I've just finished reading the book "White Holes" by Carlo Rovelli, and
it's left me seriously puzzled. Is anyone else familiar with this book?

From all the evidence available to me, Rovelli appears to be recognised
as a respectable physicist, not at all the sort of person who makes
u-tube videos about rail guns. The book, on the other hand, is written
in a style that one would expect from a deluded crackpot. His arguments
are partly from analogy, and partly from the numerous references to
Dante's /Divine Comedy/. I'll concede that one shouldn't expect
scientific rigour in a popular science book, but Rovelli falls over
backwards to avoid any concession to logical reasoning.

For those that haven't heard of them, white holes are the opposite of
black holes. Matter than passes the event horizon of a black hole can't
return, because of the extreme gravity. But matter can't enter a white
hole, it can only exit. From this one would expect a white hole to
radiate lots of energy. But no, Rovelli seems to say that from the
outside a white hole would look just like a black hole. (He gives no
justification for this assertion.) White holes have not yet been
observed, but given the time distortions around a black hole singularity
one might expect them to appear only after an infinite amount of time
has passed. That last sentence is my comment, not Rovelli's.

His starting point is that the equations of General Relativity work
equally well with time running forwards or backwards. So far, that's in
agreement with mainstream thinking. But from this he creates a scenario
where matter that falls into a black hole can get close to the
singularity, in a region where General Relativity does not hold, and
then be time-reversed and bounce back out as the product of a white hole.

[My immediate reaction: if a time-reversed object travels out of the
hole, then those of us who live forward in time will see it as falling
into the hole. But maybe I've missed his point.]

What is the reason such a bounce is possible? Well, Dante explained
that. You can travel down to the innermost part of Hell, and there you
will find ... not a singularity, but a way to exit from Hell. QED.

Have I missed seeing something important?

--
Peter Moylan http://www.pmoylan.org
Newcastle, NSW

Le 04/04/2024 à 06:17, Peter Moylan a écrit :
>
> For those that haven't heard of them, white holes are the opposite of
> black holes. Matter than passes the event horizon of a black hole can't
> return, because of the extreme gravity. But matter can't enter a white
> hole, it can only exit. From this one would expect a white hole to
> radiate lots of energy. But no, Rovelli seems to say that from the
> outside a white hole would look just like a black hole. (He gives no
> justification for this assertion.) [...]

Isn't the clue in the name, /white/ holes, which marks them as the
opposite of... holes of colour?

Peter Moylan wrote:

> I've just finished reading the book "White Holes" by Carlo Rovelli, and
> it's left me seriously puzzled. Is anyone else familiar with this book?

> From all the evidence available to me, Rovelli appears to be recognised
> as a respectable physicist, not at all the sort of person who makes
> u-tube videos about rail guns. The book, on the other hand, is written
> in a style that one would expect from a deluded crackpot. His arguments
> are partly from analogy, and partly from the numerous references to
> Dante's /Divine Comedy/. I'll concede that one shouldn't expect
> scientific rigour in a popular science book, but Rovelli falls over
> backwards to avoid any concession to logical reasoning.

> For those that haven't heard of them, white holes are the opposite of
> black holes. Matter than passes the event horizon of a black hole can't
> return, because of the extreme gravity. But matter can't enter a white
> hole, it can only exit. From this one would expect a white hole to
> radiate lots of energy. But no, Rovelli seems to say that from the
> outside a white hole would look just like a black hole. (He gives no
> justification for this assertion.) White holes have not yet been
> observed, but given the time distortions around a black hole singularity
> one might expect them to appear only after an infinite amount of time
> has passed. That last sentence is my comment, not Rovelli's.

> His starting point is that the equations of General Relativity work
> equally well with time running forwards or backwards. So far, that's in
> agreement with mainstream thinking. But from this he creates a scenario
> where matter that falls into a black hole can get close to the
> singularity, in a region where General Relativity does not hold, and
> then be time-reversed and bounce back out as the product of a white hole.

> [My immediate reaction: if a time-reversed object travels out of the
> hole, then those of us who live forward in time will see it as falling
> into the hole. But maybe I've missed his point.]

> What is the reason such a bounce is possible? Well, Dante explained
> that. You can travel down to the innermost part of Hell, and there you
> will find ... not a singularity, but a way to exit from Hell. QED.

> Have I missed seeing something important?

Gravitons!

They are the basic to quantum entanglement.
In a quantum entangled world, one can assume that gravitons fill the void
called space, with instantaneous communication from any point to the other.
The ancient "action at a distance" principle for gravity remains valid!!!!!

It is thus not a question of singularities like wormholes leading from
one universe to another parallel universe. Or some point in this universe,
and then back again by the same wormhole to the same place, for
futuristic interstellar transport, as hinted by modern science fiction.

Mass transfer can be instantaneous with the anticipated transformation
of matter to gravitons, for instantaneous "travel"
to any desired point along the spacetime geodesic.

On the other hand, wormholes may be created artificially, like black holes
and could be directed to some part of the universe. Our present lack of
theoretical insight is somewhat lacking maybe, but then who knows when the
next Einstein will be born!

Had white holes actually existed, perhaps they would have been seen
had their radiation been different from normal stars. However, maybe
evey star is a potential white hole! Who knows! There are so many
black holes, posing as dark matter. Assuming they are already connected
by natural wormholes, it is only a question of time before these tunnels
are used for space travel.

It is charming to bring in an ancient poet to a modern physics discussion.
What wonderful insights great poets have!

bt

On 04/04/24 17:24, Hibou wrote:
> Le 04/04/2024 à 06:17, Peter Moylan a écrit :
>>
>> For those that haven't heard of them, white holes are the opposite
>> of black holes. Matter than passes the event horizon of a black
>> hole can't return, because of the extreme gravity. But matter can't
>> enter a white hole, it can only exit. From this one would expect a
>> white hole to radiate lots of energy. But no, Rovelli seems to say
>> that from the outside a white hole would look just like a black
>> hole. (He gives no justification for this assertion.) [...]
>
> Isn't the clue in the name, /white/ holes, which marks them as the
> opposite of... holes of colour?

This is starting to border on a pornographic discussion. I've been told
that a literal translation of "black hole" into Russian gives an obscene
term. I've also been told that this is rubbish, a tale that somebody
made up.

The suggested property of white holes seems to require a new variety of
gravity, one that produces a repulsive force. This is not entirely
unthinkable. In the area of electrical forces, it has been shown that
anti-electrons and anti-protons really do exist. (The jury is still out
on magnetic monopoles, but if they exist we would expect two kinds.) But
I have no idea as to whether antigravity is consistent with General
Relativity.

--
Peter Moylan http://www.pmoylan.org
Newcastle, NSW

On 04/04/24 17:37, bertietaylor wrote:
> Peter Moylan wrote:

>> His starting point is that the equations of General Relativity
>> work equally well with time running forwards or backwards. So far,
>> that's in agreement with mainstream thinking. But from this he
>> creates a scenario where matter that falls into a black hole can
>> get close to the singularity, in a region where General Relativity
>> does not hold, and then be time-reversed and bounce back out as the
>> product of a white hole.
>
>> [My immediate reaction: if a time-reversed object travels out of
>> the hole, then those of us who live forward in time will see it as
>> falling into the hole. But maybe I've missed his point.]
>
>> What is the reason such a bounce is possible? Well, Dante
>> explained that. You can travel down to the innermost part of Hell,
>> and there you will find ... not a singularity, but a way to exit
>> from Hell. QED.
>
>> Have I missed seeing something important?
>
> Gravitons!
>
> They are the basic to quantum entanglement. In a quantum entangled
> world, one can assume that gravitons fill the void called space, with
> instantaneous communication from any point to the other. The ancient
> "action at a distance" principle for gravity remains valid!!!!!

Traditional action at a distance has a time delay. For example, if an
electron suddenly came into existence, the resulting change in the
electric field would propagate outwards at the speed of light. The
concept of quantum entanglement is upsetting because it suggests that
information can be communicated at greater than the speed of light.
That, in turn, says that Special Relativity is wrong. Which brings a
whole lot of theory tumbling down ... is Arindam reading this?

Long-distance communication via gravity waves does assume a time delay,
so it's not a quantum entanglement effect. As I understand it, quantum
entanglement does not allow any information transfer, and that's how a
paradox is avoided.

> It is charming to bring in an ancient poet to a modern physics
> discussion. What wonderful insights great poets have!

Charming? From an artistic viewpoint, yes. But I reject the suggestion
that Dante's opinions had any relationship to reality.

--
Peter Moylan http://www.pmoylan.org
Newcastle, NSW

bertietaylor@myyahoo.com (bertietaylor) wrote or quoted:
>Gravitons!
>They are the basic to quantum entanglement.

When a system is made up of multiple subsystems,
it's considered "entangled" if you can't just write its state as
a simple product of the states from those individual subsystems.
This has no specific connection to gravitons.

Hibou wrote:

> Le 04/04/2024 à 06:17, Peter Moylan a écrit :
>>
>> For those that haven't heard of them, white holes are the opposite of
>> black holes. Matter than passes the event horizon of a black hole can't
>> return, because of the extreme gravity. But matter can't enter a white
>> hole, it can only exit. From this one would expect a white hole to
>> radiate lots of energy. But no, Rovelli seems to say that from the
>> outside a white hole would look just like a black hole. (He gives no
>> justification for this assertion.) [...]

> Isn't the clue in the name, /white/ holes, which marks them as the
> opposite of... holes of colour?

Black Labs matter! - says black Labrador.
Don't you start. - says white Labrador.

All Labs are black in the dark.
ditto for holes.

On 2024-04-04 12:12:51 +0000, Peter Moylan said:

> On 04/04/24 17:37, bertietaylor wrote:
>> Peter Moylan wrote:
>
>>> His starting point is that the equations of General Relativity
>>> work equally well with time running forwards or backwards. So far,
>>> that's in agreement with mainstream thinking. But from this he
>>> creates a scenario where matter that falls into a black hole can
>>> get close to the singularity, in a region where General Relativity
>>> does not hold, and then be time-reversed and bounce back out as the
>>> product of a white hole.
>>
>>> [My immediate reaction: if a time-reversed object travels out of
>>> the hole, then those of us who live forward in time will see it as
>>> falling into the hole. But maybe I've missed his point.]
>>
>>> What is the reason such a bounce is possible? Well, Dante
>>> explained that. You can travel down to the innermost part of Hell,
>>> and there you will find ... not a singularity, but a way to exit
>>> from Hell. QED.
>>
>>> Have I missed seeing something important?
>>
>> Gravitons!
>>
>> They are the basic to quantum entanglement. In a quantum entangled
>> world, one can assume that gravitons fill the void called space, with
>> instantaneous communication from any point to the other. The ancient
>> "action at a distance" principle for gravity remains valid!!!!!
>
> Traditional action at a distance has a time delay. For example, if an
> electron suddenly came into existence, the resulting change in the
> electric field would propagate outwards at the speed of light. The
> concept of quantum entanglement is upsetting because it suggests that
> information can be communicated at greater than the speed of light.
> That, in turn, says that Special Relativity is wrong. Which brings a
> whole lot of theory tumbling down ... is Arindam reading this?

I think Arindam gave up on this group long ago because he couldn't find
anyone to accept his claptrap. He's recently become quite noticeable at
sci.physics.relativity. He doesn't convince the real scentists there
either, but there are lots of crackpots who may take him seriously.
>
> Long-distance communication via gravity waves does assume a time delay,
> so it's not a quantum entanglement effect. As I understand it, quantum
> entanglement does not allow any information transfer, and that's how a
> paradox is avoided.
>
>> It is charming to bring in an ancient poet to a modern physics
>> discussion. What wonderful insights great poets have!
>
> Charming? From an artistic viewpoint, yes. But I reject the suggestion
> that Dante's opinions had any relationship to reality.

--
Athel -- French and British, living in Marseilles for 37 years; mainly
in England until 1987.

Peter Moylan wrote:

> On 04/04/24 17:37, bertietaylor wrote:
>> Peter Moylan wrote:

>>> His starting point is that the equations of General Relativity
>>> work equally well with time running forwards or backwards. So far,
>>> that's in agreement with mainstream thinking. But from this he
>>> creates a scenario where matter that falls into a black hole can
>>> get close to the singularity, in a region where General Relativity
>>> does not hold, and then be time-reversed and bounce back out as the
>>> product of a white hole.
>>
>>> [My immediate reaction: if a time-reversed object travels out of
>>> the hole, then those of us who live forward in time will see it as
>>> falling into the hole. But maybe I've missed his point.]
>>
>>> What is the reason such a bounce is possible? Well, Dante
>>> explained that. You can travel down to the innermost part of Hell,
>>> and there you will find ... not a singularity, but a way to exit
>>> from Hell. QED.
>>
>>> Have I missed seeing something important?
>>
>> Gravitons!
>>
>> They are the basic to quantum entanglement. In a quantum entangled
>> world, one can assume that gravitons fill the void called space, with
>> instantaneous communication from any point to the other. The ancient
>> "action at a distance" principle for gravity remains valid!!!!!

> Traditional action at a distance has a time delay. For example, if an
> electron suddenly came into existence, the resulting change in the
> electric field would propagate outwards at the speed of light. The
> concept of quantum entanglement is upsetting because it suggests that
> information can be communicated at greater than the speed of light.

That's one way to approach it, but not popular among physicists at all,
I believe.

> That, in turn, says that Special Relativity is wrong. Which brings a
> whole lot of theory tumbling down ... is Arindam reading this?

There are no problems with SR, as I understand it. If any information
is being communicated faster than c, you can't use it to send
messages.

> Long-distance communication via gravity waves does assume a time delay,
> so it's not a quantum entanglement effect. As I understand it, quantum
> entanglement does not allow any information transfer, and that's how a
> paradox is avoided.

>> It is charming to bring in an ancient poet to a modern physics
>> discussion. What wonderful insights great poets have!

> Charming? From an artistic viewpoint, yes. But I reject the suggestion
> that Dante's opinions had any relationship to reality.

Well, I have sometimes suggested to my students that the gravitational
attraction between two bodies is l'amor che move il sol e' l'altre stelle.

--
Jerry Friedman

On 2024-04-04 13:35:11 +0000, jerryfriedman said:

> Peter Moylan wrote:
>
>> On 04/04/24 17:37, bertietaylor wrote:
>>> Peter Moylan wrote:
>
>>>> His starting point is that the equations of General Relativity
>>>> work equally well with time running forwards or backwards. So far,
>>>> that's in agreement with mainstream thinking. But from this he
>>>> creates a scenario where matter that falls into a black hole can
>>>> get close to the singularity, in a region where General Relativity
>>>> does not hold, and then be time-reversed and bounce back out as the
>>>> product of a white hole.
>>>
>>>> [My immediate reaction: if a time-reversed object travels out of
>>>> the hole, then those of us who live forward in time will see it as
>>>> falling into the hole. But maybe I've missed his point.]
>>>
>>>> What is the reason such a bounce is possible? Well, Dante
>>>> explained that. You can travel down to the innermost part of Hell,
>>>> and there you will find ... not a singularity, but a way to exit
>>>> from Hell. QED.
>>>
>>>> Have I missed seeing something important?
>>>
>>> Gravitons!
>>>
>>> They are the basic to quantum entanglement. In a quantum entangled
>>> world, one can assume that gravitons fill the void called space, with
>>> instantaneous communication from any point to the other. The ancient
>>> "action at a distance" principle for gravity remains valid!!!!!
>
>> Traditional action at a distance has a time delay. For example, if an
>> electron suddenly came into existence, the resulting change in the
>> electric field would propagate outwards at the speed of light. The
>> concept of quantum entanglement is upsetting because it suggests that
>> information can be communicated at greater than the speed of light.
>
> That's one way to approach it, but not popular among physicists at all,
> I believe.
>
>> That, in turn, says that Special Relativity is wrong. Which brings a
>> whole lot of theory tumbling down ... is Arindam reading this?
>
> There are no problems with SR, as I understand it. If any information
> is being communicated faster than c, you can't use it to send
> messages.

Suppose I had a laser source powerful enough to leave a reflection on
the moon, and suppose I change the angle slightly -- not enough to move
the reflection off the moon, but enough to move it faster than c. Could
I use it to transmit information? No, because there is no information
involved.
>
>> Long-distance communication via gravity waves does assume a time delay,
>> so it's not a quantum entanglement effect. As I understand it, quantum
>> entanglement does not allow any information transfer, and that's how a
>> paradox is avoided.
>
>>> It is charming to bring in an ancient poet to a modern physics
>>> discussion. What wonderful insights great poets have!
>
>> Charming? From an artistic viewpoint, yes. But I reject the suggestion
>> that Dante's opinions had any relationship to reality.
>
> Well, I have sometimes suggested to my students that the gravitational
> attraction between two bodies is l'amor che move il sol e' l'altre stelle.

--
Athel -- French and British, living in Marseilles for 37 years; mainly
in England until 1987.

On 04/04/2024 15:16, Athel Cornish-Bowden wrote:

> I think Arindam gave up on this group long ago because he couldn't find
> anyone to accept his claptrap.

I think he was forced to give up this group (an others) because he was
posting via GG. Like one other ex-poster, he could not figure out how to
post using a proper user agent.

> He's recently become quite noticeable at
> sci.physics.relativity.

Are you sure? How recently? Look at his latest post and let us know
what he is using as a user agent - if not GG?

On 04/04/2024 08:37, bertietaylor wrote:
> Peter Moylan wrote:
>
>> I've just finished reading the book "White Holes" by Carlo Rovelli, and
>> it's left me seriously puzzled. Is anyone else familiar with this book?
>
>>  From all the evidence available to me, Rovelli appears to be recognised
>> as a respectable physicist, not at all the sort of person who makes
>> u-tube videos about rail guns. The book, on the other hand, is written
>> in a style that one would expect from a deluded crackpot. His arguments
>> are partly from analogy, and partly from the numerous references to
>> Dante's /Divine Comedy/. I'll concede that one shouldn't expect
>> scientific rigour in a popular science book, but Rovelli falls over
>> backwards to avoid any concession to logical reasoning.
>
>> For those that haven't heard of them, white holes are the opposite of
>> black holes. Matter than passes the event horizon of a black hole can't
>> return, because of the extreme gravity. But matter can't enter a white
>> hole, it can only exit. From this one would expect a white hole to
>> radiate lots of energy. But no, Rovelli seems to say that from the
>> outside a white hole would look just like a black hole. (He gives no
>> justification for this assertion.) White holes have not yet been
>> observed, but given the time distortions around a black hole singularity
>> one might expect them to appear only after an infinite amount of time
>> has passed. That last sentence is my comment, not Rovelli's.
>
>> His starting point is that the equations of General Relativity work
>> equally well with time running forwards or backwards. So far, that's in
>> agreement with mainstream thinking. But from this he creates a scenario
>> where matter that falls into a black hole can get close to the
>> singularity, in a region where General Relativity does not hold, and
>> then be time-reversed and bounce back out as the product of a white hole.
>
>> [My immediate reaction: if a time-reversed object travels out of the
>> hole, then those of us who live forward in time will see it as falling
>> into the hole. But maybe I've missed his point.]
>
>> What is the reason such a bounce is possible? Well, Dante explained
>> that. You can travel down to the innermost part of Hell, and there you
>> will find ... not a singularity, but a way to exit from Hell. QED.
>
>> Have I missed seeing something important?
>
> Gravitons!

Gravitons are what account for gravitational forces in our current
model. If a 'white hole' existed which was spewing out matter, then it
would do so with anti-gravitons. How else would matter be ejected if not
by some anti-gravity force?

>
> They are the basic to quantum entanglement.
> In a quantum entangled world, one can assume that gravitons fill the void
> called space, with instantaneous communication from any point to the other.
> The ancient "action at a distance" principle for gravity remains valid!!!!!
>

<snip>

On 2024-04-04 14:54:17 +0000, occam said:

> On 04/04/2024 15:16, Athel Cornish-Bowden wrote:
>
>> I think Arindam gave up on this group long ago because he couldn't find
>> anyone to accept his claptrap.
>
> I think he was forced to give up this group (an others) because he was
> posting via GG. Like one other ex-poster, he could not figure out how to
> post using a proper user agent.
>
>> He's recently become quite noticeable at
>> sci.physics.relativity.
>
> Are you sure? How recently? Look at his latest post and let us know
> what he is using as a user agent - if not GG?

I can't find a post to check, but next time see one I'll let you know.
Maybe I'll release him (temporally) from my killfile.

--
Athel -- French and British, living in Marseilles for 37 years; mainly
in England until 1987.

On 2024-04-04 15:36:54 +0000, Athel Cornish-Bowden said:

> On 2024-04-04 14:54:17 +0000, occam said:
>
>> On 04/04/2024 15:16, Athel Cornish-Bowden wrote:
>>
>>> I think Arindam gave up on this group long ago because he couldn't find
>>> anyone to accept his claptrap.
>>
>> I think he was forced to give up this group (an others) because he was
>> posting via GG. Like one other ex-poster, he could not figure out how to
>> post using a proper user agent.
>>
>>> He's recently become quite noticeable at
>>> sci.physics.relativity.
>>
>> Are you sure? How recently? Look at his latest post and let us know
>> what he is using as a user agent - if not GG?
>
> I can't find a post to check, but next time see one I'll let you know.
> Maybe I'll release him (temporally) from my killfile.

Oh de ar. I thought there was something wrong with "temporally" when I
wrote it, but I couldn't work out what it was: temporarily, of course.

--
Athel -- French and British, living in Marseilles for 37 years; mainly
in England until 1987.

On 04-Apr-24 14:16, Athel Cornish-Bowden wrote:
>
> I think Arindam gave up on this group long ago because he couldn't find
> anyone to accept his claptrap. He's recently become quite noticeable at
> sci.physics.relativity. He doesn't convince the real scentists there
> either, but there are lots of crackpots who may take him seriously.

I wonder about that last suggestion.
Do crackpots of different stripes take each other seriously?

I suspect that if someone fails to share their exact idée fixe, then
they just fall into the "misguided fools" bracket = along with the rest
of humanity.

--
Sam Plusnet

Peter Moylan <peter@pmoylan.org.invalid> wrote:

> I've just finished reading the book "White Holes" by Carlo Rovelli, and
> it's left me seriously puzzled. Is anyone else familiar with this book?
>
> From all the evidence available to me, Rovelli appears to be recognised
> as a respectable physicist, not at all the sort of person who makes
> u-tube videos about rail guns. The book, on the other hand, is written
> in a style that one would expect from a deluded crackpot. His arguments
> are partly from analogy, and partly from the numerous references to
> Dante's /Divine Comedy/. I'll concede that one shouldn't expect
> scientific rigour in a popular science book, but Rovelli falls over
> backwards to avoid any concession to logical reasoning.

Rovelli certainly is to be taken seriously as a scientist.
(if you think people doing loop quantum gravity
are to be taken seriously)
He is also good at putting up popular performances,
and he can also be quite reasonable, if he wants to.

> For those that haven't heard of them, white holes are the opposite of
> black holes. Matter than passes the event horizon of a black hole can't
> return, because of the extreme gravity. But matter can't enter a white
> hole, it can only exit. From this one would expect a white hole to
> radiate lots of energy. But no, Rovelli seems to say that from the
> outside a white hole would look just like a black hole. (He gives no
> justification for this assertion.) White holes have not yet been
> observed, but given the time distortions around a black hole singularity
> one might expect them to appear only after an infinite amount of time
> has passed. That last sentence is my comment, not Rovelli's.

White holes are basically unphysical,
in the sense that they destroy all causality.
There interior is inaccessible in principle,
so we cannot know what will come out and why.
Elvis could come out driving a pink Cadillac, for all we know,

Jan

occam <occam@nowhere.nix> wrote:

> On 04/04/2024 15:16, Athel Cornish-Bowden wrote:
>
> > I think Arindam gave up on this group long ago because he couldn't find
> > anyone to accept his claptrap.
>
> I think he was forced to give up this group (an others) because he was
> posting via GG. Like one other ex-poster, he could not figure out how to
> post using a proper user agent.
>
> > He's recently become quite noticeable at
> > sci.physics.relativity.
>
> Are you sure? How recently? Look at his latest post and let us know
> what he is using as a user agent - if not GG?

He is using NemoWeb, like many other Google escapees,
Used to post to sci.physics, but that group has been taken over
completely by Russian trolls, so he has moved to sci.physics.relativity.
The content remains unchanged,

Jan

Sam Plusnet <not@home.com> wrote:

> On 04-Apr-24 14:16, Athel Cornish-Bowden wrote:
> >
> > I think Arindam gave up on this group long ago because he couldn't find
> > anyone to accept his claptrap. He's recently become quite noticeable at
> > sci.physics.relativity. He doesn't convince the real scentists there
> > either, but there are lots of crackpots who may take him seriously.
>
> I wonder about that last suggestion.
> Do crackpots of different stripes take each other seriously?

Usually not. They will agree in their contemt for 'standard' science,
but they will disagree on what is to replace it.

For the rest they usually are too busy pushing their own thing
to have much time for fighting others,

Jan

On 05/04/24 04:00, Athel Cornish-Bowden wrote:
> On 2024-04-04 15:36:54 +0000, Athel Cornish-Bowden said:

>> I can't find a post to check, but next time see one I'll let you
>> know. Maybe I'll release him (temporally) from my killfile.
>
> Oh de ar. I thought there was something wrong with "temporally"
> when I wrote it, but I couldn't work out what it was: temporarily, of
> course.

I thought you might be drawing a distinction between a time-like release
and a space-like release.

--
Peter Moylan http://www.pmoylan.org
Newcastle, NSW

On 05/04/24 06:16, Sam Plusnet wrote:
> On 04-Apr-24 14:16, Athel Cornish-Bowden wrote:
>>
>> I think Arindam gave up on this group long ago because he couldn't
>> find anyone to accept his claptrap. He's recently become quite
>> noticeable at sci.physics.relativity. He doesn't convince the real
>> scentists there either, but there are lots of crackpots who may
>> take him seriously.
>
> I wonder about that last suggestion. Do crackpots of different
> stripes take each other seriously?
>
> I suspect that if someone fails to share their exact idée fixe, then
> they just fall into the "misguided fools" bracket = along with the
> rest of humanity.

I was going to agree with you, but then I thought of an example. Isn't
the Trump phenomenon an example of a crackpot successfully recruiting
other crackpots?

--
Peter Moylan http://www.pmoylan.org
Newcastle, NSW

On 05/04/24 00:35, jerryfriedman wrote:
> Peter Moylan wrote:
>> On 04/04/24 17:37, bertietaylor wrote:

>> Traditional action at a distance has a time delay. For example, if
>> an electron suddenly came into existence, the resulting change in
>> the electric field would propagate outwards at the speed of light.
>> The concept of quantum entanglement is upsetting because it
>> suggests that information can be communicated at greater than the
>> speed of light.
>
> That's one way to approach it, but not popular among physicists at
> all, I believe.
>
>> That, in turn, says that Special Relativity is wrong. Which brings
>> a whole lot of theory tumbling down ... is Arindam reading this?
>
> There are no problems with SR, as I understand it. If any
> information is being communicated faster than c, you can't use it to
> send messages.

Yes, of course. I had temporarily forgotten that detail.

That is just like a detail that used to bother some of my students when
I was teaching them about waveguides. A sinusoidal wave in a waveguide
has both a phase velocity v_ph and a group velocity v_g, related by
v_ph x v_g = c^2
The group velocity is always less than c, and the phase velocity is
always greater than c. A velocity greater than c? How can that be? One
way to resolve the paradox is to put some modulation on the sine wave.
It turns out that the modulation always travels at the group velocity.

Without modulation, a pure sine wave carries no information, so there is
no paradox to explain.

>>> It is charming to bring in an ancient poet to a modern physics
>>> discussion. What wonderful insights great poets have!
>
>> Charming? From an artistic viewpoint, yes. But I reject the
>> suggestion that Dante's opinions had any relationship to reality.
>
> Well, I have sometimes suggested to my students that the
> gravitational attraction between two bodies is l'amor che move il sol
> e' l'altre stelle.

An interesting viewpoint, and possibly even more believable than the
Higgs field. In any case, I must congratulate you for making the
students sit up and listen.

--
Peter Moylan http://www.pmoylan.org
Newcastle, NSW

On 05/04/24 02:04, occam wrote:
> On 04/04/2024 08:37, bertietaylor wrote:
>> Peter Moylan wrote:

>>> White holes have not yet been observed, but given the time
>>> distortions around a black hole singularity one might expect them
>>> to appear only after an infinite amount of time has passed. That
>>> last sentence is my comment, not Rovelli's.
>>
>>> His starting point is that the equations of General Relativity
>>> work equally well with time running forwards or backwards. So
>>> far, that's in agreement with mainstream thinking. But from this
>>> he creates a scenario where matter that falls into a black hole
>>> can get close to the singularity, in a region where General
>>> Relativity does not hold, and then be time-reversed and bounce
>>> back out as the product of a white hole.
>>
>>> [My immediate reaction: if a time-reversed object travels out of
>>> the hole, then those of us who live forward in time will see it
>>> as falling into the hole. But maybe I've missed his point.]
>>
>>> What is the reason such a bounce is possible? Well, Dante
>>> explained that. You can travel down to the innermost part of
>>> Hell, and there you will find ... not a singularity, but a way to
>>> exit from Hell. QED.
>>
>>> Have I missed seeing something important?
>>
>> Gravitons!
>
> Gravitons are what account for gravitational forces in our current
> model. If a 'white hole' existed which was spewing out matter, then
> it would do so with anti-gravitons. How else would matter be ejected
> if not by some anti-gravity force?

One thing that occurred to me while reading the book was that for white
holes to exist gravity must come in two flavours, one attractive and one
repulsive. After all, if electric charge can be either positive or
negative ... . Perhaps negative gravity was responsible for the
inflationary phase of the early universe.

Still, a crucial step in Rovelli's reasoning is the invocation of time
reversal. And, in reverse time, ordinary gravity is indeed repulsive.

--
Peter Moylan http://www.pmoylan.org
Newcastle, NSW

On 04-Apr-24 23:41, Peter Moylan wrote:
> On 05/04/24 06:16, Sam Plusnet wrote:
>> On 04-Apr-24 14:16, Athel Cornish-Bowden wrote:
>>>
>>> I think Arindam gave up on this group long ago because he couldn't
>>>  find anyone to accept his claptrap. He's recently become quite
>>> noticeable at sci.physics.relativity. He doesn't convince the real
>>>  scentists there either, but there are lots of crackpots who may
>>> take him seriously.
>>
>> I wonder about that last suggestion. Do crackpots of different
>> stripes take each other seriously?
>>
>> I suspect that if someone fails to share their exact idée fixe, then
>>  they just fall into the "misguided fools" bracket = along with the
>> rest of humanity.
>
> I was going to agree with you, but then I thought of an example. Isn't
> the Trump phenomenon an example of a crackpot successfully recruiting
> other crackpots?

It's hard to argue with a Trump example.

Not a direct response to your post, but I am starting to wonder if we
need some Trumpian variant on Godwin's Law?

--
Sam Plusnet

On 05/04/24 08:04, J. J. Lodder wrote:

> White holes are basically unphysical, in the sense that they destroy
> all causality. There interior is inaccessible in principle, so we
> cannot know what will come out and why. Elvis could come out driving
> a pink Cadillac, for all we know,

This whole discussion reminds me of a question that I've never found the
answer to. Hawking radiation causes a black hole gradually to lose
mass/energy. After a very long time, is it possible for a black hole to
lose so much mass that it can no longer support an event horizon and a
singularity, putting it back into the "normal" universe? Somebody here
probably knows the answer.

I guess the answer depends on the interplay of mass, event horizon
radius (as seen by an outside observer), and energy loss.

--
Peter Moylan http://www.pmoylan.org
Newcastle, NSW

Peter Moylan wrote:

> On 05/04/24 08:04, J. J. Lodder wrote:

>> White holes are basically unphysical, in the sense that they destroy
>> all causality. There interior is inaccessible in principle, so we
>> cannot know what will come out and why. Elvis could come out driving
>> a pink Cadillac, for all we know,

> This whole discussion reminds me of a question that I've never found the
> answer to. Hawking radiation causes a black hole gradually to lose
> mass/energy. After a very long time, is it possible for a black hole to
> lose so much mass that it can no longer support an event horizon and a
> singularity, putting it back into the "normal" universe? Somebody here
> probably knows the answer.

> I guess the answer depends on the interplay of mass, event horizon
> radius (as seen by an outside observer), and energy loss.

Hawking radiation is not firmly established on theoretical grounds.
If it exists, the temperature of the black hole increases with decreasing
radius, so the rate of energy loss is initially very slow but gets faster
until the whole tiny thing disappears with a bang. People have looked
for those gamma-ray bangs, conceivably produced by microscopic
black holes conceivably produced in the early universe, but haven't
found any.

--
Jerry Friedman