## Can a vacuum have a speed?

Discussions on classical and modern physics, quantum mechanics, particle physics, thermodynamics, general and special relativity, etc.

### Can a vacuum have a speed?

I assume if you have a train made of glass the speed of the slowed light through the glass can be sped up by the speed of the train (relative to an outside observer) according to the velocity combination law. Similarly, if the train was a hollow tube closed at both ends, then the speed of light through air would also be affected by the speed of the train relative to a stationary observer. Of course the velocity combination law would prohibit the train's speed from pushing the light speed within the tube as seen by an outside observer beyond the speed of light in a vacuum. If the train was a hollow tube with open ends, the speed of the train would have no effect on pushing the slower c through air. But if the train was a vacuum tube with closed ends, and you could somehow create slowed light in a vacuum, would the speed of the train boost the speed of that slowed light in a moving vacuum relative to a stationary observer? Is the speed of the vacuum in side the tube the same as the speed of the vacuum outside the tube?

I'd say the answer is yes, one vacuum could have speed relative to an outside vacuum but the velocity combination law and the impossibility of slowed light in a vacuum render the question moot.
ralfcis
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### Re: Can a vacuum have a speed?

Hmmm, I thought there'd at least be some pushback from those who don't believe that light (an electromagnetic wave) uses an electromagnetic medium for propagation.
ralfcis
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### Re: Can a vacuum have a speed?

This is a nonsensical question. Vacuum is not something that can have a speed.

As far as the relative speed of light in a relatively moving glass is concerned, you just need the relativistic addition formula,
$\large v_{lg} =\frac{v_{train}+0.66c}{1+0.66 v_{train}/c}$
which is always < c.
Last edited by BurtJordaan on March 10th, 2017, 5:18 am, edited 2 times in total.
Reason: typo

BurtJordaan
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### Re: Can a vacuum have a speed?

As far as the relative speed of light in a relatively moving glass is concerned, you just need the relativistic addition formula,

different from my statement:

Of course the velocity combination law would prohibit the train's speed from pushing the light speed within the tube as seen by an outside observer beyond the speed of light in a vacuum.

Because you may see similar questions you assume that my questions are the same as one's you've seen before. They are not and you should be able to see that from me agreeing to answers that apply to those questions.

Let me put it another way. If the speed of some kind of electromagntic radiation could be slowed in a vacuum and if you turned on a flashlight of this special slowed electromagntic radiation inside a long sealed vacuum tube, would the electromagntic radiation follow the relativistic velocity combo law because its electromagnetic vacuum medium was moving relative to the outside space or, since so many assume that light has no medium, would the slowed electromagnetic radiation in a moving vacuum tube be unaffected by the moving sealed vacuum it is traveling in when measured by an outside observer.

The question asks is a vacuum an electromagnetic medium for an electromagnetic wave or does light have no medium (even though its speed is suspiciously due to two electromagnetic constants of permittivity and permeability).

The 2nd question is, assuming space is empty (which it is not but most think it is), can nothing inside a tube be really moved if there's nothing to move inside the tube? (Yes I understand the tube can move but can the lack of contents inside the tube be moved if there's nothing to move?)

If you're not picking up on the subtleties of the question because they're outside of relativity, feel free to banish it into the personal theories section. I'm used to that and it's not like anyone here is going to debate this question.
ralfcis
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### Re: Can a vacuum have a speed?

Hi ralfcis,

I get you and of course, the velocity of the leading edge of a light flash would be identical, inside the tube or outside the tube. One can't isolate themselves from Space-Time anymore than one can isolate themselves from Gravity.

If the Space-Time is Curved (compressed) outside the Tube, then it is identical with the inside of said Tube.

Notice how I snuck in the definition of Curved Space as not being bent but rather compressed? Space-Time can be Twisted, Compressed or Stretched because Space-Time vacuum is a Continuum made of discrete information processing components and Matter-Energy is the information being processed by said components.

It's not empty.. but (IMHO) is rather the most Solid Thing in the Universe. It's the underlying foundation for everything that Exists.

If one could figure out a way to removed a chunk of this foundation, then nothing (Matter/Energy/Light) could pass through this missing chunk of Space-Time.

Particles are not little chunks of stuff.. they are purely information being propagated by the processing aspect of the Space-Time continuum.

Again.. just to be clear.. this is my Opinion and hasn't been fully accepted by Canon Science (Yet).

Regards,
Dave :^)

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### Re: Can a vacuum have a speed?

See now that's a specific answer/opinion to a specific question. This kind of answer pretty much doesn't exist on physics forums. It's always some general regurgitation of some unrelated facts or a link to every fact ever discovered. When I criticize this, people get offended because they honestly think they're trying to help and I'm being ungrateful. Just bizarre.

Dave I will digest your answer. It's plausible but I'm hoping none of it is true.
Last edited by ralfcis on March 10th, 2017, 11:03 am, edited 1 time in total.
ralfcis
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### Re: Can a vacuum have a speed?

It's always some general regurgitation of some unrelated facts or a link to every fact ever discovered.

Yeah, I hate it when physics people start bringing facts into a discussion. Ew.

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### Re: Can a vacuum have a speed?

ralfcis » 10 Mar 2017, 14:42 wrote:How is your statement

As far as the relative speed of light in a relatively moving glass is concerned, you just need the relativistic addition formula,

different from my statement:

Of course the velocity combination law would prohibit the train's speed from pushing the light speed within the tube as seen by an outside observer beyond the speed of light in a vacuum.

Of course they are different - the speed through moving glass vs. the speed through moving air. ;)

I assumed your that final paragraph:
I'd say the answer is yes, one vacuum could have speed relative to an outside vacuum but the velocity combination law and the impossibility of slowed light in a vacuum render the question moot.

justified no further comment.

Now you are asking more pertinent questions and maybe someone has an answer for you...

BurtJordaan
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### Re: Can a vacuum have a speed?

Must be a heavy fog obscuring some of my words so if I asked is it going to be sunny this afternoon, the type of response I'd get here is a link to a wiki article about newly discovered solar systems or beavers chew wood. See these are facts but not responses to a specific question. I knew almost no one would understand a word I was saying about the type of responses that are typical on a physics forum. But I am grateful to Jorrie for sticking it out long enough for me to address my problems with relativity just fine in Ralf logic that can co-exist with relativity grudgingly.
Last edited by ralfcis on March 10th, 2017, 11:05 am, edited 1 time in total.
ralfcis
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### Re: Can a vacuum have a speed?

Of course they are different - the speed through moving glass vs. the speed through moving air. ;)

I see the wink at the end so I don't know if you're kidding. But in case you're not, the whole context of the question was does slowed light (an electromagnetic wave in an electromagnetic medium) respond like any mechanical wave to the speed of its mechanical medium. And I listed a number of examples of mediums. Dave's answer is that the medium of space permeates through the glass enclosure of my vacuum like gravity permeates all space enclosed or not. I proposed an answer in my OP and I take it you agree with it although, like I said before, I'm never sure that anything we agree on will survive to the next post.
ralfcis
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### Re: Can a vacuum have a speed?

ralfcis » 10 Mar 2017, 14:42 wrote:Yes I understand the tube can move but can the lack of contents inside the tube be moved if there's nothing to move?

Another moot question: "can nothing move?"

The more interesting question was:
The question asks is a vacuum an electromagnetic medium for an electromagnetic wave or does light have no medium (even though its speed is suspiciously due to two electromagnetic constants of permittivity and permeability)?

The medium is spacetime, as Dave_O said. What is spacetime? Depends on at what level you want your answer: SR, GR, QTF, M-theory, Dave_O theory, and so on...

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### Re: Can a vacuum have a speed?

ralfcis » 10 Mar 2017, 17:00 wrote:I proposed an answer in my OP and I take it you agree with it although, like I said before, I'm never sure that anything we agree on will survive to the next post.

Some advice: never assume silence means anybody agrees with a statement!

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### Re: Can a vacuum have a speed?

But space isn't nothing so I guess a more precise question is can an electromagnetic medium move. Strip away everything people believe space contains and just consider it's an electromagnetic medium. That medium has the measurable characteristics of permeability and permittivity which define it as a substance just like air or glass is a substance with different values for those constants. Nothing doesn't have any values attached to it. I can't answer if stripping away everything space is made of will also strip away those constants but that still irrelevant because the question can be re-asked can the electromagnetic characteristics of a medium move against the backdrop of the electromagnetic characteristics of the background electromagnetic characteristics of spacetime. Does the speed of slowed light propagating through glass remain unchanged by the speed of the glass because the electromagnetic medium of the glass is pegged to spacetime or does the velocity combo law take effect and light is no different than any other wave in a medium.
Last edited by ralfcis on March 10th, 2017, 11:27 am, edited 1 time in total.
ralfcis
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### Re: Can a vacuum have a speed?

Some advice: never assume silence means anybody agrees with a statement!

I don't even though I wish it were true. You did not answer with silence, you answered that you thought my saying it was a moot point was the end of the discussion. I got silence at first and came back wondering why there was no pushback. So I have to ask, yes or no, did you or did you not agree with the statement:

I assumed your that final paragraph:
I'd say the answer is yes, one vacuum could have speed relative to an outside vacuum but the velocity combination law and the impossibility of slowed light in a vacuum render the question moot.

justified no further comment.
ralfcis
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### Re: Can a vacuum have a speed?

Braininvat » March 10th, 2017, 9:14 am wrote:
It's always some general regurgitation of some unrelated facts or a link to every fact ever discovered.

Yeah, I hate it when physics people start bringing facts into a discussion. Ew.

Especially as the facts are so hard to understand --- and to explain?.

Ralfcis, I kept starting to ask you a question and I kept telling myself that "physics dummies" should just keep quiet and let physics experts carry on. But, having just read you latest, I must stick my neck out and get it knocked down.

Question: Exactly where is this "vacuum outside a vacuum"? Is it two sealed vacuums side by side in a pocket of air? Or is it a vacuum inside of a larger vacuum? If the first, how can they relate and, supposing light can travel through a vacuum, wouldn't it travel at the same speed in each of them? If the second, that's a whole new ball game.
vivian maxine
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### Re: Can a vacuum have a speed?

Ralfcis, I kept starting to ask you a question and I kept telling myself that "physics dummies" should just keep quiet and let physics experts carry on.

For such a well established theory like SR, there sure seems to be a lot of debate about it. Whether it's because it isn't explained properly, or too many think memorizing is the same as understanding or there is something wrong with the theory (I do even though I accept all the facts the theory tries to tie together in a cohesive story), I'd prefer to discuss an open-mined question over a close-minded answer.

Exactly where is this "vacuum outside a vacuum"?

It's a long glass tube in space. You seal the ends of the tube with a flashlight inside but the flashlight doesn't shine light, it shines some mythical slower than light electromagnetic radiation that propagates through the electromagnetic medium inside the sealed tube. If you fire the tube out of a space cannon, I'd expect the speed of that slow light in the tube would add relativistically to the speed of the space medium in the tube. But what if you can't seal off space medium just like you can't seal off gravity in a tube. Then the speed of that slow light will not add to the speed of the space medium in the tube.
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### Re: Can a vacuum have a speed?

Thank you. Of course, I'm still confused. I thought you had two vacuum tubes, the second being "outside" the first. If I am misreading, tell me. Then give me a few hours to think.
vivian maxine
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### Re: Can a vacuum have a speed?

Nope the vacuum of space outside separated from the vacuum of space inside.
ralfcis
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### Re: Can a vacuum have a speed?

ralfcis » 10 Mar 2017, 17:26 wrote:So I have to ask, yes or no, did you or did you not agree with the statement:

I'd say the answer is yes, one vacuum could have speed relative to an outside vacuum but the velocity combination law and the impossibility of slowed light in a vacuum render the question moot.

I have answered this in my very first post in this thread.
Vacuum is not something that can have a speed.

Perhaps, if you instead of complaining about the style of the answer, have paid more attention to the content, you would not have needed to ask again. ;)

BurtJordaan
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### Re: Can a vacuum have a speed?

Ok so if you have particles popping in and out of existence from a vacuum in a tube and you could plot the distance between where the particles pop out then pop back, you're saying suddenly moving the tube would not affect that normal separation. So you agree with Dave, the vacuum inside the tube is pegged to the vacuum outside the tube? It's not a leading question, as I'm not sure of the answer, but it does affect my understanding of relativity.
ralfcis
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### Re: Can a vacuum have a speed?

ralfcis » March 10th, 2017, 12:00 pm wrote:Nope the vacuum of space outside separated from the vacuum of space inside.

Oh! All right! Now I have it. I seem to forget that outer space is a vacuum. And were it not for gravity, there'd be no traveling through space?

Never mind. Don't go there. Another topic. I see now what you are saying. Time for me to re-read. Thank you.
vivian maxine
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### Re: Can a vacuum have a speed?

Hi Vivian,

If you where in a Super Sonic passenger jet moving along at 50% faster than the speed of sound, then the sealed inside of the Jet contains air and sound will move through that internal air at the normal speed of sound (767 MPH). That's the Tube ralfcis is suggesting, it's sealed off.

So, if that tube is a Spaceship, moving at say 50% the Speed of Light, the sound inside would pretty much still travel inside at the speed of sound.

But...

If you set off a flash of light in the center of the cabin, it's a different story. The light will hit the back wall before it reaches the front wall because the Space-Time medium inside is the same as outside the ship. The back wall of the cabin is coming towards the flash and will meet the flash sooner than if the ship was standing still. Likewise the flash will have to catch up with the front wall as it is moving away from the original location of the flash.
But, when that flash to the front and back bounce and return to the center, everything get reversed and the flash will arrive back at the center from both ends at the same time.

Just keep in mind, the center where the flash started and the center where it bounced back to are the physical center of the ship, but both centers are not the same place in Space-Time.

This might help:

Imagine you are inside a big long box, sitting on a shelf hooked to a wall. There is no floor but rather the floor is just a tiny bit above the surface of a very calm lake. The box is moving pretty slow, like only half the speed of a wave in the water if there was a wave. Now, sitting on that shelf, in the center of the box, drop a rock in the water below and watch the waves.

The waves will reach the back of the box before they reach the front of the box. But, because the box is so close to the water, the waves bounce off the back and front and return to the center of the box, at the same time. But you might also notice that the original spot where the rock hit the water in now much further towards the rear because the box is moving forward rather slowly. This water medium below the box represents Space-Time and is independent from the box. But waves of information follow the same rules and speed limits of the medium.

If I had the time, I would make a video of this and it would be much easier to see how this all works.

Hope this helped and didn't muddy up the water.. lol.

Regards,
Dave :^)

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### Re: Can a vacuum have a speed?

ralfcis » 10 Mar 2017, 19:21 wrote:Ok so if you have particles popping in and out of existence from a vacuum in a tube and you could plot the distance between where the particles pop out then pop back, ...

Ralf, "particles popping in and out of existence" is not part of SR, but of the quantum regime. While you still have difficulties comprehending SR, don't try to go there...

People tend to forget that SR do not even have photons, just spacetime, light waves, light fronts and little "billiard balls" with so little mass that they do not distort spacetime. We know that it is only an approximation of reality, but we need to understand it to possibly comprehend the rest.

And please do not complain that this is a vague answer - you are frankly not ready for a more detailed answer ...

BurtJordaan
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### Re: Can a vacuum have a speed?

Dave, you have air inside the tube. I thought it was a vacuum. There is no air in a vacuum. Or has my little bit of eighth grade physics gone awry?

Ralfcis said: But if the train was a vacuum tube with closed ends, and you could somehow create slowed light in a vacuum, would the speed of the train boost the speed of that slowed light in a moving vacuum relative to a stationary observer? Is the speed of the vacuum in side the tube the same as the speed of the vacuum outside the tube?

Which gets me to my next question. Things (concrete things) will, I think, move in a vacuum - more slowly but will move. Am I right so far? Question: Can light - or a magnetic wave - move in a vacuum? Or does " the impossibility of slowed light in a vacuum" mean it can not?

I also have a question about something you posted above. But I'm holding that for now. This gets interesting and I hope some light is beginning to shine on it for me.

Ralfcis, I like the way you are not afraid to say such as "as seen by an outside observer" or "relative to a stationary observer". I have tried often to pin that down in my understanding of relativity but never succeeded in getting a confirmation.
vivian maxine
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### Re: Can a vacuum have a speed?

You have to go to relativity court to get a confirmation and judging by Jorrie's responses, there's no such thing as relativity court.
ralfcis
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### Re: Can a vacuum have a speed?

Viv, Dave was right up to here:

Dave_Oblad » 10 Mar 2017, 19:58 wrote:Hi Vivian,

If you where in a Super Sonic passenger jet moving along at 50% faster than the speed of sound, then the sealed inside of the Jet contains air and sound will move through that internal air at the normal speed of sound (767 MPH). That's the Tube ralfcis is suggesting, it's sealed off.

So, if that tube is a Spaceship, moving at say 50% the Speed of Light, the sound inside would pretty much still travel inside at the speed of sound.

Because Dave pretends that light works the same as sound, the rest of his post is scientifically very questionable, to say the least. You will be well advised to ignore it, because it is guaranteed to "muddy the waters" for you. ;)

I think you have already read the threads where Dave's premises were falsified, so we are not going there again.

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### Re: Can a vacuum have a speed?

I am reading the entire thread over and over. It is rare for me to find anything in physics that I can understand. Much of it is strange vocabulary which doesn't seem to merit explanation. So, I just let it go. But this is beginning to make sense, thanks to those who know physics.

A friend just raised a question. A vacuum, to our earthly minds, has to be sealed and all air removed. Almost all of it anyway. Outer space is a vacuum but, so far as we know now, it is not sealed. I think here is where we go into the story of air. Or into the mystery of "what is out there?"
vivian maxine
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### Re: Can a vacuum have a speed?

Viv, yes, no vacuum is the "perfect vacuum", but we can make it close enough for all practical purposes.

Also, professionals in every field have a "trade terminology" that all (all most) of them in the field understand. And in many cases the terms mean slightly different things, depending on the context of what is discussed. This makes it very difficult for newcomers to the trade to understand exactly what is meant. Or for newcomers to convey to the pro's what exactly they mean when asking questions.

I guess this is just the nature of the beast.

BurtJordaan
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### Re: Can a vacuum have a speed?

This is a nonsensical question. Vacuum is not something that can have a speed.

As far as the relative speed of light in a relatively moving glass is concerned, you just need the relativistic addition formula,

which is always < c.

Ok as we go to an even more rarified medium, from glass to air to helium to hydrogen to partial vacuum, all the while getting closer and closer to the permittivity and permeability values of space, at what point is the contained medium no longer able to have a speed?
ralfcis
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### Re: Can a vacuum have a speed?

BurtJordaan » March 10th, 2017, 3:05 pm wrote:Viv, yes, no vacuum is the "perfect vacuum", but we can make it close enough for all practical purposes.

Also, professionals in every field have a "trade terminology" that all (all most) of them in the field understand. And in many cases the terms mean slightly different things, depending on the context of what is discussed. This makes it very difficult for newcomers to the trade to understand exactly what is meant. Or for newcomers to convey to the pro's what exactly they mean when asking questions.

I guess this is just the nature of the beast.

Most of the science books that I have have glossaries in the back. Of course, most of the science books that I have were written for the likes of me. So glossaries are great. That said, have you ever bought a technical book and found that it has no index? Not just science books but many types. That should be a capital crime. :-)

Back on topic. Ralfcis, is this speed a medium is not able to have its own speed or the speed of the carrier it is in (like the sealed tube)?
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