Mystery111
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Posts posted by Mystery111
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I didn't qoute that, so you are misrepresenting the facts.
My post qouted you talking about knowing very little on tachyons, then asking me what a spacelike condition has to do for a tachyon. I explained to you that was one solution I referenced before and if you wanted those references you would need to go back. Secondly I explored a further option.
So qouting me like you did is disingenuous.
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The past is a record of everything that *has happened*. The present is now happening.
It's the only time ever happening. And the past is only a record because our psychology dictates this so. There is no real past, only memories of past events.
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The answer to that is the answer to the thread and I don't think anyone knows.
"Time is (a measurement of) change" is also insufficient, because things can change slowly or quickly (the same amount of change can correspond to different amounts of time), and also it can't be "Time is (a measurement of) rate of change" because the same rate of change be maintained over different amounts of time.
I don't think "change" is the essence of time. Entropy might be. The constancy of the speed of light certainly is related (but if time is defined based on light, it might be cyclical because distance is already defined based on time). If change is expressed in terms of the passing of information across distances, then a definition of time based on change might work.
Personally, I think (so please disregard this as anything more than just an idea) that "time is distance" is true, but as I mentioned distance is based on time. Also, the assumption of isotropic propagation of light makes it false. But if light was anisotropic and time and distance were equivalent, then a non-cyclical definition of time would be defined using something other than distance. My guess would be: Time and distance are emergent measurements of causality's consistency . Or instead of that, maybe something that even makes sense.
Change means motion, Einstein's field equations generate motion in time that is a symmetry of the theory, not true time evolution. So there is a problem with believing the definition of time is change.
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I don't see how that makes sense, but I'm not too familiar with tachyons.
When you say "time-like" do you mean a tachyon that follows a time-like geodesic, because that sounds like a contradiction in terms. Nothing that follows a time-like path would be a tachyon.
There are in fact many models which attempt to deal with the causal nature. For the timelike-spacelike references, I noted them before go back and check.
''It has been argued that we can avoid the notion of tachyons traveling into the past using the Feinberg reinterpretation principle[3] which states that a negative-energy tachyon sent back in time in an attempt to challenge forward temporal causality can always be reinterpreted as a positive-energy tachyon traveling forward in time. This is because observers cannot distinguish between the emission and absorption of tachyons. For a tachyon, there is no distinction between the processes of emission and absorption, because there always exists a sub-light speed reference frame shift that alters the temporal direction of the tachyon's world-line, which is not true for bradyons or luxons. The attempt to detect a tachyon from the future (and challenge forward causality) can actually create the same tachyon and sends it forward in time (which is itself a causal event).''
I actually know a bit about negative energy tachyons. Two negative energy states in the form of two negative energy bispiners are:
[math]\psi_3 = \psi_{-} = N \begin{pmatrix} 1 \\ 0 \\ -a \\ 0 \end{pmatrix}[/math]
[math]\psi_4 = \psi_{-}' = N \begin{pmatrix} 0 \\ -a \\ 0 \\ 1 \end{pmatrix}[/math]
There are two positive energy bispiners as well. The four component bispiner [math]\psi_{\sigma}[/math] comes from the desription for a free particle plane wave with momentum [math]\vec{p}[/math]. Using the wiki article, this would mean that there no way we can destinguish temporal causality between the negative tachyonic description sent back in time as it can be reinterpreted as a postive energy tachyon moving forward in time.
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The speed of light is special because it's invariant. That is what makes c special, and the existence of speeds faster than c would make c no less special in that regard. If something travels FTL in one frame then it travels back in time in another frame -- not because light is the fastest speed of communication, but because it is invariant (the same in every frame).
Highlighted part: agreed.
Non-highlighted part: A timelike tachyon does, not a spacelike tachyon which was the point I was raising earlier. Some models go back as far as the 60's which try to circumvent the problem of a faster than light particle which would oscillate throughout time and the causality problems which closely asist it.
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I wasn't sure what your point was; you seemed to be saying you can get a signal before you send it if you can communicate at the speed of light. That's not true.
I don't see why FTL would somehow negate the causality violation. If the rest of relativity still held, the example given shows how you can violate causality.
I think what he is saying is it still ''takes time'' for a luminal signal to be taken from one point to another. A slightly faster process would be a new ''communication limit'' in his words. In that sense, it could be possible we are just dealing with a new species of particle which moves slightly faster than light, but does not physically oscillate in time. Such models have been constructed for superluminal particles.
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But you must know that true present is not observable. What we believe is present is in fact the past.
_____________
I can't resist to have a look back at my beautiful pencil universe.
The present is a record of the past, with an intuitive mind present.
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"The thing that stops you..." is lack of a series of causal events, as above.
Causation in itself is correct. Though the state vector of a system determines in the probabilistic sense of why you don't suddenly show up in other places. Remember this is strictly the weird yet wonderful nature of quantum mechanics; somehow subatomic objects can be in more than one place at one time, they can also show up great distances away from where they are due to potential vacuum tunnelling. These things aint so apparant on our level, in fact that is an understatement; it is more or less non-existent at our level. So the wave function would be dictating that this behaviour would be improbable for large macroscopic objects, which are themselves modelled causally, as you say.
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I know what you mean. You could be right.
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Some might come to think this. I've often seen definitions where ''time is equated to the ability to change'', and ''time is a measurement of a change of space.''
I suppose you could. I probably wouldn't though, I don't like the idea of equating time to the ability to change because of the quantum mechanics principle of veiwing time as short beginnings and stops. Motion requires a linear notion of time when you measure events next to each other like that. But motion in General Relativity arises as a symmetry of the equations, so perhaps it can be faulty veiwing it directly like this if not careful.
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Sounds interesting. How does that work?
A reinterpretation of tachyons moving back in time was speculated all the way back in the 60's
O. M. P. Bilaniuk, V. K. Deshpande, and E. C. G. Sudarshan,
Am.J.Phys. 30 (1962) 718.
G. Feinberg, Phys. Rev. 159 (1967) 1089.
The other way to avoid causality problems is to introduce a kinematic time under a non-standard form of Lorentz Transformations
R. Tangherlini, Nuov. Cim Suppl., 20 (1961) 1.
P. Caban and J. Rembielinski, Phys. Rev., A 59 (1999) 4187.
Here are the first two
http://prola.aps.org/abstract/PR/v159/i5/p1089_1
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I'll get back to this. Defining time is hard, many different cases to consider than I have free at the moment.
Right now I have enough time... lol... mind the pun.
Let's start with Relativity. I've already spoken about timelessness arising as the time problem of uniting General Relativity with quantum mechanics in another thread, so time might not even exsit according to this theory.
Special relativity is a little more mundane; this theory allows clocks to be moving in a flat spacetime.
Essentially relativistic theories treat time as a ''dimension'' of space. Time actually has two very loose meanings in this context. One is a true real time description Real Time (or also known as imaginary space) or it can be called Real Space (which is imaginary time). Describing your universe or system in either context can be rewarding in physics when viewing the physical world. For instance timelike and spacelike movements are pivotal to understanding how a Bradyon and a Luxon and a Tachyon are all defined as speeds. Bradyons (''brady'' root word meaning slow, also known as tardyons) are spacelike whereas a tachyon (''tachy'' from the root word ''fast'' as in tachycardia) is timelike in nature (though not all tachyons require to be timelike according to some work).
Time in quantum mechanics has many descriptions, some of which are outdated. Newtonian physicists and a few quantum thinkers today still believe that time has a flow. This has been demonstrated in quantum mechanics to be false, there does not seem to be an arrow of time nor does there seem to be a flow associated to events. Instead time in quantum mechanics is more like a set of starts and stops. Tiny momentary fleeting flashing of physical existence which is not tied to any fundamental flow. Time is non-linear, and has a geometry. Time is not an arrow directly drawn from any center in space either because space does not contain your normal definition of ''up'', ''down'' ''left or right''. Nor did the big bang happen in one place alone, in fact big bang happened in all places at once.
So if you are looking for a nice, clean definition of time that is simple, you would certainly be leaving out a lot of details which may provide a clearer definition. A nice easy one would be ''Time is an instantaneous moment or short duration of an instantaneous moment.''
That would be the definition from physics. From Relativity, time may have two descriptions, actually one is a non-description:
1) Time does not exist
2) Time is a measurement of moving clocks
Of course, Relativity may permit a third
3) Time is an instrinsic degree of freedom
Where here ''degree of freedom'' is by definition a dimension.
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I like this to. The problem with it is that one might incur an infinit amount possible outcomes, from one instant of time to the next. I could expect to be on the beach in one instant and the moon the next. I've tried LOL!!! it just doesn't work. The past and present are at the very least a momentum that narrow down logical position and possibility. Like pi dividing out, there is always a next and predictable number and an absolute truth of historical events.
The thing that stops you from suddenly ending up on the moon is more or less due to your wave function which peaks wherever you are right now. My wave function extends far out past our local galaxy, but chance of finding me there is very very very slim.
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This is quite funny.
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Sounds interesting. How does that work?
I'll see if I can find the relevent papers.
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Yes maybe in his opinion he would like to have seen gravitons. We are all under the idea though it was to find the Higgs Boson. Which is still elusive... if it even exists. A lot of people are questioning it now.
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Yes but experimentation clearly shows there is a ''cut-off'' between the micro-world and the macro-world. This may be no larger than let us say a semi-macro object - we've managed to observe quantum wave oscillations to a certain degree without direct observation, but after a certain point the usual quantum weirdness we might associate at the level of electrons and protons begins to dissipate with the larger object you deal with. The Schrodinger Cat experiment can easily be determined not to be the product of two outcomes because we initially believed that the quantum weirdness extends even to our level of every day macroscopic objects, which just isn't the case.
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It turns out you can avoid causality problems for tachyons if you model them spacelike instead of timelike, which is possible.
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Nothing is the meaning of something devoid of description and existence. So how can a universe really be expanding in nothing?
It is a useless statement in itself.
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It's an anecdote acting as a thought experiment. As for what he was proving, just as was said. It was to highlight the descrepency of understanding how quantum systems behave differently to larger masses and how two different outcome can exist due to a wave function.
His experiment has been answered through decoherence. The cat won't be alive and dead at the same time.
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You will have to expand on this a bit.
But why exactly going faster than light upsets cause and effect? Nobody has spelt it out yet.
I have said it in plain English.
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Now you've lost me a bit. Is a tachyon the same as a neutrino?
You have been speculating the recent news that a nuetrino could violate causality. That would mean the neutron would be a tachyon.
I apologize, would mean the neutrino would be a tachyon! See am getting mixed up now!
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Wrong.
If you look at the Lorentz transformations you will find that superluminal speeds result in imaginary time dilation.
Curious, I don't think I said anything about imaginary time dilation. I said it was able to oscillate in the time dimension.
That is to say, it freely able to move into the past and the future, obviously many causality problems arise.
Imaginary time is real space. Real time is imaginary space. Travelling at different speeds lets to travel through these descriptions of time.
Ok, so is it the case that the faster you go the more massive you become and, therefore, the slower you move? That at the speed of light you would become infinitely massive so that no movement or time would exist? If so, how could a particle like the neutrino, which I understand does possess a little mass, get past this barrier? Even a tiny amount of mass would become infinite at light speed, wouldn't it?
No because a tachyon would find the lowest amount of energy available for it at the speed of light. It's the effects of the speed which does not linearly move through the time. This is why when you send a tachyon off on it's journey, it could end up arriving at place before it had been fired.
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The Problem of Time in physics is one born out of the Wheeler de Witt equation. The Wheeler de Witt equation fails to describe the universe with a time evolution because the right hand side of the equation does not contain a time derivative. The Field Equations Einstein derived describe motion in time which arises as a symmetry of the theory, not true time evolution itself [1].
I propose that it is a matter of not being a true time evolution in one case where there are pure gravity solutions to Einstein's equation. By allowing to choose two conformal time descriptions in the Wheeler de Witt equation [math]t = \chi[/math] and [math]\tau = \alpha[/math] you can describe two unique fields which we can use under the true definition of what allows the motion of real clocks to be measured.
To explain this more accurately, it is conjectured that the diffeomorphism contraints on the Hamiltonian of the Universe which leads to the vanishing of the time derivative should be taken as the analogue of a universe with only objects who's frame of reference ceases to exist because of Time Dilation. Chronological description of evolution of events in a universe where relativity treats the parts as moving in the null trajectory leads to no time description. Such a universe could be one with simply a radiation field and no matter at all. In fact, primordially-speaking this was the fundamental makeup of the universe at one point in it's history. It was just a soup of gamma radiation.
Matter Fields and for that matter (fields which defined moving clocks) appeared when a processes of geometrogensis [2] appeared when the universe sufficiently cooled down. Matter at the high energy scale implies the conditions we attribute to the early universe. That means by those calculations, the universe had to cool [math]10^{20}[/math] times less than what it is observed to be today and that high level is the level which quantum gravity is speculated to merge all the forces known to nature. So matter fields are attributed to low energy theories of our universe. In the fundamental theory, Fotini Markopoulou has remarked that geometry will no longer be involved.
On this limit, my theory would be advocating the presence of only radiation fields. Some may find this difficult to still understand because essentially we can only model our known field theories on Langrangian's which is measured in a space [math]dx^3[/math], but Fotini may be closer to the truth than we could realize. Perhaps when we are invoking the laws of physics in higher temperatures we are needing to change the view we are looking at the geometrical properties of the vacuum and how matter becomes manifest from this geometry and curvature.
The application and understanding of how matter fields could alter the way we view a Hamiltonian for a universe described by the state vector [math]|\psi>[/math] may imply the possibility of there being atleast in description, two different outcomes for when time can be logically applied to the Hamiltonian in the normal theories constraints which traditionally tend to favor the time derivative vanishing. To make this work, you must assume that the interaction has two solutions, one which is physical and the other pure radiation.
But before that is even mathematically-presented, anyone familiar with the Wheeler de Witt equation will know it by the form:
[math]\hat{H}|\psi> = 0[/math]
I will present this another way:
[math](H + (\alpha^2 - g^2\alpha^4))|\psi> = \hat{H}|\psi>[/math]
This part [math](\alpha^2 - g^2\alpha^4)[/math] plays the interaction of the Hamilonian. [math]\alpha[/math] for now can be known as a scale factor. The full Hamiltonian of the WDW-equation is
[math]H_{WDW}=H_{T}=H_{\phi, h_{\mu\nu}} - H_0[/math]
This comes from the implicit assumption [3] one imposes conformal time gauge conditions on the Hamiltonian. There is a physical component of the total Hamiltonian, the metric perturbation [math]h_{\mu \nu}[/math] recognized most famously from weak metric limits in General Relativity [4].
In a proceedure of seperation of variables [math]|\psi> = |\phi_\alpha>|\chi_{\phi, h}>[/math] leads to two equations
[math](H + (\alpha^2 - g^2\alpha^4))|\psi_a> = E|\psi_\alpha>[/math]
and
[math](H + (\alpha^2 - g^2 \alpha^4 dt))_{\phi, h}|\chi_{\phi, h} > = E|\chi_{\phi, h}>[/math]
Where [math]\chi[/math] is a matter field acting as time. In fact, in these equations in the superminispace model you can freely choose between using the scale factor [math]\alpha[/math] or the matter field [math]\chi[/math] as your choice of time coordinate. Interestingly, you may be able to break your Hamiltonian into a matter field [math]\chi[/math] and a radiation field [math]\alpha[/math]. You may be allowed toconstruct a time for a universe where real clocks can be measured, but if the constraint lets [math](\alpha^2 - g^2\alpha^4 dt) \rightarrow 0[/math] determine whether it is a massless radiation field, which cannot be used to measure the motion of clocks due to relativity. This means under certain limits matter fields can vanish.
Matter fields are trivial in General Relativity. Trivial scalar fields like a matter field in conformally flat spacetime is in fact a non-gravitating part of the theory. Vanishing matter fields would be akin to pure gravity solutions of General relativity.
Assuming the inertial part [math]\chi[/math] of
[math](H + (\alpha^2 - g^2\alpha^4 dt))_{\phi, h}|\chi_{\phi, h} > = E|\chi_{\phi, h}>[/math]
vanishes when the potential reaches the ground state then you are dealing with two different potentials. You find these potentials as:
[math]\alpha^2-g^2\alpha^4 = V(\alpha)[/math]
for a radiation field [math]a= \tau[/math] and
[math]\chi^2 - g^2\chi^2 = V(\chi)[/math]
For your matter field. You retreive these potential terms by treating the wave function in the WDW-equation as being [math]\Psi(\alpha,\chi)[/math]. If there is an inertial part then you have the presence of a matter field, you obtain the equation
[math](\frac{1}{4} \frac{\partial^2}{\partial \chi^2})\psi_{\chi}(\chi) = E\psi_{\chi}(\chi)[/math]
So in order to solve the Time Problem of Physics resulting from the time derivative vanishing, why don't we just adopt the idea it depends on your choice of restraint and what field you use to try and define your clocks? The only premise that would need to be adopted is that the derivative vanishing as a statement of having your Hamiltonian in two different states: one allowing clocks to be defined in the matter state [math]\psi_{\chi}(\chi)[/math] and for those where relativity naturally does not permit time passing, pure radiation fields [math]\psi_{\alpha}(\alpha)[/math].
[1] - http://www.fqxi.org/...ou_SpaceDNE.pdf
[2] - def - http://en.wiktionary...geometrogenesis
[3] - http://arxiv.org/PS_...3/9503073v2.pdf
[4] - http://ned.ipac.calt...3/Carroll6.html
It might be worth noting that the approach is similar to the construction of the Freidmann equation where it is divided into a radiation part and [math]\rho[/math]-matter part. The radiation part of the pressure is usually ignored because the matter part dominates when a universe begins to cool down.
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Why does FTL imply causality violation?
in Relativity
Posted
Because I said the first part was agreed with, and not confirmed the second part, that was my fault I guess.
I was not disagreeing, I was adding to the different interpretations of tachyons. Nowhere in that reference you made of me:
''Non-highlighted part: A timelike tachyon does, not a spacelike tachyon which was the point I was raising earlier. Some models go back as far as the 60's which try to circumvent the problem of a faster than light particle which would oscillate throughout time and the causality problems which closely asist it.''
Contains anywhere that I disagreed with your post. You brought up causality, which is what is implied by that model you speak of. That is why my reference to the non-highlighted part was in nature of the problem of causality offerring other solutions, which I gave.