The Alcubierre faster than light warp drive

originally posted by: Degradation33
a reply to: rounda

If we could build a ship to travel at 99.999999999999% the speed of light, with 12 decimal places, a person could travel the 2.5 million lightyears to Andromeda and only experience .35 TIME DILATED years.

To that, I can't say anything other than take it up with relativity.

We can't though. So....

What we CAN do is observe light.

And we know that light moves at the speed of light.

And we know that moving at the speed of light, light does not travel instantaneously from point a to point b.

Argue theoretical junk all you want.

We have a real-world observable, and it doesn't do what you claim it should....

So......

And if I'm not mistaken, relativity is based on the idea the speed of light is constant. Which it isn't....

originally posted by: rounda
And if I'm not mistaken, relativity is based on the idea the speed of light is constant. Which it isn't....

I think you are mistaken when you say "which it isn't", though you're correct about the first part that relativity is based on the speed of light being a constant, or more specifically, here is more or less how Einstein phrased the two postulates of special relativity:

2 Postulates of Special Relativity

1. The laws of physics, including electromagnetism, are the same in all inertial frames.
2. Every observer measures the same value c for the speed of light (in vacuum) in all inertial frames.

By the way, relativity only applies to "normal" space ships. The speculated alcubierre warp bubble is sort of able to "bypass" special relativity by creating a separate space-time in the warp bubble, or so the hypothesis goes. Whether such a thing is possible has yet to be demonstrated, and it may not be possible, because you can go on a diet all you want but no matter how much weight you lose, your weight will never, ever be less than zero, yet it's such a negative mass that allegedly can create the alcubierre warp bubble.

originally posted by: Arbitrageur

originally posted by: rounda
And if I'm not mistaken, relativity is based on the idea the speed of light is constant. Which it isn't....

I think you are mistaken when you say "which it isn't", though you're correct about the first part that relativity is based on the speed of light being a constant, or more specifically, here is more or less how Einstein phrased the two postulates of special relativity:

2 Postulates of Special Relativity

1. The laws of physics, including electromagnetism, are the same in all inertial frames.
2. Every observer measures the same value c for the speed of light (in vacuum) in all inertial frames.

By the way, relativity only applies to "normal" space ships. The speculated alcubierre warp bubble is sort of able to "bypass" special relativity by creating a separate space-time in the warp bubble, or so the hypothesis goes. Whether such a thing is possible has yet to be demonstrated, and it may not be possible, because you can go on a diet all you want but no matter how much weight you lose, your weight will never, ever be less than zero, yet it's such a negative mass that allegedly can create the alcubierre warp bubble.

"Which it isn't" means the speed of light is not a constant. Because it's not.

And yes, there is a distinction between Special Relativity, and General Relativity, wherein Special Relativity is localized and General Relativity is outside of "local."

But see, here's the thing. General Relativity can never be tested. It can never be proven. It can never even be observed.

In fact, he had to basically turn gravity into magnetism in order for it to work... and the whole reason he needed to come up with General Relativity was because Special Relativity didn't work with gravity.

Well I hope the "wrap" comes with mayo and some kind of ranch sauce...

On topic... methinks science has established the necessary already.

originally posted by: rounda
"Which it isn't" means the speed of light is not a constant. Because it's not.

What makes you think the speed of light in a vacuum is not constant?

But see, here's the thing. General Relativity can never be tested. It can never be proven. It can never even be observed.

It may not be possible to "prove" anything with certainty, and general relativity may not be an ultimate theory, but so far it has been tested and observed test results match the theory. Some tests are discussed here:

Experimental tests of General Relativity

This is another experimental observation consistent with GR that I'm rather impressed with:

Relativity and Optical Clocks

Another consequence of Einstein's theory is that time runs more slowly in a deeper gravitational potential. For example, if two identical clocks are separated vertically by 1 km near the surface of the earth, the higher clock emits about 3 more second-ticks than the lower one in a million years. These consequences of relativity have been observed with atomic clocks at high velocities and with large changes in elevation. Previously, smaller relativistic shifts could only be seen in short-distance γ-ray Mössbauer spectroscopy measurements. Here we compare two optical atomic clocks to observe time dilation from relative speeds of less than 10 m/s and changes in height of less than 1 m. This sensitivity to small relativistic clock shifts is enabled by recent accuracy improvements...

I'm impressed by the incredible accuracy of those clocks to make such precise measurements of time dilation when the height of the clock only changes by 1 meter or even a little less than that. Some of the old time dilation tests flying atomic clocks on airplanes like the Hafele–Keating experiment seemed rather cumbersome in comparison, but those results too were consistent with special and general relativity.

a reply to: rounda

But see, here's the thing. General Relativity can never be tested. It can never be proven. It can never even be observed.

Are you sure?

You got the part about GPS satellites? Anything that needs a precise measurement.

I don't know what constitutes proof or observation for you, but I'm pretty sure a slightly red-shifted satellite qualifies as a demonstration of relativity.

The code inside the GPS satellites use the equation, plus some other variables, to calculate their individual amount of experienced time dilation. The satellites experience around 7 microseconds of 'delay' every 24 hours due to their speed.

Change in time equals rest time over the square root of 1 minus velocity squared over the speed of light squared.

This:

That's a plug and play equation for time dilation that works everywhere it's needed. You can prattle about general relativity not being proven all you want, but still be left to explain why all satellites have to account for the "theory" of relativity to keep precise time.

So why do satellites need to account for time dilation if relativity is BS? If relativity can never be tested why do satellites in orbit experience less time than clocks on earth and need to be compensated for?

If not "RELATIVE VELOCITY TIME DILATION" what else could it be?

originally posted by: Degradation33
a reply to: rounda

But see, here's the thing. General Relativity can never be tested. It can never be proven. It can never even be observed.

Are you sure?

You got the part about GPS satellites? Anything that needs a precise measurement.

I don't know what constitutes proof or observation for you, but I'm pretty sure a slightly red-shifted satellite qualifies as a demonstration of relativity.

The code inside the GPS satellites use the equation, plus some other variables, to calculate their individual amount of experienced time dilation. The satellites experience around 7 microseconds of 'delay' every 24 hours due to their speed.

Change in time equals rest time over the square root of 1 minus velocity squared over the speed of light squared.

This:

That's a plug and play equation for time dilation that works everywhere it's needed. You can prattle about general relativity not being proven all you want, but still be left to explain why all satellites have to account for the "theory" of relativity to keep precise time.

So why do satellites need to account for time dilation if relativity is BS? If relativity can never be tested why do satellites in orbit experience less time than clocks on earth and need to be compensated for?

If not "RELATIVE VELOCITY TIME DILATION" what else could it be?

That's special relativity... And they figured out it doesn't work unless gravity moves at or faster than the speed of light.

originally posted by: Arbitrageur

originally posted by: rounda
"Which it isn't" means the speed of light is not a constant. Because it's not.

What makes you think the speed of light in a vacuum is not constant?

Scientists proving it isn't.

originally posted by: rounda

originally posted by: Arbitrageur

originally posted by: rounda
"Which it isn't" means the speed of light is not a constant. Because it's not.

What makes you think the speed of light in a vacuum is not constant?

Scientists proving it isn't.

I must have missed that, care to enlighten me with some details?

Wasn't Albert an Einstein a scientist? His theory of relativity proposed it is, and I read about are experiments confirming relativity, which implies a confirmation that speed of light in a vacuum is constant.

a reply to: rounda

Yeah ill go with Arbitrageur and ask for a citation on that... as a Particle Physicist the speed of light not being constant would have made some pretty huge headlines... the last FTL headlines where about neutrinos, tho in that case it was a dodgy cable in a GPS system tagging the time of flight incorrectly.

Also, gravitation, or at least how we witness it, its a pretty good bet it travels with the speed of light. Gravitational waves from compact object mergers are measured in a manner that fits with them moving with a finite speed

a reply to: rounda

That's special relativity... And they figured out it doesn't work unless gravity moves at or faster than the speed of light.

S#. I did say general relativity. My mistake.

The velocity dilation is special, the gravity well dilation is general. Both effect the clock on the satellite in orbit though.

But now I'm just confused by your answer.

Since when does gravity move slower than the speed of light? It's (likely) a force carried by a tensor boson. Massless, like the gluon (strong) and photon (electromagnetism).

Massless things must move EXACTLY the speed of light. The Gravity waves measured by LIGO observing colliding neutron stars and black holes confirmed they exist.

The first direct observation of gravitational waves was made on 14 September 2015 and was announced by the LIGO and Virgo collaborations on 11 February 2016.[3][4][5] Previously, gravitational waves had been inferred only indirectly, via their effect on the timing of pulsars in binary star systems. The waveform, detected by both LIGO observatories,[6] matched the predictions of general relativity[7][8][9] for a gravitational wave emanating from the inward spiral and merger of a pair of black holes of around 36 and 29 solar masses and the subsequent "ringdown" of the single resulting black hole.

en.m.wikipedia.org...

Gravity Waves = gravitational force moving at speed of light.

Pretty much everything Einstein said has been repeatedly confirmed. He's been wrong though. He thought gravitational waves would never be observed.

Many think the graviton will never be detected. Unlike the Higgs-Boson, it will remain unconfirmed. Only one left though. It would be weird for that to be the one thing about the standard model that wasn't confirmed.

Care to regroup and take another whack at this?

The big issue with most of the statements made on this thread is that the assumption is that these apparent observations are interstellar craft.
None of these UAPs may have the power to travel between star systems.
There may only be a couple mother craft that travel between systems, and what is seen is short range craft used for exploration/studies.

www.sciencenews.org...

Remember my post? remember me saying that modifications to the speed of light are entirely because of group velocity changes...

That is exactly what is happening in the reported work. Its actually a bit of a dodgy use of the term 'free space' because its not the same as saying in vacuum, and then in the fluff article you posted it talks about vacuum which, even in the experiment they describe, doesn't exist. They use light passed via a fibre and light that goes through some modification and then back to a target, they then describe that they should arrive at identical times and they dont.

What it is saying is that they can make a beam, a Bessel beam, and control the spacial constraints of the beam, refocus it and it will modify the group velocity. Im actually not at all shocked by that, knowing a bit of optics. Its not the smoking gun you think it is though.

again... its interesting in an optics kinda way, but its not proving the fundamental constant C is being changed... its the group velocity.

Group Velocity, Group Velocity, Group Velocity,

a reply to: ErosA433
Yes so the point is, the speed of light in a vacuum is constant.
You mention group velocity, and phase velocity can also vary from c, but neither group velocity nor phase velocity deviating from c implies that the speed of light in a vacuum is not constant:

Phase, Group, and Signal Velocity

The velocity of a wave can be defined in many different ways, partly because there are many different kinds of waves, and partly because we can focus on different aspects or components of any given wave. The ambiguity in the definition of "wave velocity" often leads to confusion, and we frequently read stories about experiments purporting to demonstrate "superluminal" propagation of electromagnetic waves (for example). Invariably, after looking into the details of these experiments, we find the claims of "superluminal communication" are simply due to a failure to recognize the differences between phase, group, and signal velocities.

As that article also explains, we can even make standing waves, but that doesn't mean the light has stopped moving!

originally posted by: rounda
www.sciencenews.org...

There are quite a few articles like that talking about light not traveling at the speed of light, but when it's in a vacuum they are all talking about things like group velocity or phase velocity, which the science writer you cited didn't even mention, maybe because he thinks his non-physicist readers won't know what those terms mean? They are explained in the link above if you're not familiar.

Anyway, this is why you never trust what the science writer says. If you want to know what's really going on, read the actual paper by the physicists and when you do that they specifically mention group velocity as Eros says:

Photons that travel in free space slower than the speed of light

We study the group velocity of single photons by measuring a change in their arrival time that results from changing the beam's transverse spatial structure.

You can play all sorts of tricks with group velocity, you can even make it faster than the speed of light, but it's a change in group velocity, and you can't send any information faster than light just because the group velocity is faster than light. I've seen science writers confuse that topic too, and claim we can send information faster than light when the group velocity is faster than light, but it's not true and the scientists don't claim that, just the science writers who don't understand what they are writing about very well.

Another interesting thing or analogy of group velocity iv heard said (from way back when i was doing my University Astro courses) was that an example of it is the rotation of spiral arms in a galaxy.

That the appearance of spiral arms is more a function of the formation of young, bright, blue stars than it is a true density change. And that the spiral, does not travel at the same speed as the stars. That the spiral actually travels faster than the stars do.

Hand on heart... I am paraphrasing a super old memory from about 20 years ago, so i may have got that backwards. Regardless its to do with in the case of stars the velocity of the observable over the velocity of the carrier. in a very hand wavy way.

actually
quick google, seems im right
ned.ipac.caltech.edu...

a reply to: ErosA433
This was discussed in my "Ask any question about physics" thread linked in my signature on page 256, where I posted this diagram:


That illustrates how spiral arms can form from elliptical orbits of stars in spiral galaxies, though only about 10% of spiral galaxies are so-called "grand-design spirals" with 2 large arms like that, some spiral galaxies have 4 arms, and in some the arms are less regular.

As your source says you are essentially correct, though I would phrase a couple of things differently for clarification. I didn't post this before, this is the explanation of that theory from page 967 of An Introduction to Modern Astrophysics 2nd ed - B. Carrol, D. Ostlie (Pearson, 2007)


The way we know the spirals are an emergent wave property is because of the "winding problem" discussed at the top of that page, that would occur if the velocity of the spirals resulted from the velocity of the stars with overdensity regions.

I would clarify your mostly correct statement that the new star formation plays a major role in the appearance of the spirals arms, though to the extent it implies that overdensity regions don't also contribute to the spiral arms, I'm not sure that's true, I think it's a combination. I look at a sequence of causalities like:

-Why do the spiral arms look so bright? Partly because of new star formation...
-Why are there so many bright short-lived stars forming in these spiral arm regions? Because of overdensity regions causing their formation...
-Why is there overdensity in the spiral arm regions? See the elliptical orbits diagram showing how overdensity regions occur...
-Why are the orbits elliptical? I'm sure there's a reason for that too (aside from few orbits having zero eccentricity, some kind of many-body gravitational interaction perhaps), but given the variation in spiral arm galaxies, I think it gets more complicated in the details.

The last point I would clarify is whether the stars travel faster, slower, or the same speed as the spirals. We already discussed the winding problem so all stars can't be going the same speed as the spirals, but the Lin-Shu density wave theory shown above suggests there is a particular radius, called the corotation radius, denoted Rc, where the stars actually do travel at the same speed as the spirals. However this doesn't create the "winding problem" given the small fraction of stars at radius Rc, since the vast majority of stars will be at a greater or lesser radius than Rc.

So according to this theory, stars orbiting at radius less than Rc will move faster than the spiral arms, and stars orbiting at radius greater than Rc will move more slowly than the spiral arms. So it is easy to get confused about whether the stars are moving faster or slower than the spirals, when the answer is "yes, to both, depending on where they are"

Another reason I think true overdensity might contribute to the spiral arm brightness, in addition to the new bright star formation, is that we see brighter density waves in saturn's rings, and no new stars are forming there, they are regions of higher density that reflect more sunlight.

An article about density waves in Saturn's rings in "nature" is also linked in the link above. Those Saturn ring density waves too, are emergent, and do not travel at the same speed as the objects in the rings.

So yes I think density waves also provide an analogy of how waves can emerge with different velocities than the underlying phenomena creating the waves.

I think you are right, my wording is a bit rubbish. And there has to be a density role in all of it since the brighter spiral arms are from star formation, which occurs in a process of creation and rapid distruction, which ultimately seed space ahead and behind with material, creating a sort of shock front. BUT thats on the smaller scale rather than grand galactic scale.

The winding problem is also lessened by the fact we know the outer regions orbit too quickly, prompting to the speculation that galaxies are bathed in a dark matter halo. BUT yeah.

great clarification post there above, thanks very much for the addition.

Another addition is that observation suggests that spiral galaxies are probably formed due to close interactions between other galaxies or dwarf ellipticals. The milky-way is a good example, with the Magellanic clouds being a bit of a smoking gun for a recent merger event that was not enough to hugely disrupt the galaxy but possibly drive the fact that the disk is apparently not flat, but wavey, not to mention the spiral arms.

If im also not mistaken, more low redshift galaxies are spirals than they are elliptical, pointing to it being maybe an evolutionary state, either by elliptical orbits as you point out, interaction, or the dark matter contribution which, for an object that is bound but spinning too fast, will always tend to flatten as it represents a lowest energy formation once you age an object and have its constituent parts transfer momentum to get to a lower potential.

a reply to: ErosA433

Sure, if you think you know all the stuff light travels through in space.

It's pretty telling that Einstein explained the flaws in special relativity, and then had to postulate general relativity in order to try to solve the problems with special relativity...

Meanwhile, Tesla believed in magnetism and aether, which is what special relativity basically was. Pretty sure Einstein said there had to be an aether, too.

But whatever.

but ultimately in space, we know what light passes through...

most of the time it passes through better vacuum than we can ever dream of producing on earth.

Im also not sure what exactly you are insinuating by saying "its pretty telling" the theory has been put to the test many times and every single time so far its coming up trumps. The last one i recall (at least the last one which i thought, wow cool!) Was close passes of stars orbiting SagA* which, from theory should experience red and blue shift not only only from movement but from the gravitational well too... and... well it matched very well.

If your postulates are entirely centred on "but light doesn't always travel the speed of light!" so it has to be utterly variable... it simply doesn't hold water as a thing. If the speed of light was so floating, most of astronomy and atomic physics as we know it, well, we simply wouldn't know it because it would be total chaos.