enough that you'd need very precise instruments to observe it.  You'd need to look at nuclear reactions to see the conversion of matter to energy in a truly-noticeable sense in relation to the reactant masses involved.  It's not really "easy" in the sense that you can do it with stuff you find around your house, though it is something that humanity as a whole does routinely every day.

Conservation of mass is a big thing indeed. Most of the output from a camp fire is smoke, other gasses, carbon.. It might a crude form of converting matter to energy. However, you're still at least getting infrared and visible light output from wood. I know what you mean though. That lighting a fire starts a tiny process of matter to energy conversion but that that what is happening in the least since most of the output from a fire is matter; that a fire is mostly conversion of matter to other forms of matter.

Nukes would be a better example?

Aaaaaaack nooooooo. A fire is not mass->energy conversion. Period. You're taking a material at a stable high-energy state, and performing a chemical reaction to result in low-energy but high-entropy byproducts. Conservation of mass isn't just a "big thing", it's the ONLY thing.

Nuclear reactions, and practically speaking nuclear reactions ONLY, involve mass->energy conversion.

(Ok, fine, obnoxious pendant corner: photons do have mass, so any EM energy emitted by a burning campfire would "carry away" an amount of mass commensurate with the energy radiated. However, this amount of energy is unspeakably miniscule compared to the total binding energy of a campfire's fuel, so for any real-world purpose is utterly negligible. To put into perspective just how much energy is tied up in the very being of matter, complete conversion of a single gram of matter to energy would release about as much energy as a super-high-yield thermonuclear weapon. Now compare that against a couple kilos of firewood. Yeah, there's a reason nobody counts mass loss from combustive EM emissions.)

[Herra Tohtori]

You can actually precisely calculate the mass -> energy transformation in a chemical reaction such as combustion.

If you have a molecule such as C₂H₅OH, and a stoichiometric amount of O₂ (I'm too lazy to actually calculate the ideal ratio), turns out these molecules are slightly more massive than the chemicals resulting from them reacting - CO₂ and H₂O.

The energy of the chemical bonds counts as mass. Ethyl alcohol and oxygen molecule are in a higher energy state than the reaction results (carbon dioxide and water). So when you introduce enough energy into a system of ethanol and oxygen to go over the disassociation energy barrier, to split these molecules into individual atoms, the soup of atoms ends up reconfiguring it at the "easiest", aka. lowest energy configuration. The energy difference (or enthalpy) is typically transitioned to relative energy forms - kinetic energy, rotational energy, and electromagnetic radiation.

The chemical energy in the bonds does have an effect on a molecule's mass. However, you are right in that the mass difference in chemical reactions is so insignificantly small that generally it can be said that conservation of mass applies in chemical reactions. That is because the ratio between energy and mass is c², which is a large number, and chemical reactions typically don't produce very much energy - you need quite a lot of reactants to produce meaningful amount of energy.

In nuclear reactions the mass difference is actually measurable and that's why nuclear reactions produce so much energy from seemingly small amount of reactants.


In short: Chemical energy is differences in energy configurations of electrons. Nuclear energy is differences in energy configurations of protons and neutrons.

Since electron configurations are purely a result of electromagnetic interactions (in the quantum mechanical sense) and nuclear configurations are a result of mostly strong nuclear interaction*, it makes perfect sense that there is a lot more energy involved in nuclear configurations, compared to electron configurations. Strong nuclear interaction is just so much stronger than electromagnetic interaction.

*Nuclear configurations can also be affected by weak nuclear interaction, which is responsible for such things as electron capture where proton and electron interact and the proton changes into a neutron, and if I recall right the reaction also produces an electron neutrino. But in nuclear scale, the strong nuclear force vastly overpowers electromagnetic force which is, happily, the reason why matter stays intact. It's also the main reason why physically very large nuclei form instabilities in heavy elements, and become radioactive - the nuclear binding energy is reducing as radius of nucleus increases, while the electromagnetic repulsive energy increases as the amount of positive charges increases...

But, for practical purposes, if Alcubierre drive allows traveling from A to B faster than distance between A to B seems to be I would call it FTL travel and be done with it.

You didn't understand the criticism against the AD.

I did, you just didn't understand why your critique was invalid.

You can well create (theoretically) a drive that shortens the distance between A and B. What you (and many others!) are missing is that the process of "shortening up" the distance between A and B is through gravitational waves... which travel at light speed! See the problem? You can't get around this.

Your critique would be right if Alcubierre Drive were a "wave rider" of sorts.

Instead, it is based on creating new space behind the ship while reducing the amount of space ahead of it. Expansion and contraction of space are not in any way limited by the speed of light.

In short, Alcubierre drive would actually create an event horizon behind it since space there would be expanding faster than light can travel through it. On the front end, though, there's an opposite problem since the drive would essentially contract the space ahead - with all the photons included in that space that happen to be in it, and that would cause insane photon density.

A more valid critique would be to ask how the space-time expansion is contained so that it only translates to ship apparently moving and not, say, the universe suddenly splitting in half.

Perhaps something like creating "lanes" would eventually be possible. Really far fetched and not at all what is being discussed when speaking about ADs, since they depend on the idea of not only shortening AB but also lengthening AB in the "back" of the drive. Since this process cannot happen faster than the waves making the lane, you are still travelling slower than light.

This is basically the "stargate" method - creating a wormhole between two devices, then moving one device somewhere else while keeping the wormhole connected. Rate of creating these traveling methods would indeed be limited by how fast the other end can be transported, but once the wormhole is established, traveling through it does offer a true "bypass lane" over the limitations of space-time continuum - in effect, it creates a space-time connection between two positions that is separate from the traveling distance. This is completely free of any paradoxes, too.

Yeah, well, the problem with uncharted territory is you don't know what's behind the next hill until you get an overhead satellite pass to give you a picture.

But we do have a lot of pictures. They are all quite pessimistic in this notion. You are of course free to dream, but never should be under the illusion that current physics are giving you hints for your optimisms, for they are clearly not.

We don't have pictures, we have "artist's impressions", which is a fancy way of saying we have theories and visualizations based on those theories. These should be kept separate from actual empirical data.

[Killer Whale]

But, for practical purposes, if Alcubierre drive allows traveling from A to B faster than distance between A to B seems to be I would call it FTL travel and be done with it.

Distance between A and B: Looks about 100 ly away. If I go at 0.9c it'll take about 111 years.
Accelerate to 0.9c: Oh, it only looks 44 ly now, it should only take 48 years.
Yay, I went 100 ly in 48 years, I FTL

[Herra Tohtori]

But, for practical purposes, if Alcubierre drive allows traveling from A to B faster than distance between A to B seems to be I would call it FTL travel and be done with it.

Distance between A and B: Looks about 100 ly away. If I go at 0.9c it'll take about 111 years.
Accelerate to 0.9c: Oh, it only looks 44 ly now, it should only take 48 years.
Yay, I went 100 ly in 48 years, I FTL

It needs to apply in the original reference frame, though.

I am fully aware that time dilation will make the travel time shorter the closer you get to light speed (or, alternative explanation - the travel distance experiences Lorentz contraction and becomes shorter) but it will still take too much time to really explore the galaxy and every long distance travel will be strictly one-way - which is no way for scientific exploration to operate. It would work for colonization missions, but even if you push the speed closer to c and thus reduce travel time for the ship itself - you encounter situations where thousands of years will progress on Earth with months or years for the ships occupants.

And it's even worse if you don't send people, because then the only advantage is that your unmanned research probe won't age, but it will still take hundreds or thousands of years until it actually seems to get to its destination... and in fact it'll look like twice that time because the further it gets, the longer it takes for signals to get to Earth. We'll be able to track its progress in "real-time" but there will be an ever-increasing delay between the time when the probe does something and the time we receive the image it took or whatever. And it would of course need to be autonomous because trying to control robots on MARS is a pain in the neck, never mind several years of control delays.

[Luis Dias]

So I just found out I never replied to this and so here I am .

But, for practical purposes, if Alcubierre drive allows traveling from A to B faster than distance between A to B seems to be I would call it FTL travel and be done with it.

You didn't understand the criticism against the AD.

I did, you just didn't understand why your critique was invalid.

You can well create (theoretically) a drive that shortens the distance between A and B. What you (and many others!) are missing is that the process of "shortening up" the distance between A and B is through gravitational waves... which travel at light speed! See the problem? You can't get around this.

Your critique would be right if Alcubierre Drive were a "wave rider" of sorts.

Instead, it is based on creating new space behind the ship while reducing the amount of space ahead of it. Expansion and contraction of space are not in any way limited by the speed of light.

In short, Alcubierre drive would actually create an event horizon behind it since space there would be expanding faster than light can travel through it. On the front end, though, there's an opposite problem since the drive would essentially contract the space ahead - with all the photons included in that space that happen to be in it, and that would cause insane photon density.

A more valid critique would be to ask how the space-time expansion is contained so that it only translates to ship apparently moving and not, say, the universe suddenly splitting in half.

You see, you say you understood the critique and then bluster right through it. Let's try this again, I *get* the mechanism. I get the "expansion or contraction" of space thing. What you are missing is that the space itself has to acquire the information that is being compacted. The only known mechanism in physics on how this happens is through gravitational waves. You have to communicate to space itself that you want it to contract itself and in what manner. This is what you cannot communicate FTL.

And, anyway, the AD is really simple to defuse as a theoretical concept by fiat. If you picture a "surrounding sphere" of a million kms that encompasses the ship, the drive, the space being contracted, etc., you can judge it theoretically as a kind of a particle in the universe and analyse it accordingly. This "particle" cannot travel faster than light, period.

I have watched silly talks about the AD, supposedly by smart people, trying to get around the time travel paradoxes that it would imply, and their solution was something of the sort of a traffic legalization, forbidding certain closed paths and so on. It's remarkably silly, as if they were trying to prevent the universe from figuring out that they were cheating its laws.

This is basically the "stargate" method - creating a wormhole between two devices, then moving one device somewhere else while keeping the wormhole connected. Rate of creating these traveling methods would indeed be limited by how fast the other end can be transported, but once the wormhole is established, traveling through it does offer a true "bypass lane" over the limitations of space-time continuum - in effect, it creates a space-time connection between two positions that is separate from the traveling distance. This is completely free of any paradoxes, too.

Yes, this would be apparently free of paradoxes, although the fact that one mouth of the wormhole is accelerated will bring about severe problems and bring back the time paradox issues to light. Some literature exists over this, and it seems to point out that differently accelerated mouths will obviously create different time relations, but because this is incompatible with the requirement that both mouths must be perfectly synchronized, the hole just collapses.

[S-99]

Aaaaaaack nooooooo. A fire is not mass->energy conversion. Period. You're taking a material at a stable high-energy state, and performing a chemical reaction to result in low-energy but high-entropy byproducts. Conservation of mass isn't just a "big thing", it's the ONLY thing.

Nuclear reactions, and practically speaking nuclear reactions ONLY, involve mass->energy conversion.

(Ok, fine, obnoxious pendant corner: photons do have mass, so any EM energy emitted by a burning campfire would "carry away" an amount of mass commensurate with the energy radiated. However, this amount of energy is unspeakably miniscule compared to the total binding energy of a campfire's fuel, so for any real-world purpose is utterly negligible. To put into perspective just how much energy is tied up in the very being of matter, complete conversion of a single gram of matter to energy would release about as much energy as a super-high-yield thermonuclear weapon. Now compare that against a couple kilos of firewood. Yeah, there's a reason nobody counts mass loss from combustive EM emissions.)

It's such a horrible example i see why it's not counted as a conversion now. Just because of it's extreme minisculity. And candidates for real considerration are few.

[Herra Tohtori]

You see, you say you understood the critique and then bluster right through it. Let's try this again, I *get* the mechanism. I get the "expansion or contraction" of space thing. What you are missing is that the space itself has to acquire the information that is being compacted. The only known mechanism in physics on how this happens is through gravitational waves. You have to communicate to space itself that you want it to contract itself and in what manner. This is what you cannot communicate FTL.

You only need to expand or contract the space that is right next to the ship. There's no need to affect anything faster than light.

Besides, I wouldn't go so far as to say that gravitational waves are the only way to change the space-time curvature. That's a fallacy because gravitational waves are propagating variations of space-time curvature - they don't explain what makes the space curved. There is a thing we only have a name for that apparently has the effect of negative pressure (or anti-gravity) on the entire universe. We don't understand why the universe expanded so rapidly during the inflation phase of the big bang. We don't even understand why mass curves space-time - we just have witnessed that it does, and we have a pretty good theoretical model to analyze mass-space-time interactions - it's called General Relativity.

And, anyway, the AD is really simple to defuse as a theoretical concept by fiat. If you picture a "surrounding sphere" of a million kms that encompasses the ship, the drive, the space being contracted, etc., you can judge it theoretically as a kind of a particle in the universe and analyse it accordingly. This "particle" cannot travel faster than light, period.

Your argument is simple to defuse by empirical observation that there are a hell of a lot of particles in the universe that are moving away from us faster than light. You only need to look deep enough, and you see an event horizon which hides the rest of the universe racing away from us.

And, like I just said, that expansion is acceleration due to... something that we just have a name for, and some sort of rudimentary observational formula for how it accelerates the expansion of our universe.

I have watched silly talks about the AD, supposedly by smart people, trying to get around the time travel paradoxes that it would imply, and their solution was something of the sort of a traffic legalization, forbidding certain closed paths and so on. It's remarkably silly, as if they were trying to prevent the universe from figuring out that they were cheating its laws.

They probably seem silly to you because you lack the theoretical understanding to comprehend what they're talking about. I have seem the same thing with people who are opposed to evolution, natural selection, WTC collapse without being "inside job", or indeed the Big Bang itself. These people all had the common denominator of criticizing things they didn't really understand.

And I'll openly admit that I don't have the understanding to critique something like Miguel Alcubierre's (speculative) solution to Einstein's field equations from the general relativity.

However, the people who come up with this stuff have made it their life's work to do it and experiment with it and figure out what's possible and what's currently not. As far as I understand, no one has proven Alcubierre's solution mathematically incorrect; having been published in a peer-reviewed magazine and survived for several years, someone probably would have caught a mathematical error by now.

So it appears to remain a viable solution that is compatible with general relativity - which is the aforementioned model that is currently the best available for predicting mass-spacetime interactions.


Whether or not it is actually possible, or if general relativity itself is wrong in this regard - that remains to be seen, but it needs to be tested because not even all the king's men together with all the king's horses and a court magician with best armchair physics in the kingdom can't prove OR disprove it.

They need to either have someone come up with a "look, you put a + here instead of -" or to figure out an experiment that can conclusively disprove the Alcubierre solution.

This is basically the "stargate" method - creating a wormhole between two devices, then moving one device somewhere else while keeping the wormhole connected. Rate of creating these traveling methods would indeed be limited by how fast the other end can be transported, but once the wormhole is established, traveling through it does offer a true "bypass lane" over the limitations of space-time continuum - in effect, it creates a space-time connection between two positions that is separate from the traveling distance. This is completely free of any paradoxes, too.

Yes, this would be apparently free of paradoxes, although the fact that one mouth of the wormhole is accelerated will bring about severe problems and bring back the time paradox issues to light. Some literature exists over this, and it seems to point out that differently accelerated mouths will obviously create different time relations, but because this is incompatible with the requirement that both mouths must be perfectly synchronized, the hole just collapses.

Why would the hole just collapse? There's no requirements that I know of that require two points in space-time to be synchronized to each other (in fact, two points in space-time rarely are synchronized in any way anyway).

Wormholes have other issues that would be much more pressing, like the fact that you just made a black hole appear right in your vicinity and you have to deal with the insane tidal forces and make the wormhole itself stable (which, by the way, requires the same exotic matter that is supposedly required to make Alcubierre Drive work!) and possible to go through without becoming tissue spaghetti heated to luminous plasma on the way.

Do feel free to come up with more ideas to disprove the impossibility of this or that scientific hypothesis, but please keep in mind that Alcubierre drive is a theoretically valid solution derived from General Relativity, and you're basically trying to disprove it by basic arguments from General Relativity.

I can't help but think that these clever people would've noticed this by themselves if it really were as simple to disprove as what you're suggesting.