Speed of light

[JimJast]

We show that, given current data, the probability that the Universe is spatially infinite lies between 67% and 98%, depending on the choice of priors. For the strongest prior choice, we find odds of order 50:1 (200:1) in favour of a flat Universe when compared with a closed (open) model.

Harry, so what happened to general realtivity in which (correct me if I'm wrong) the space can't be flat since the relative spatial curvature and relative gravitational time dilation have to be equal for general relativity to work (as we observe it while seeing bending of light rays in the vicinity of big masses). Since only then there is no change in total energy of a free falling particle: dE/dx=0 along the whole free fall. If the universe were spatially flat and the gravitational time dilation can't be zero (since Newtonian limit has to be valid) then we have |dE/dx|>0 and where this "additional force" is coming from? It surely can't be a force explained by general realtivity. So what is it? "Spooky action at a distance?"

With what theory of gravitation the boys explain gravitation then if genreal realtivity does not apply to it any more? And when the general relativity got rejected as a theory of gravitation? I hope it is not only the result of this ridiculous hypohtesis of expanding universe since in Einstein's general relativity the universe is not expanding; only in Wheeler's "general relativity" of 1973, one with symmetric metric tensor and creation of energy according to the actual needs of the theory as an axiom that does not need to be proved.

[The Code]

I,m sorry, I really have to ask this question. Like the two jet aircraft, they placed two atomic clocks and they were at different times when they landed. What difference would be the time, if we were able to place one inside the golf ball BB, and 1 in the Space Time at GMT? I know this could never happen.

mark

[apodman]

Sorry, as hard as I try I'm unable to visualize what you're asking. Perhaps others are having the same trouble. Maybe you could rephrase the question.

[harry]

G'day from the land of ozzzzzzz
Hello Mark

It's always in the communication by EMR. You effect the speed of the EMR and the distance you also affect the communication and you will get a difference in time.

[The Code]

If we were some how able to place two clocks at the start of the big bang ,,either side of the universe. So one clock finished up on planet earth and the other finished up on the other side of the universe What would be the time difference in the two clocks. somebody told me once. there would actually be a different time. Thanks harry, i will look it up.

Mark

[harry]

G'day from the land of ozzzzzzz

The time would be the same.

If you tried to communicate than the communication time would have to be taken in the calculation.

As for the BBT, it's only a theory.

[apodman]

This kind of stuff boggles my mind.

The time measured by each clock depends on its history of velocity (in accordance with Special Relativity, a moving clock runs more slowly).

The time measured by each clock also depends on its history of acceleration (in accordance with General Relativity, an accelerating clock runs more slowly).

The time measured by each clock also depends on its history of exposure to gravity (in accordance with General Relativity, a clock subjected to the force of gravity is affected the same way as a clock subjected to an equivalent force of acceleration).

As far as I understand, only velocity and acceleration with respect to an inertial reference frame count, whereas velocity and acceleration calculated from an increase in distance from expansion of space don't count. But don't believe me - I already said my mind was boggled.

As far as I understand, two clocks with identical histories of velocity, acceleration, and exposure to gravity will measure the same passage of time regardless of their separation.

And of course harry is right that you have transmission time to consider when reading the other guy's clock remotely.

Try the following links for some background. Take the information for what it is: the first four descriptions may be diluted, and the fifth in some points may reflect the opinion of the author.

http://en.wikipedia.org/wiki/Hafele-Keating_experiment

http://en.wikipedia.org/wiki/Twin_paradox

http://en.wikipedia.org/wiki/Time_dilation

http://en.wikipedia.org/wiki/Gps#Relativity

http://www.theoryofeverything.co.uk/tim ... ty_theory/

[harry]

G'day from the land of ozzzzzzzzz

Apodman is right,,,,,,,,,,next time apply the KIS principle

[astrolabe]

Hello JimJast,

as we observe it while seeing bending of light rays in the vicinity of big masses

There's an entire thread on just this subject (if not several). And, in reading about your unsuccessful attempts to publish your (Einstein's) view, I believe I could surmise that you do profess an adherence to the fact that space curves. If that is so then how is it that you say that light bends? Doesn't Plank Length forbid it?

[harry]

G'day from the land of ozzz

I was going to respond,,,,,,,,,,but! I have the flu and my head is here and there.

Jimjast can you give me more of an explanation.

Keep it simple for now,,,,,,,,this flu is playing with my thoughts.

[harry]

G'day from the land of ozzzzzzzz

I came acroos this paper

SAO/NASA ADS Astronomy Abstract Service
Simulations of ultrarelativistic magnetodynamic jets from gamma-ray burst engines
Aug-08
http://adsabs.harvard.edu/abs/2008MNRAS.388..551T
http://adsabs.harvard.edu/cgi-bin/nph-d ... db_key=AST

Long-duration gamma-ray bursts (GRBs) require an engine capable of driving a jet of plasma to ultrarelativistic bulk Lorentz factors of up to several hundred and into narrow opening angles of a few degrees. We use global axisymmetric stationary solutions of magnetically dominated (force-free) ultrarelativistic jets to test whether the popular magnetic-driving paradigm can generate the required Lorentz factors and opening angles. Our global solutions are obtained via time-dependent relativistic ideal magnetodynamical numerical simulations which follow the jet from the central engine to beyond six orders of magnitude in radius. Our model is primarily motivated by the collapsar model, in which a jet is produced by a spinning black hole or neutron star and then propagates through a massive stellar envelope.

We find that the size of the pre-supernova progenitor star and the radial profile of pressure inside the star determine the terminal Lorentz factor and opening angle of the jet. At the radius where the jet breaks out of the star, our well-motivated fiducial model generates a Lorentz factor γ ~ 400 and a half-opening angle θj ~ 2°, consistent with observations of many long-duration GRBs. Other models with slightly different parameters give γ in the range 100-5000 and θj from to 10°, thus reproducing the range of properties inferred for GRB jets. A potentially observable feature of some of our solutions is that the maximum Poynting flux in the jet is found at θ ~ θj with the jet power concentrated in a hollow cone, while the maximum in the Lorentz factor occurs at an angle θ substantially smaller than θj also in a hollow cone. We derive approximate analytical formulae for the radial and angular distribution of γ and the radial dependence of θj. These formulae reproduce the simulation results and allow us to predict the outcome of models beyond those simulated. We also briefly discuss applications to active galactic nuclei, X-ray binaries and short-duration GRBs.

[JimJast]

[...] you do profess an adherence to the fact that space curves. If that is so then how is it that you say that light bends? [...]

Imagine yourself sitting in an accelerating vehicle and a straight light ray enters the vehicle perpendicularly to the direction of acceleration. You are then seeing the ray as bent in your (accelerating) frame and it changes direction in relation to the vehicle by certain angle. It turns out that half of this angle is due to the acceleration of the vehicle and another half due to the curvature of space in this vehicle since it was observed also in gravitational field of the Sun by Eddington during a solar eclipse while Eddington was looking for confirmation of Einstein's predictions for gravitational field that Einstein's theory predicted as equivalent to effects in accelerating vehicle. One concludes that the gravitation is the time dilation on one hand and the curved space on the other. One has to go with the other to keep the spacetime intrinsically flat. The result is that if there is no curvature of space there is no gravitation (since there is neither any gravitational time dilation. Which was also noticed by Narlikar, but his suggested physical reason for it (the mass of elementary particles diminishing with time) are a little bit controvercial (non physical, and unnecessary in my opinion).

Jimjast can you give me more of an explanation. Keep it simple for now,,,,,,,,this flu is playing with my thoughts.

More explanation but of what? Here are basics of Einsteinian gravitation: since for the reason of widely known inability of nature to produce energy from nothing (or, since in Einsteinian gravitation there are no "gravitational forces" acting at a distance then dE/dx=0 in free fall, where E is total energy of the particle, some internal =mc^2, some kinetic = whatever, and x is position of the particle in any coordinate frame) the relative curvature of space must be equal to the relative gravitational time dilation, which in the case of an immobilized particle produces, in frame where it is immobilized, "gravitational force" F=(d/dx)[m(v)c^2(x)] where m(v) is relativistic mass of particle, c(x) is coordinate speed of light. If you calculate this Einsteinian gravitational force (as dE/dx=(d/dx)[m(v)]*c^2(x)+m(v)*2c(x)*(d/dx)[c(x)])it turns out to be the same as Newtonian F=mg, where m is mass of the particle, g is gravitational field that shows up when the particle gets immobilized which means that Einstein's theory supplies (almost) the same reasults as Newtonian only when the space curavature is of right value. It can't be zero or anything not corresponding to the gravitational time dilation. It's just a plain and simple Einsteinian physics. So how the space of real universe in which most objects move along (almost) Newtonian trajectories can be flat? Where those Newtonian trajectories would have come from? From what theory of gravitation, if it is not Einsteinian? I hope the question is clearer now but if it is not then ask about particular things that aren't clear.

[astrolabe]

Hello Harry,

You too?!? My brain is a cotton wad and while it doesn't affect my thinking (diminuative at best on a good day) it does affect thought organization- probably not a good time for posting but what the heck! Here goes anyway.

Hello JimJast,

My query was perhaps misunderstood. We all struggle on this Forum with precision in communicating ideas as well as accuracy reading ideas or questions posted by other members. Sometimes I get excited about the concept I'm trying to convey and don't (or can't) slow down enough to be sure my own thoughts connect with those of other members'. I chalk it up to passion but in the past I've been asked on to clarify a point (or twelve!) and found it easier to reread questions and answers before I hit "submit". This is in no way any kind of singular admonition; just passing along a little of my own experience for everyone's benefit. Take it or leave it as you wish.

"You are then seeing the ray as bent in your (accelerating) frame and it changes direction in relation to the vehicle by certain angle"

Isn't this an artifact of perception (coined by Chris P.)? Light eminates, as far as we know, as a sphere in all directions and so light will always appear as a direct line to the source. I'm playing devil's advocate here but an accelerated(ing) body passes through these EM spheres and even if the body's vector angle changes from perpendicular which is nearly always because being perpendicular, at least mathmatically, is a singularity issue and amost never occurs in nature, light will still travel straight.

So IMHO light does not bend...space curves.

"...since for the reason of widely known inability of nature to produce energy from nothing."

True, but in the case of DE I don't necessarily think we can determine the source so to me it is a mental exercise only.

[harry]

G'day from the land of ozzzzz

How do you explain Lensing by compact objects?

[apodman]

If I'm wrong about this, somebody please correct me.

---

Suppose I live on a spherical planet. The 2D surface I walk on is curved positively. If I walk from point A to point B to point C and back to point A, taking the shortest possible (straight, within the rules of the positively curved geometry) route from each point to the next, I trace a triangle whose angles add up to more than 180 degrees. Suppose further that this spherical planet has no hills. I can travel anywhere on the surface of this planet in a line that is straight with respect to the spherical geometry. (Now suppose that this spherical planet has hills. In that case, my shortest route between points with an intervening hill is curved - compared to a straight line in the spherical geometry - to a degree determined by the size of the hill.)

Suppose instead that I live on a Euclidean plane. The 2D surface I walk on is flat. If I walk from point A to point B to point C and back to point A, taking the shortest possible (straight, within the rules of the flat geometry) route from each point to the next, I trace a triangle whose angles add up to exactly 180 degrees. Suppose further that this Euclidean plane has no hills. I can travel anywhere on this surface in a line that is straight with respect to the flat geometry. (Now suppose that this Euclidean plane has hills. In that case, my shortest route between points with an intervening hill is curved to a degree determined by the size of the hill.)

Suppose in yet a third case that I live on a hyperbolic paraboloid (an unbounded saddle shape). The 2D surface I walk on is curved negatively. If I walk from point A to point B to point C and back to point A, taking the shortest possible (straight, within the rules of the negatively curved geometry) route from each point to the next, I trace a triangle whose angles add up to less than 180 degrees. Suppose further that this hyperbolic paraboloid has no hills. I can travel anywhere on this surface in a line that is straight with respect to the negatively curved geometry. (Now suppose that this hyperbolic paraboloid has hills. In that case, my shortest route between points with an intervening hill is curved - compared to a straight line in the hyperbolic geometry - to a degree determined by the size of the hill.)

The difference among the three cases is Euclid's fifth postulate, the "parallel postulate". In flat geometry, there is exactly one line parallel to a given line passing through a given point not on the first line. In positively curved geometry, there are no lines parallel to a given line passing through a given point not on the first line. In negatively curved geometry, there are infinitely many lines parallel to a given line passing through a given point not on the first line. There are other ways of telling whether your geometry is flat, spherical (positively curved), or hyperbolic (negatively curved), but the differences in parallelism and the angles in a triangle are the traditional telltale signs. (Note that hills have the same type of effect on all three geometries.)

---

Now suppose that the universe is spherical space-time. The 4D space-time a photon travels through is curved positively. If a photon travels from point A to point B to point C and back to point A, taking the shortest possible (straight, within the rules of the positively curved geometry) route from each point to the next, it traces a triangle whose angles add up to more than 180 degrees. Suppose further that this spherical space-time has no objects with mass, or has no gravity, or has no General Relativity. A photon can travel anywhere in this space-time in a line that is straight with respect to the spherical geometry. (Now suppose that this spherical space-time has objects with mass, has gravity, and has General Relativity. In that case, the photon's shortest route between points with an intervening object is curved - compared to a straight line in the spherical geometry - to a degree determined by the mass of the object.)

Now suppose instead that the universe is Euclidean space-time. The 4D space-time a photon travels through is flat. If a photon travels from point A to point B to point C and back to point A, taking the shortest possible (straight, within the rules of the flat geometry) route from each point to the next, it traces a triangle whose angles add up to exactly 180 degrees. Suppose further that this flat space-time has no objects with mass, or has no gravity, or has no General Relativity. A photon can travel anywhere in this space-time in a line that is straight with respect to the flat geometry. (Now suppose that this flat space-time has objects with mass, has gravity, and has General Relativity. In that case, the photon's shortest route between points with an intervening object is curved to a degree determined by the mass of the object.)

Now suppose in yet a third case that the universe is hyperbolic space-time. The 4D space-time a photon travels through is curved negatively. If a photon travels from point A to point B to point C and back to point A, taking the shortest possible (straight, within the rules of the negatively curved geometry) route from each point to the next, it traces a triangle whose angles add up to less than 180 degrees. Suppose further that this hyperbolic space-time has no objects with mass, or has no gravity, or has no General Relativity. A photon can travel anywhere in this space-time in a line that is straight with respect to the hyperbolic geometry. (Now suppose that this hyperbolic space-time has objects with mass, has gravity, and has General Relativity. In that case, the photon's shortest route between points with an intervening object is curved - compared to a straight line in the hyperbolic geometry - to a degree determined by the mass of the object.)

The three cases are analogous to the three 2D cases described above, only with more dimensions. (Note that the presence of objects with mass along with gravity and General Relativity has the same type of effect on all three geometries, just as the presence of hills had the same type of effect on all three geometries in the 2D cases described above.)

---

There are a lot of unclear descriptions out there regarding flat versus curved space-time, and there are a lot of unclear descriptions out there regarding the effect of objects with mass, gravity, and General Relativity on the curvature of a photon's path through space-time. These descriptions are so unclear that I can't even tell if the authors are mixing two different concepts, but it appears to me that they are indeed mixing them up.

I think the question about the flatness or curvature of space or space-time and the question about the way mass, gravity, and General Relativity affect the paths of photons are two different questions. I think an opinion that space is flat is not a contradiction of an opinion that a photon's path curves in accordance with the principles of General Relativity.

As I said at the beginning, somebody please correct me if I'm wrong.

[Chris Peterson]

I think the question about the flatness or curvature of space or space-time and the question about the way mass, gravity, and General Relativity affect the paths of photons are two different questions. I think an opinion that space is flat is not a contradiction of an opinion that a photon's path curves in accordance with the principles of General Relativity.

I think your analogies and summary are excellent. It is perhaps incorrect to say that the geometry of the Universe and GR are different questions- they are certainly related (and maybe you aren't saying that, anyway). But in the context I think you were addressing, it is true that the shape of the Universe is an entirely different thing than how space is locally distorted by mass (as described by GR).

[apodman]

I didn't want to get into the relationship between the two questions (I wrote enough already). For starters, it may be absurd to talk about the geometry of space in the absence of mass. But then I'd have to address what I think of Mach's principle (something which, in my humble opinion, no human has done successfully yet - and I'm not likely to be the first).

[Doum]

by apodman on Mon Apr 13, 2009 11:15 pm

"As I said at the beginning, somebody please correct me if I'm wrong."


I dont want to see you being wrong cause i undestand it.

[JimJast]

Now suppose that the universe is spherical space-time. The 4D space-time a photon travels through is curved positively. If a photon travels from point A to point B to point C and back to point A, [...]

How do you imagine traveling back while "the arrow of time...etc."? The time is different from space. It runs only one way. There is a way out of this by assuming that a photon goes from A to B1 and then to C while it may go also from A to B2 and then to the same C. If B1 is different than B2 then the photon show up in the future (point C) with different angle of its vector which shows that there are two different futures. The photon may also show up with two different energies, which suggests to mystics that energy can be "created or destroyed somehow" (somehow is the prefered by mystics way of making something from nothing).

Since creation of something from nothing is possible only in fairy tales and in our banking system the physical spacetime has to be flat. It is an intrinsic feature of Einstein's general relativity replaced by Wheeler in his general relativity with the axiom of expanding space. In Einstein's general relativity the accelerating expansion of space is just an interesting illusion, easily explained by the inability of nature to create energy from nothing (just assume strict conservation of energy and observe what happens to photons: you'll see accelerating expansion of the universe, with parameters as observed by astronomers, however, with little understanding of what's going on, since their general relativity is Wheeler's not Einstein's). So it turns out that physics is much simpler than all those possible (but only mathematically) curvatures of spacetime that you have described. It turns out that we need only the curvature of space. Luckily the spacetime isn't curved. We know from experience that the future is only one (just wait a while and then you'll see for yourself ).

[Chris Peterson]

How do you imagine traveling back while "the arrow of time...etc."? :D The time is different from space. It runs only one way.

Time doesn't run one way. There is a symmetry in how particles move in time, some forwards and some backwards. Our perception of time moving in one direction is quite different from what happens at the quantum level.

[aristarchusinexile]

[quote="astrolabe"]

"...since for the reason of widely known inability of nature to produce energy from nothing." True ... quote]

True? Says who? When was this 'fact' 'decided'?

[aristarchusinexile]

[...] you do profess an adherence to the fact that space curves. If that is so then how is it that you say that light bends? [...]

Imagine yourself sitting in an accelerating vehicle and a straight light ray enters the vehicle perpendicularly to the direction of acceleration. You are then seeing the ray as bent in your (accelerating) frame and it changes direction in relation to the vehicle by certain angle. It turns out that half of this angle is due to the acceleration of the vehicle and another half due to the curvature of space in this vehicle since it was observed also in gravitational field of the Sun by Eddington during a solar eclipse while Eddington was looking for confirmation of Einstein's predictions for gravitational field that Einstein's theory predicted as equivalent to effects in accelerating vehicle. One concludes that the gravitation is the time dilation on one hand and the curved space on the other. One has to go with the other to keep the spacetime intrinsically flat. The result is that if there is no curvature of space there is no gravitation (since there is neither any gravitational time dilation. Which was also noticed by Narlikar, but his suggested physical reason for it (the mass of elementary particles diminishing with time) are a little bit controvercial (non physical, and unnecessary in my opinion).

Jimjast can you give me more of an explanation. Keep it simple for now,,,,,,,,this flu is playing with my thoughts.

More explanation but of what? Here are basics of Einsteinian gravitation: since for the reason of widely known inability of nature to produce energy from nothing (or, since in Einsteinian gravitation there are no "gravitational forces" acting at a distance then dE/dx=0 in free fall, where E is total energy of the particle, some internal =mc^2, some kinetic = whatever, and x is position of the particle in any coordinate frame) the relative curvature of space must be equal to the relative gravitational time dilation, which in the case of an immobilized particle produces, in frame where it is immobilized, "gravitational force" F=(d/dx)[m(v)c^2(x)] where m(v) is relativistic mass of particle, c(x) is coordinate speed of light. If you calculate this Einsteinian gravitational force (as dE/dx=(d/dx)[m(v)]*c^2(x)+m(v)*2c(x)*(d/dx)[c(x)])it turns out to be the same as Newtonian F=mg, where m is mass of the particle, g is gravitational field that shows up when the particle gets immobilized which means that Einstein's theory supplies (almost) the same reasults as Newtonian only when the space curavature is of right value. It can't be zero or anything not corresponding to the gravitational time dilation. It's just a plain and simple Einsteinian physics. So how the space of real universe in which most objects move along (almost) Newtonian trajectories can be flat? Where those Newtonian trajectories would have come from? From what theory of gravitation, if it is not Einsteinian? I hope the question is clearer now but if it is not then ask about particular things that aren't clear.

I must muse on the possibility that Jim may be explaining why Galaxies trail their spirals when viewed face on, but are flat discs (save for the centre buldge) when viewed edge on .. we actually see the effects of time revealed in the instant.

[aristarchusinexile]

" ... Since creation of something from nothing is possible only in fairy tales and in our banking system ...)

and through a quantum fluctuation.

[aristarchusinexile]

How do you imagine traveling back while "the arrow of time...etc."? The time is different from space. It runs only one way.

Time doesn't run one way. There is a symmetry in how particles move in time, some forwards and some backwards. Our perception of time moving in one direction is quite different from what happens at the quantum level.

Chris .. I am astounded and astonished and any number of exclamatory descriptive words begining with a and describing astonishing surprise! You and I actually agree on something! And they said it wasn't possible.

[aristarchusinexile]

As far as I understand, two clocks with identical histories of velocity, acceleration, and exposure to gravity will measure the same passage of time regardless of their separation.

The clocks might have to be exactly identical, made of the exact same molecules assembled in the exact same pattern. Of course this is possible in non-locality. Or with locality or non locality .. chance might come into play either way .. either to time the clocks together, or to cause disparity. "Time and chance happen to all men."