Black-holes, gravity, and vacuum?

[jajrussel]

Is it okay for me to assume that the interior of a black-hole is not a vacuum?

Is it okay for me to assume that if gravity is detected within a given volume of space that, that volume of space is not a vacuum?

Is it okay for me to assume that whenever someone mentions something moving faster than light that their statement must mean a vacuum is implied?

The third question is based upon a reply in another thread that stated nothing ever moves faster than light. Yet I had recently watched a video that seems to imply that in certain conditions well, yes somethings can move faster than light. I can only assume that the person that made the statement, assumed that when the question was asked, that the "nothing ever moves faster than light" statement should simply disqualify the question in part. This can get confusing...

The first two questions were kind of generated by my thinking about the third question. Sometimes when a Pat answer is given conclusively I feel disappointed, it doesn't seem to matter if the answer is posed to me  or someone else. Is this video wrong?

Another good video

 

Edited November 1, 2018 by jajrussel

[Strange]

4 hours ago, jajrussel said:

Is it okay for me to assume that the interior of a black-hole is not a vacuum?

Well, we really don't know. According to GR anything that falls into the black hole rapidly falls into the singularity at the centre. So, if the black hole were "active" (lots of material falling into it) then the inside would not be a vacuum - it would contain the stuff that had fallen in, on its way to the centre. On the other hand, if it reasonably isolated so nothing is falling in, then the inside will be a vacuum.

On the other (third?) hand, string theory describes black holes as being full of "fuzz".

4 hours ago, jajrussel said:

Is it okay for me to assume that if gravity is detected within a given volume of space that, that volume of space is not a vacuum?

One challenge here is what you mean by "vacuum". In intergalactic space, there are just a few particles per cubic metre. That is a much better vacuum than we can make on Earth.

But, basically, the presence of gravity is independent of whether the space is empty or not.

If there is gravity in a vacuum then it would, perhaps obviously, be due to the presence of mass outside the area that was a vacuum. (Note that gravity has an infinite range so even in the vacuum of space between galaxies, there will be gravity from those galaxies.)

5 hours ago, jajrussel said:

The third question is based upon a reply in another thread that stated nothing ever moves faster than light. Yet I had recently watched a video that seems to imply that in certain conditions well, yes somethings can move faster than light.

I guess from the title of the video, this is about Cerenkov radiation (can't watch videos). In that case, it is produced when a particle moves through a medium (air, water, glass) faster than the speed of light in that medium (which will always be slower than the speed of light in a vacuum). So the "speed of light" limit is actually the "speed of light in a vacuum" limit.

(Haven't been able to watch your 2nd video, so not sure what that is about ...)

[Carrock]

4 minutes ago, Strange said:

(Haven't been able to watch your 2nd video, so not sure what that is about ...)

I watched part of the second video.

A claim was that you can send information FTL using quantum entanglement (false) but you can't send a message FTL (true).

The sort of video that's worse than a waste of time.

[jajrussel]

22 minutes ago, Carrock said:

I watched part of the second video.

A claim was that you can send information FTL using quantum entanglement (false) but you can't send a message FTL (true).

The sort of video that's worse than a waste of time.

Really? I apparently need to watch the video again. I missed the part you describe. I have always found Cern videos to be decent videos. Perhaps the link was highjacked on the way to your device?

Or, perhaps I should have just watched half the video then made an assumption?

Edited November 1, 2018 by jajrussel

[Carrock]

At 5min32sec "information in quantum mechanics can travel faster than light" etc

Edited November 1, 2018 by Carrock
Clarified time ref

[koti]

7 minutes ago, Carrock said:

At 5min32sec "information in quantum mechanics can travel faster than light" etc

Someone from Fermilab should be made aware what Doctor Don Lincoln is telling people on youtube. Besides this obviously false statement the whole video is very poor. Why is such crap on Fermilab's channel is worrying.

[jajrussel]

We seem to be entering the Ludacrous Zone. I give up... But you are right it is Fermilab...

Okay maybe I haven't given up. The concept of apply action at a distance sounds ludicrous, and yes he mentions it, but at about 5:40 he explains why the concept needs work. I find it hard to believe that you watched the video and came away thinking he championed the concept. It the concept that I have trouble accepting, and believe me if I thought he championed the concept. I would at the minimum be questioning the statement if he made it, by trying to understand why he made it rather then inferring that the whole vid is crap just because he seemed to be saying something I don't understand.

There are vids that actually do make the statement rather convincingly with intent. I don't believe that anywhere in this video that he implied that entering the Startrek zone was anything but ludicrous, but yes under certain conditions things do move faster than light and he gave the perfect example with Cerenkov radiation.

Now I give up...

Edited November 1, 2018 by jajrussel
I really really hate these so-called smart keyboards that have been taught that u is a word.

[Carrock]

Luckily I left this topic on my browser and refreshed it or I'd never have seen your edit....

Hard to analyse a video compared to text...

 

Around 5m 20s '"Spooky action at a distance" says that...'

At 5min32sec "information in quantum mechanics can travel faster than light" etc

followed shortly by

'Nobody understands this, but it's well established and it's a true effect.'

 

"Spooky action at a distance" is well understood mathematically (not by Doctor Don Lincoln) though there is disagreement about its implications, much like 'observing' in quantum mechanics.

Action at a distance does not involve the superluminal transfer of information.

'Information' as used by Doctor Don Lincoln has an unspecified different meaning from the normal meaning as in 'information cannot move faster than light.'

 

When I see a false statement justified by 'Nobody understands this' (i.e. the author doesn't understand it) I don't see the point in watching the rest of a video where nothing I don't know already can be trusted.

 

Doctor Don Lincoln does hint that his 'information' is different but anyone trying to learn from this video will likely conclude that physics is really difficult and should be left to clever people like him.

 

[swansont]

22 hours ago, jajrussel said:

Is it okay for me to assume that if gravity is detected within a given volume of space that, that volume of space is not a vacuum?

No.

The kind of clocks I have built require both a vacuum* and the presence of gravity in that vacuum in order to work.

 

*As Strange has observed, one needs to specify what is meant by vacuum. I'm using a common lab definition: a region at a pressure lower than atmosphere. (pressure is of order 10^-10 torr, where atmosphere is 760 torr, so better than a trillionth of atmosphere)

[Raider5678]

17 hours ago, Strange said:

But, basically, the presence of gravity is independent of whether the space is empty or not.

1

Would this mean if there was no mass there'd still be gravity or just that no matter where you go if there is so much as a single particle somewhere there is gravity?

[Strange]

24 minutes ago, Raider5678 said:

Would this mean if there was no mass there'd still be gravity or just that no matter where you go if there is so much as a single particle somewhere there is gravity?

If there was no mass (or energy) anywhere then there would be no gravity. But the question was (as I understood it) about an area where there was a vacuum, within the universe. In that case, there would be gravity, even in the vacuum, because of the presence of mass elsewhere.

[Raider5678]

Just now, Strange said:

If there was no mass (or energy) anywhere then there would be no gravity. But the question was (as I understood it) about an area where there was a vacuum, within the universe. In that case, there would be gravity, even in the vacuum, because of the presence of mass elsewhere.

Alright.

[jajrussel]

23 hours ago, swansont said:

No.

The kind of clocks I have built require both a vacuum* and the presence of gravity in that vacuum in order to work.

 

*As Strange has observed, one needs to specify what is meant by vacuum. I'm using a common lab definition: a region at a pressure lower than atmosphere. (pressure is of order 10^-10 torr, where atmosphere is 760 torr, so better than a trillionth of atmosphere)

Okay,  so if I had said perfect vacuum would that have been enough, because my thought was that by simply introducing Mass to a vacuum that that Mass would interfere with any other Mass introduced. I'm gonna guess that a perfect vacuum has been defined, so I would have still had to gave been more specific.

Where can I read about these clocks? I'm wondering? If they require a specific atmosphere to be accurate could thethe effect of various places on time be simulated by by simulating the atmosphere of the place? Hmm, I'm guessing you would still have to account for the normal gravity of that place... But, if the clock was moved to a place that might simulate that places gravity then it would effect the clock because the pressure required for the clocks accuracy would change in the moving. I'm just guessing here, cause I am clueless.

Edited November 3, 2018 by jajrussel

[swansont]

6 hours ago, jajrussel said:

Okay,  so if I had said perfect vacuum would that have been enough, because my thought was that by simply introducing Mass to a vacuum that that Mass would interfere with any other Mass introduced. I'm gonna guess that a perfect vacuum has been defined, so I would have still had to gave been more specific.

Where can I read about these clocks? I'm wondering? If they require a specific atmosphere to be accurate could thethe effect of various places on time be simulated by by simulating the atmosphere of the place? Hmm, I'm guessing you would still have to account for the normal gravity of that place... But, if the clock was moved to a place that might simulate that places gravity then it would effect the clock because the pressure required for the clocks accuracy would change in the moving. I'm just guessing here, cause I am clueless.

You can look for papers on atomic fountain clocks.

The vacuum is to reduce scattering of the atoms from background gas, and allow you to collect the desired atoms. The actual value if g is irrelevant - the requirement is to have gravity present so when you toss the cloud of atoms up that it comes back down.

The salient point being that gravity is not affected by the pressure. 

If gravity didn't work in a vacuum we wouldn't be able to orbit the sun.