N_las

Relativity isn't just signal delay. There is a lot more to it. And no, event B doesn't happen after event A in ANY case. Just look at this: http://en.wikipedia.org/wiki/Relativity_of_simultaneity It doesn't matter which two events A and B you choose in the universe, there will be always frames of reference were the order is A-B and others were the order is B-A. This is not due to signal delays.

Are you for real? Of course we can use 2D diagramms for space-time, as long as only one spacial dimension is relevant. I am not ridiculing myself, I understand "what Einstein had in mind" to a reasonable degree. If you think I "clearly do not", then point to a single error I made. I made "so many logical errors"... I don't see any. The only error I made with the bomb example is the direction the hostile bomb had to travel. It renders the story around the example meaningless, but it is a irrelevant detail for the idea behind the process. I corrected that in my diagramms. Yes, i am not trying to argue that the paradox would be reason to belive that FTL must be impossible because it would "break" physics. I just want for Gpysic to finally understand that time travel and FTL has to go hand in hand.

That isn't a violation of local causality. Please learn the meaning of words before you use them. Imagine Causality to be a law like: "All people are only allowed to travel from west to east, not the other way around." Local causality would be only violated if you find a place on earth were somewere is traveling against the stream. But if someone travels always to the east, and he finds himself at a city WEST of his starting point (because the earth may be round), then only global causality is broken. Local causality still isn't violated, because he never took a step in westward direction. IF you look at my examples (http://imgur.com/a/9x5pV), you will see that you are basically right. If the people that jumped after the rocket in their alcubierre-ship would simply jump back, they wouldn't be in their past. It would just be like you claimed. But thats the reason my example contains the rocket with a second alcubierre-drive. Because the earth is travelling away from the rocket at 0.5c, when they use the second alcubierre-drive, they will land in earths past. Please find an actual flaw in the explanations given in the diagramms. They clearly demonstrate that time travel with alcubierre-drives is possible. Cognitive bias is strong in this one^^ Just like the alcubierre-drive, Einstein-Rosen bridges can also be used to travel through time. The mechanism described on wikipedia may be differnent than my example, but that doesn't matter. I am not ignoring that "Einstein himself came up with solutions where there are ways to overcome the limitations of relativity". I am simply pointing out, that this solution will enable time travel. And everyone who has a basic understanding of physics can see that. You are still using the argument.... Please, Please, PLEASE look at my diagramms: (http://imgur.com/a/9x5pV) look at them hard and try to understand them. JUST LOOK AT THEM. Now tell me: Where does the "movement" or "not movement" of the ship during its FTL "travel" matter? Please point it out! WHERE, WHERE? Nowhere!!! The argument of "no actual movement" is just weak and shows that you havn't understood anything. The only FTL related thing that matters in my example are the starting points and the end points of FTL "jumps".

That is just relativity. As long as one doesn't understand that, one is still thinking like Galileo Galilei about space and time (two seperate entities). Here is an exhaustive explanation: http://en.wikipedia.org/wiki/Relativity_of_simultaneity

That post gave me cancer.

Thats not what it said. The observers can disagree about the order of events (as long as the events happen at different places). please look at the diagramms I made: http://imgur.com/a/9x5pV There, I explained it clear and without ambiguity.

You have to give a definition of what you mean by "possible", "impossible", "something" and "everything". Human language is incredibly imprecise. Many words have many different meanings based on context. It is not useful to use imprecise words in a logical argument. Feathers are light. light is not dark -> There are no dark feathers.

I think the black hole has an entropy only dependent on its surface area. If stuff falls into it, the entropy of this stuff isn't lost to the unverse, but in has increased the entropy of the black hole. By hawking radiation, the entropy can "leave" the black hole again.

The effect has nothing to do with any singal delays due to the speed of light. I made a detailed explanation with diagramms. It isn't the previously described bomb scenario, but a different one. I hope everyone can understand it. The explanation is in the image descriptions: http://imgur.com/a/9x5pV I think the previously described bomb scenario doesn't work exactly as described earlier, because the hostile bomb actually has to travel away from earth, not towards it. But the principle behind the idea is still correct (just the story about an insterstellar war has to be changed to something different). If anyone has more questions about the diagramms, please ask. I want this out of the world. This is the third or fourth time this exact topic has come up, and there are always people who are immune to understanding. I want to improve this example, the diagramms and the explanation up until the point were it is optimal. Then in the future hundrets of discussion and questions, we simply can link to this post.

This diagram really does explains it well: http://www.theculture.org/rich/sharpblue/images/causalityviolation.png There are four people involved: Alice, Bob, Dave and Carol The white lines describe the frame of reference for Alice and Bob (stationary to each other). The blue lines describe the frame of reference for Dave and Carol (statinary to each other, but no to Alice and Bob) Ignore the red lines for the moment. There are three events depictet in the diagramm. Event P, event Q and event R. The yellow cones are the light cones of event P and event Q. A diagonal of 45° is a light beam that travels with c. From Alices and Bobs point of view, event P and event Q happens at the same time and event R happens before them. From Dave and Carols point of view, event R and event Q happens at the same time, and event P happens after them. This has nothing to do with any FTL travel effects, it is just basic relativity and stems from the fact that Dave and Carol are moving in respect to Alice and Bob. This wiki-page explains it in more detail: http://en.wikipedia.org/wiki/Relativity_of_simultaneity Normally, event P couldn't influence event Q in any way, because Q is outside of Ps light cone. And event Q couldn't influence event P or event R. Only event R can influence event P, because P is in Rs light cone. The following explanation assumes instant communication, but any communication faster then light will allow for a similar situation: At event P Alice makes a instant transmission to Bob (event Q). Carol can be influenced by event Q. Carol can send an instant transmission to Dave at event R. Event R can influence event P. Notice, that from Alice and Bobs reference frame (the white lines that are drawn at right angles), the commnucation between Q and R goes backwarts in time. From Dave and Carols reference frame (the blue angled lines) the communication between event P and event Q goes backwarts in time. Furthermore, one could draw the same situation with the blue lines for Dave and Carols reference frame beeing at right angles, and the white lines for Alice and Bobs frame beeing angled. Such a diagramm would be just as correct. Notice, that it doesn't matter how the communication between P and Q or Q and R takes place. The claim from gpisic and cicatrix, that the effect would come from the actual "movement" of the infromation carrier is simply false. The only relevant movement is the one of Dave and Carol at slower than light speeds. The information can be magically transfered, teleported, Uri-Gellered or transfered via Warp drives. As long as Event P can somehow influence any event outside of its future light cone, it will allow for this sort of time travel.

Disapointing that the experiment hat increased twisting. We have suggested an explanation for this back somewere in this thread. I will try to find it. I don't know if this is the right explanation, but it clearly is no mysterious behaviour. EDIT: Here is a possible explanation from the past of this topic:

No, you havent understood the explanations then. It doesn't have to do with the "movements" during the FTL travel. The only relevant "movement" is the hostile bombs movement at nearly the speed of light, which doesn't need any FTL technology. The Warp drive is only used to bring some information from event A to event B (while B is outside of As light cone). It doesn't matter how the information got there, it doesn't matter it the information carrier moved through space or simply teleported by magic. Please read the infamous "FTL communication" thread: http://forum.kerbalspaceprogram.com/threads/93377-FTL-communication It gets interesting at post #96 (on page 10)

I already explained it several times: There is another explanation on wikipedia: http://en.wikipedia.org/wiki/Time_travel#Via_faster-than-light_.28FTL.29_travel And here is another explanation: http://www.theculture.org/rich/sharpblue/archives/000089.html The hostile bomb can execute an evasive maneuver before the counter-bomb is started. That is, because from the hostile bombs point of view (remember, it travels at 99.999% the speed of light) the order of events is reversed: FIRST: The counter-bomb reaches the hostile bomb and executes the countermeasure. SECOND: The counter-bomb is started at earth. This is only possible because the hostile bomb uses a warp drive. see the above Explanations.

When from the hostile bombs inertial reference frame event B can happen before event A, the hostile bomb can react to B by engaging its own warp-drive and reach earth before A happens. So the earth can be destroyed by the hostile bomb BEFORE we sent the counter-measure. If we don't send the counter measure, then the earth is destroyed by 2080. But because we send the countermeasure in 2040, the earth is destroyed in 2039. But if the earth is destroyed in 2039, we couldn't have sent the countermeasure in 2040. But if we couldn't have sent the counter-bomb, the earth should have been destroyed in 2080. But then we CAN launch the countermeasure in 2040 .... The reason why we CAN'T launch the countermeasure is that we WILL sent the countermeasure. Global causality is broken.

We don't have to spot the bomb ourselfs. It doesn't matter for this scenario. Maybe the hostile civilization has contactes us thousands of years ago, explaining that it will send this kind of bomb in the future. If the enemy planet is thousands of light years from earth then yes: thousands of years will pass on the enemy planet before the bomb reaches earth. Doesn't have anything directly to do with time dilation. But it doesn't matter. Maybe they sent it thousands of years ago. We don't have to discuss the reason behind alien military strategies. It doesn't matter. By "travel", i don't meen that the ship acutally has this velocity. "travel" simply means that I start at a start position and end up at a destination. It doesn't matter if i am actually moving, i can still travel FTL. If I appear at the destination faster than a light beam would reach the destination (that would have been send out at the start position instead of me), then the phrase "I traveld FTL" is justified, even if I didn't move. We don't need a scout for this scenario. And why are you talking about the counter-bomb to "arrive earlier than #1"? What does the start of the hostile bomb has to do with anything? If event A is the start of the counter bomb, and event B is the meeting of the bombs, from earths inertal reference frame, then event B happens after event A. But because the counter bomb reached event B earlier than a light beam from event A would reach it (a light beam could not travel from event A to event , event B happens outside of the light cone of event A. Because Event B is outside of event As light cone, from the hostile bombs inertial reference frame (it travels near light speed) event B can happen before event A. If the hostile bomb would travel at lower than light speeds, it couldn't reach the earth before event A, but if it itself has a warp-drive, it can reach Earth before event A. The counter-bomb would try to destroy the hostile bomb. It has to have some kind of influence on the hostile bomb for that. Maybe a giant explosion just infront of the hostile bomb? Doesn't really matter for this scenario. The hostile bomb only has to survive the countermeasure, and has to notice the countermeasure. Yes, you are wrong about this. My whole bomb scenario is there to illustrate how the warp-drive can violate causality. It isn't dependent on "something actually moving faster than light". The only important movement is the hostile bombs near-light-velocity relative to earth.

It doesn't need to be directly or practical: Imagine a Bomb travelling with 99.999% light speed towards earth. It was set up by a hostile civilization. A Countermeasure-bomb is started from Earth to explode in the vicinity of the hostile bomb in the hope to destroy it. To have this counteraction take place as far from earth as possible, the Counter-Bomb is fittet with an alcubierre drive. It travels with greater than lightspeed towards the hostile bomb. Event A is the start of the counter-bomb from Earth, and event B is the meeting of the counter-bomb with the hostile bomb. You will agree, that it is possible for event B to happen before event A in the inertial reference frame of the hostile bomb. As soon as the counter-bomb reaches the vicinity of the hostile bomb, it explodes. I am not sure what should happen with the warp bubble. I assume the bomb has to exit it before or during the explosion. Now imagine the hostile bomb is also fittet with an alcubierre drive. It withstands the explosion (maybe the counter bomb exploded to far away). As some kind of counter-countermeasure, after detecting the counter-bombs explosion in its vicinity, it starts its alcubierre drive immediately. From it's point of view, event A hasn't even happen yet. If it travels at greater than light speed towards earth, it could reach it before event A. So it will destroy earth earlier BECAUSE we sent a counter-measure but BEFORE we sent the counter-measure. Clearly, the information that we sent the countermeasure travelled into the past. And cleary, global causality is violated (if earth is destroyed because we sent the counter-bomb but before we sent the counter-bomb, then we couldn't sent the counter-bomb in the first place.) I am not suggesting that any FTL drive would just be like a DeLorean in "Back to the future". But some people here on these forums don't accept that FTL travel would violate causality or they think that the alcubierre drive has some kind of "Get out of jail"-card for "FTL-travel without causality violations" because "it doesn't actually move, it's just warping the space around". But any FTL communication technology will allow for a setup that sends information back to the past of the sender. And the alcubierre drive is some kind of FTL communication technology.

While this is correct, no macroscopic body can ever by exactly symmetrical. Down to the atomic level, matter is coarse. If we talk about eternities, even that miniscule amount will stop the rotation eventually.

Then let us nitpick a bit more The rotating body will send out gravitational waves, so its rotation will stop after a long time. Therefore there wouldn't be a bulge at the equator left.

In older threads, we explained how any FTL travel will allow time travel. It has nothing to do with the movement of the ship. http://en.wikipedia.org/wiki/Time_travel#Via_faster-than-light_.28FTL.29_travel

The entropy of a system can increase while its temperature is decreasing. The universe can have a low temperature while having a high entropy. The entropy is dependent on the number of possible ways a system could be arranged. This has only an indirect connection to temperatur. It is true that a perfect crystal at zero kelvin would have zero entropy, but this is irrelevant, since nothing can ever have zero kelvin temperature. A good way to picture entropy: Imagine a set of ten normal dices. The are all showing the "1" face. They add up to a sum of 10 eyes. That is the only possible way to get 10 eyes, so the number of possible ways to arrange a "10-eye" system is very low. If you change one dice at random, it may show a "2" face. The sum of all dices is now 11 eyes. There are 10 possible ways to get 11 eyes (each dice could have the two), so the "11-eye" system has a "higher entropy" (in the sense of this games rules). If you shake your dices for quite some time, you may get a "35-eye" system. This has a giant number of possible ways to be arranged. In fact, the "35-eye" system has the maximum amount of possible arrangements, hence the highest "entropy". By slowly rolling one of your dices after the other in a random order, any system will tend to become a "35-eye" system. This is purly by chance, because there simply are more possible ways to arrange the 35-system. Getting a 10-system (or a 60-system) by chance is highly unlikely, because it has only one possible way to arrange it: only ones (or only sixes for the 60-system). I hope this explains entropy: The entropy rises simpy because of statistical reasons. The entropy is a measure of the possible ways to arrange a particular system. If there are many ways to arrange a particular system to A, and only few ways to arrange the system to B, then it is simply more likely that you will end up with A (the higher entropy state).

Something like this? http://en.wikipedia.org/wiki/Voltage_divider

@How2FoldSoup Next time you quote from a wikipedia article, read the entire section. It is the exact same explanation I have given in my previous post.

You suffer from a misunderstanding of "E=mc^2". It doesn't mean that you can interchange a certain amount of energy for a certain amount of mass, losing energy and gaining mass in the process. It DOES mean that Energy and mass is the same thing, mass is the measurment of the energy content of a system. Every system with the energy-content E has automatically the mass m, and every system with the mass m must contain the corresponding energy E. My point wasn't that ALL the mass the sun loses is photons. But those photons the sun is sending out got their mass from the fusion process. As long as you use the concept of relativistic mass, the energy that was carried away was automatically mass. I will provide a thought experiment at the end of this reply. The notion that the "long" formula containg the momentum p is the fundamental formula, and Einsteins original equations is just a special case for "p = 0" is wrong. The more fundamental formel IS "E=mc^2", and it holds perfectly true, as long as "m" is regarded as the relativistic mass. But purists (who don't like the concept of "relativistic mass") want a formula where the "m" stants for the invariant mass. This formula is the one you provide. But in any actual calculation, you can come to the same result, by regarding "m" as relativistic mass and using the simple formula "E=mc²" As the temperatur in my hand is rising, so does its energy content and its mass. Your artifical distinction between mass and energy is a thought barrier you have installed because you only regard invariant mass. See my thought experiment at the end of this reply. By transfering its Energy, the gamma photon automatically transferd the corresponding amount of mass. Your analogies are really bad. The gamma ray didn't smack the electon out of the "other particle". The electron and the positron were pair-created out of the photon. The photon lost its energy (and mass) in the process, while the positron and electron gained that energy (and mass). Consider the mass defect in nuclear fission. Your original atom has a certain nuclear binding energy. This nuclear binding energy is automatically a part of the mass of the original nucleus. If you split the nucleus, you release a bit of the binding energy. The fission products (including any stray neutrons, electrons or alpha particles) have LESS binding energy and automatically they have LESS mass. How do you explain that. If "E=mc²" does mean that you could interchange a certain amout of energy for a certain amount of mass and reverse, by REDUCING its binding energy, it should have PRODUCED Mass. In reality, "E=mc²" isn't an "exchange rate", but it means that the Energy "E" IS automatically the mass "m". The fission products have LESS binding energy, and hence LESS mass. The Energy that was binding energy is converted to kinetic energy of the fission products, and gamma photons. If you calculate the relativistic mass of the fission products and of the photons, no mass is lost. The whole process conserved energy AND mass, because both are one and the same. Let me give you a thought experiment, that is hopfully convincing: I claim that the "relativistic mass" is real. The concept of "invariant mass" may make certain calculatons easier, but it isn't more fundamental, because sometimes there is no clear distinction. Furthermore, mass and energy aren't two different things that can be exchanged, increasing one quantity while decreasing the other. This is a rampant misunderstanding. Mass and Energy are the same thing, and every amount of energy is automatically a certain amount of mass. By decreasing the energy of a system, its mass will decrease. The lost energy had to go somewhere, and the lost mass went the same way. Consider a positron-electron plasma. If the observing time is small enough, this plasma is stable (they will annihilate eventually, but only after a small amount of time). We have 1 kg of plasma. We contain it into a 0.1 kg box. From the outside, we don't know what is inside. What will we get, if we measure the invariant mass of the box? If we are at rest with the box, and we put a force of 1.1 N on the box, it will accelerate with 1 m/s². So the invariant mass seems to be about 1.1 kg (the mass of the empty box plus the mass of the plasma) If the positrons and electrons in the box annihilate over time, they "become" gamma photons. Assume the walls of the box are perfect mirrors for gamma photons, so after some time, there are only photons left in the box. But from the outside, we can't know what is happening inside the box. We only see a box. What will we get, if we measure the invariant mass of the box after the whole plasma is annihilated? The same as before! The box still seems to have the invariant mass of 1.1 kg. From the inside, we can explain that by the photon pressure on the walls. By accelerating the box, a red- and blushift of the photons will produce a different photon pressure at the opposing walls of the box, so they produce a resistance against the acceleration. But from the outside, we don't see and know that, and we don't care. From the outside, the box seems to have always just an invariant mass of 1.1 kg, it doesn't matter what happens inside. So the invariant mass of an object can be just the "relativistic mass" of the photons in disguise. You may say: The plasma lost mass, it was converted to energy, and now the photons have this energy. But what does that even mean, if the whole system behaves just as if it still had the original mass. Heck, even the gravity from the box doesn't change! And this is the case for every system. It doesn't matter how energy is converted, it always carriers its equvialent in mass. By adding 16 Wh chemical energy to my battery, it will get heavier. (The energy source, maybe a burning piece of coal, will get lighter). By compressing a mechanical spring, it gets heavier. By inducing a current into a superconducter, it gets heavier. This isn't any new physics, or just something a guy tells you on the internet. It is the fundamental meaning of the formula E=mc² http://en.wikipedia.org/wiki/Mass%E2%80%93energy_equivalence Quote: "Whenever any type of energy is removed from a system, the mass associated with the energy is also removed, and the system therefore loses mass. This mass defect in the system may be simply calculated as ÃŽâ€m = ÃŽâ€E/c2, and this was the form of the equation historically first presented by Einstein in 1905. However, use of this formula in such circumstances has led to the false idea that mass has been "converted" to energy. This may be particularly the case when the energy (and mass) removed from the system is associated with the binding energy of the system. In such cases, the binding energy is observed as a "mass defect" or deficit in the new system." The whole idea that mass and energy can be coverted into each other is just a missunderstandig, rampant because some people are to fanatic with there "invariant-mass-purism", bad high-school teachers and bad didactic choices by college professors. The question if a photon has a mass or not IS just a semantic one. Even if you claim that a photon doesn't have mass, because you are only regarding "invariant mass" as real: By putting a perfectly massless box around the photon, with perfect mirrors on the inside, the box suddently has "invariant mass"... exactly in the quantity one could have calculated as relativistic mass of the photon.

What are you talking about? It is EXACTLY so that electromagnetic radiation carries mass away from objects. I hope you are aware that the sun loses mass by fusion. This mass doesn't vanish, but is carried away by the sunlight. If you have a cellphone with a 12.16 Wh battery, and you use it until the battery is empty, it will be a bit lighter: E = mc² 12.16 Wh/c² = 4.87 × 10^-13 kg It is just a miniscule amount, but this mass doesn't vanish into nothingness, but is carried away by electromagnetic radiation (mostly by infrared photons because of the cellphones warmth) An molecule (A) in an excited state is a tiny bit heavier than the same molecule in ground state. If the molecule drops from the excited state into the ground state, it loses that bit of mass. The mass is carried away by the photon. If this photon then hits another molecule (, it may put it into the excited state. Now the second molecule ( is a bit heavier. Molecule A lost mass, and molecule B gained it. The photon transfered the mass between those molecules. If you consider that experiment as a closed system, and you would somehow measure the mass of the system, you wouldn't see a decrease in mass while the photon is between A and B. The System would always have the same mass: - First is molecule A "heavy" and molecule B "light". - Second is molecule A "light", there is a photon with a certain mass, and molecule B is "light" - Third is molecule A "light" and molecule B "heavy" I worked for a while at an antimatter-source at a research reactor. The source produces positrons and electrons out of gamma radiation. positrons and electrons clearly have mass, but were did it come from? It didn't come from nowhere: The gamma photon (just electromagnetic radiation) had this mass before it was turned into the matter-antimatter pair. There are many unknown things in physics, but your claim "There is something more to the puzzle that we haven't figured out yet" is just wrong in relation to the mass of photons. There isn't anything left in that puzzle. It is just that many prefere to not use the label "relativistic mass". From that "purist" perspective photons don't carry mass, because only invariant mass counts. It is really just a semantic and didactic question. The science behind it is clear and without any questions left.

We only need special relativity to answer the question of this thread. And special relativity is perfectly compatible with quantum mechanics. They are already connected. Photons are only massless if you are one of those purists that only count invariant mass as "real mass". If you use the concept of relativistic mass, then photons have a mass: The energy of a photon is dependent of its frequency: E = h f h is the Planck constant. The mass of a system is fundamentally dependent on its energy content: E = m c² So the "mass" of a photon kinda is: m = h f / c² That is consistent with the momentum of a photon. Momentum is defined as: p = m v If we insert the "mass" of the photon and its velocity ©, we get p = h f / c This is exactly the momentum of a photon you can find in every textbook. So the mass of a photon is much more a semantic question than a physical one.