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Physics, Astronomy & Cosmology / Re: What would happen to the Solar System's gravitational connections if ....?

« on: 14/07/2022 19:18:00 »

while, on a occasion, a comet does crash into the Sun, the newly formed Black hole would be an extremely small target to hit.

So the Sun turning into a BH would affect the orbit of a comet but not (as @Halc  says) that of the planets?

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Physics, Astronomy & Cosmology / Re: What would happen to the Solar System's gravitational connections if ....?

« on: 11/07/2022 17:03:04 »

Nothing of course. You seem to know this already.  The orbits are determined by acceleration=GM/r² and period=√(4π²r³/GM) and none of those values are changing in your scenario

No ,I was genuinely unsure.On account of an ongoing discussion over at scienceforums.net where Markus Hanke is being quizzed by MigL and now myself about BHs  EHs and causality

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Physics, Astronomy & Cosmology / What would happen to the Solar System's gravitational connections if ....?

« on: 11/07/2022 14:19:13 »

What if the Sun became a black hole almost  instantaneously?

Suppose  we were living in a Solar System where the Sun was much smaller but equally  massive.

The planets were orbiting  this Sun in almost the same way  as in ours   and then ,one day the Sun tipped over into  a black hole for whatever reason ( not including the arrival of a foreign body but presumably  something that caused its radius to shrink )

In that scenario what would happen to    the orbits of the planets?

Would things continue as if nothing had  changed in that regard?

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Physics, Astronomy & Cosmology / Re: What is a black hole made of?

« on: 28/06/2022 14:54:20 »

At this point, it really doesn't matter what the black hole formed from, because that is not detectable from outside

Have heard that said before.Would there be no way to guess (correctly) what a black hole is formed from ...and any way to know if we were correct(and make use of the seemingly correct  knowledge)?

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Physics, Astronomy & Cosmology / Re: What is a black hole made of?

« on: 28/06/2022 02:01:10 »

I have read that black holes might be viewed not as objects at all but  as extreme spacetime  curvature 

Is that correct or have I perhaps  misconstrued?

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Physics, Astronomy & Cosmology / Re: How would we know whether space,time or spacetime were continuous or discrete?

« on: 26/06/2022 14:50:22 »

The idea of quantisation of photon energy arose from a need to explain observations and is frequently misinterpreted.

Our best explanatory model is that charge is indeed quantised, as are the electron energy levels in any given atom, but a different atom can have arbitrarily different energy levels (which is why we can distinguish them spectroscopically) so "energy" is a continuum.

Thus there is no a priori reason to suspect that "space" or "time" is quantised.

I remembered  your post just now and want to ask you how it can be known that the energy levels can take any value?

How is it required that  some discreteness  is not also embedded into that seeming continuum?

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Physics, Astronomy & Cosmology / Re: Does The Gravity Of A Black Hole Travel Faster Than The Speed Of Light ?

« on: 21/06/2022 01:22:07 »

Perhaps this might be relevant to that video

https://en.m.wikipedia.org/wiki/Jean-Pierre_Petit

"In the 1990s, he stated on various French TV shows that some of his main scientific ideas were directly from his analysis of the Ummo case and documents, questioning their terrestrial origin.[citation needed] He said in 2018 that he experienced personal contacts with unidentified entities that may or not be related to the Ummo case, but that he believes are aliens.[5][non-primary source needed]

The Ummo affair is generally believed to have been a sophisticated hoax elaborated by a person without technical knowledge.[6

Have we been blessed with a visitation of emissaries from the stars?

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Physics, Astronomy & Cosmology / Re: How would we know whether space,time or spacetime were continuous or discrete?

« on: 18/06/2022 20:25:54 »

Come to think of it, Heisenberg pretty well contradicts the idea of granular spacetime. As you decrease the uncertainty of your position measurement, so you increase the indeterminacy of your momentum. If both space and time were granular there would only be a finite number of discrete values of both, so indeterminacy would be limited and we'd be back to the impossible orbiting electron model of an atom.

I hope you are right as that would put my question to bed.
It is nice to occasionally  remove another misunderstanding from one's repertoire.

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Physics, Astronomy & Cosmology / Re: Does The Gravity Of A Black Hole Travel Faster Than The Speed Of Light ?

« on: 14/06/2022 18:30:05 »

Changes to masses inside a black hole emit gravitational waves that cannot leave the black hole for the same reason light cannot

What ,then, is the effect of changes to the distribution of mass inside a BH?  Anything?   Do we know?

A change in the distribution of mass would be a form of mass itself wouldn't it?

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Physics, Astronomy & Cosmology / Re: How would we know whether space,time or spacetime were continuous or discrete?

« on: 12/06/2022 17:52:36 »

. I suspect geordief likes these continued discussions

Yes he does.It takes me a lot of effort to follow the replies ,though after my  question has been answered in the main.

And I may no longer be able to contribute  but  I follow as far as I can.

I find the world as built up of "events" rather than objects /systems evolving in time very interesting  and find the former to be equally acceptable (more so actually) on an intuitive level.

Apparently spacetime is a model  designed to be just a coordinate system (a local one) without any objects  necessarily occupying  any particular location  but I have also wondered if  those  locations could be populated by  real events.(ie if  the real events  could define the location in spacetime)

Seems ,maybe it can be one or the other but not both at the same time?

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Physics, Astronomy & Cosmology / Re: How would we know whether space,time or spacetime were continuous or discrete?

« on: 11/06/2022 20:26:05 »

(as an aside  ,does the thinking process have to follow the same laws and are our minds forbidden to imagine possibilities  at some deep physical level no matter how unrestrained our imagination can appear to us? Even imagination would be tethered?)

I think about this question from time to time.  It is quite interesting. 

Yes, there is a lot of evidence that imagination is tethered/correlated to a chemical process in the brain, but it is only said to be a correlation.  They are not necessarily interchangeable entities.  For example, the image of an orange in my brain is only known to be correlated to a process in my brain; it is not known to be the same thing as the process in my brain.  This is at least how science is dealing with the relationship between body and mind. 

Anyways, this means that there is no telling what thoughts, theories or answers we may think of.  Our imagination would be limited only by how many possible processes in the brain there can be. 



   

I can see why the mechanisms whereby the brain processes reality (which ,to my mind includes all kinds of abstract and not simply functional processes) ..I can see how fascinating and absorbing that must be to anyone involved.

But it was really just the "limited" part that I was addressing.

You seem to have given me an answer. There is indeed a limit ,even if for nearly all practical purposes we might say that that limit need not concern us (unless in the future we develop mental prosthetics and our brains are able to directly tap into the workings of artificially intelligent machines)

Even there the limit still applies even if only in theory.

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Physics, Astronomy & Cosmology / How would we know whether space,time or spacetime were continuous or discrete?

« on: 11/06/2022 11:30:59 »

I understand that we have no answer as yet and my intimation  is that we may never know (although "we" may build a satisfactory model based on either supposition.)

In the meantime, what indications are there that one of these two paths might eventually bear fruit?

Is it all going to boil down    to some clever person devising an experiment that more or less rules out one of the options or  can some possibilities already be ruled out on the basis of existing understandings?

Suppose ,say one was investigating a possible discreteness, at what level might that be conjectured to occur -and would some mechanism be required to cause this or would  we reach the end of the chain of causality at that point?

(as an aside  ,does the thinking process have to follow the same laws and are our minds forbidden to imagine possibilities  at some deep physical level no matter how unrestrained our imagination can appear to us? Even imagination would be tethered?)

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Physics, Astronomy & Cosmology / Re: What are the properties of space?

« on: 10/06/2022 01:05:40 »

What is it that makes stuff separate from itself? (rarified?)

Why is it not happy just being together with itself,with no distance between its constituent parts?

Are all the separate bits of stuff  forever connected or forever  separate? (both?neither?)

Is that a very poor philosophical question as well as a poor scientific question?

Do we just start with what we observe and not try to second guess  what is out there and in here?

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Physics, Astronomy & Cosmology / Re: Does The Universe Spin ?

« on: 05/06/2022 17:03:33 »

One could say that a 'thing' is something to which you can point, and also be able to point to not-the-thing.
So I can point to both an apple and the table on which it rests, the latter qualifying as not-apple.

Yes, that's better.

Language is a source of a lot of misguided intuition about such topics. It leads to assumptions for which there isn't any actual evidence

Oh,yes.

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Physics, Astronomy & Cosmology / Re: Does The Universe Spin ?

« on: 05/06/2022 13:31:43 »

Why is the Universe  not a thing ? isn't it every-thing ?  which is also a thing ?

Everything spins, but the universe isn't a thing. An object without a bounded size cannot meaningfully spin.

Ewe spin me right round quickly,
tight round, getting dizzy,
ralph a one pound ground round mound

Spin in relation to what?

Spin is absolute, and need not be in relation to any particular frame, although something's angular momentum is at least relative to an axis, but angular moment and spin (RPM say) are different things.

I think the universe  is only a "thing" if you can point to it  some way.
I can't see how we could do that even in principle.

Of course we have the word in the dictionary and  it can be used  in the system of language that we use

So ,in that sense it exists(semanticaly) but not in the sense that you seem to be asking

If  you were to ask about the observable universe I would be interested to know if there was any detectable spin ,but I am not sure what frame of reference could be chosen even then that might give an answer that would  apply to the observable universe as a whole.

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Physics, Astronomy & Cosmology / Re: Does "empty space" push things away and gravity is lack of this push energy?

« on: 05/06/2022 12:56:21 »

doesn't matter too much if gravity was really "caused" by something else.   "Cause" is a very subjective term anyway

I like that.It is nice to maybe dispense with another misconception.

There is ,I think a misconception that we may be well placed to understand everything

Every day mysteries do no harm.

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Physics, Astronomy & Cosmology / Re: Does "empty space" push things away and gravity is lack of this push energy?

« on: 05/06/2022 10:50:14 »

Yes ,I thought it was a good question too and had no idea it might have been discussed in previous generations.

Is "empty space" ,though an undefined idea and do we fall back on the measured intervals between objects as  more reliable points of reference?

So we have objects  with measured distances between them dancing with each other and these measured distances ,when set out in geometrical form seem to observe a behaviour that corresponds to what we see as the action of gravity in our world and also at the edges  of the observable universe.

Could that be an interpretation ?

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Physics, Astronomy & Cosmology / Re: Could neutrinos pass through a black hole?

« on: 12/02/2022 13:25:54 »

Perhaps a related question - would hypothetical gravitons be absorbed by a black hole?
- If a black hole is (say) 10km across
- And the gravitational waves have a wavelength of (say) 30,000km?

I expect that wavefunction of the gravitons allow you to calculate the probability that a particular graviton is found at a particular point in space
- There is a finite probability that an individual graviton will impact the event horizon of the black hole
- Since there are so many gravitons in a gravitational wave, some of them will impact the event horizon, and be absorbed.

The same argument applies to photons in an electromagnetic wave with a wavelength of 30,000km.

How might we (in theory) detect that a graviton  had interacted with the  actual singularity** of a black hole?

Could the probability of such an occurrence  exceed by very many orders the lifetime of the universe and so be considered impossible?

** are singularities mathematical objects without a physical counterpart?

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Physics, Astronomy & Cosmology / Re: Could neutrinos pass through a black hole?

« on: 12/02/2022 04:01:15 »

Nothing escapes a black hole, which is not a star, nor even a location in coordinate space.

(with usual apologies  in advance for probable misunderstanding) How then can we say that there is expected to be a Black Hole  at the centre of every Galaxy?

Is there not a frame of reference involved in such a description?

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Physics, Astronomy & Cosmology / Re: If space-time can curve near a black hole, can we drag + move it?

« on: 04/02/2022 01:03:46 »

Hi.

   Could someone clarify how these things work?   Whenever the posts start of with  "Donald presented this...."  or   "Donald wrote in to ask this.....",    then   we're never going to get any interactivity with Donald are we?   
   So am I right that if I asked Donald to clarify a few details, then I'd be wasting my time?

    Also when people write a reply, such as Origin has just done,  will Donald ever see it, hear it or care about the reply in the slightest?   To phrase the question another way:   What is the point of replying to these things?   Would Origin have done just as well to shout his last reply down the street on a quiet night?

Best Wishes

That  was very funny
(I am as baffled as you are)