Re: The size of the universe

[Jason Resch]

On Tue, May 26, 2020 at 11:16 PM 'Brent Meeker' via Everything List <
everything-list@googlegroups.com> wrote:

>
>
> On 5/26/2020 3:33 PM, Jason Resch wrote:
>
>
>
> On Wed, May 20, 2020 at 5:14 PM 'Brent Meeker' via Everything List <
> everything-list@googlegroups.com> wrote:
>
>>
>>
>> On 5/20/2020 6:39 AM, Bruno Marchal wrote:
>> > Hi Jason,
>> >
>> > When you say that Reality is infinite, are you alluding to the
>> > (phenomenological) physical reality? Or the absolute reality?
>> >
>> > With mechanism, it is very plausible that the physical reality is
>> > infinite, as it is a sort of broder of the universal mind (the mind of
>> > the “virgin” universal machine).
>> >
>> > But even with an infinite physical reality, it is unclear if we are
>> > alone or not, in the physical reality. We are numerous in the
>> > arithmetical reality (which can be taken as the absolute one, modulo a
>> > change of universal machinery). But to have alien fellows in the
>> > physical reality, you need some homogeneity in that reality, which is
>> > not obvious at first sight.
>> >
>> > In fact, I get the impression that we might be rare, if not alone. The
>> > probability for life might be as close to zero as von Neumann thought,
>> > but even the possibility of its evolution requires many conditions, so
>> > many that we might be alone in the cosmos (not in the multiverse, as
>> > there we have even doppelangers).
>>
>> I think the evidence suggests that there is a lot of life in the visible
>> universe and even a lot of technological civilizations...but they are so
>> sparse that we are effectively alone.
>>
>>
> Hi Brent,
>
> As promised I've just finished writing about the existence of life and
> intelligent life in the universe. I'd appreciate your thoughts.
>
> Though life could be very rare I describe another possibility, which is
> that it miniaturizes and becomes so unlike and alient to the biological
> life we're familiar with and looking for that we don't notice it.
>
>
> But we do know that even the most microscopic "life", even viruses grow
> and reproduce using the same mechanism at the molecular level as we do:
> DNA, RNA, mRNA, proteins, ATP=>ADp,...  That's really the basis for
> thinking that all life on Earth had a single origin.  Even archea and
> bacteria use the same metabolic pathways.
>
>
I agree life will likely start in more or less recognizable ways, but I
believe that after a few thousand or million years of being a technological
civilization, it will reach stages that are unrecognizable to us. They will
most likely be non-biological, and non-corporeal, living in virtual
realities. Computers are substrate independent and can take many different
forms. Moreover they can be arbitrarily efficient so long as they are
logically reversible. There need not be any significant heat signature.


>
> https://alwaysasking.com/are-we-alone/
>
>
> Not just matter, energy, and time.  Life needs an entropy gradient.  Your
> whole section on "Energy" reads as though energy is consumed.  But energy
> is conserved.
>

Good point. I meant energy in the colloquial sense (energy available for
useful work). Is there a another word I could use for this concept that
isn't as technical/scary sounding as entropy gradient?


> It is low entropy (mostly of sunlight) that is "consumed" by turning it
> into higher entropy infrared radiation.  The best theories of the origin of
> life postulate alkaline vents as the locus (which are not so hot as
> hydrothermal vents).  Have you read Nick Lane's "The Vital Question"?
>

I haven't. Thanks for the suggestions, I will have to read more about
alkaline vents.


>
> I think you make a mistake in jumping right into "what life needs".  You
> should first define what you mean by life.  Life as we know it: carbon,
> hydrogen based?  Anything that reproduces.  Anything that
> metabolizes?...what?
>

You're right, that is an oversight. I will add a definition. Something
like: self-maintaining processes that convey information across generations.


>
> It took a billion to two billion years for* eukaryotes* to evolve...not
> multicellular life.  Multicellular life only arose 0.6 billion ya.
>

Thank you, I will correct this.


>
> Tardigrades are not going to survive on the Moon...that's fantasy.  They
> don't eat rocks. Surface temperature on the Moon near the equator varies
> from -183 degC to +106degC.  And there's no protection from occassional
> cosmic ray showers.  Tardigrades might survive hours or weeks, but they are
> not going to survive as a species on the Moon.
>

The Tardigrades were in their tun state where they wrap up their genes to
protect them from radiation and reduce their metabolism by orders of
magnitude. I agree they would not thrive and reproduce on the moon, but
they may exist for perhaps a year (maybe longer?), at least if some landed
in an indentation in the soil where they were shielded from direct
sunlight) and remain revivable. Some recovered tardigrades in t

Re: The size of the universe

['Brent Meeker' via Everything List]

On 5/26/2020 3:33 PM, Jason Resch wrote:



On Wed, May 20, 2020 at 5:14 PM 'Brent Meeker' via Everything List 
> wrote:




On 5/20/2020 6:39 AM, Bruno Marchal wrote:
> Hi Jason,
>
> When you say that Reality is infinite, are you alluding to the
> (phenomenological) physical reality? Or the absolute reality?
>
> With mechanism, it is very plausible that the physical reality is
> infinite, as it is a sort of broder of the universal mind (the
mind of
> the “virgin” universal machine).
>
> But even with an infinite physical reality, it is unclear if we are
> alone or not, in the physical reality. We are numerous in the
> arithmetical reality (which can be taken as the absolute one,
modulo a
> change of universal machinery). But to have alien fellows in the
> physical reality, you need some homogeneity in that reality,
which is
> not obvious at first sight.
>
> In fact, I get the impression that we might be rare, if not
alone. The
> probability for life might be as close to zero as von Neumann
thought,
> but even the possibility of its evolution requires many
conditions, so
> many that we might be alone in the cosmos (not in the
multiverse, as
> there we have even doppelangers).

I think the evidence suggests that there is a lot of life in the
visible
universe and even a lot of technological civilizations...but they
are so
sparse that we are effectively alone.


Hi Brent,

As promised I've just finished writing about the existence of life and 
intelligent life in the universe. I'd appreciate your thoughts.


Though life could be very rare I describe another possibility, which 
is that it miniaturizes and becomes so unlike and alient to the 
biological life we're familiar with and looking for that we don't 
notice it.


But we do know that even the most microscopic "life", even viruses grow 
and reproduce using the same mechanism at the molecular level as we do: 
DNA, RNA, mRNA, proteins, ATP=>ADp,...  That's really the basis for 
thinking that all life on Earth had a single origin. Even archea and 
bacteria use the same metabolic pathways.




https://alwaysasking.com/are-we-alone/


Not just matter, energy, and time.  Life needs an entropy gradient. Your 
whole section on "Energy" reads as though energy is consumed. But energy 
is conserved.  It is low entropy (mostly of sunlight) that is "consumed" 
by turning it into higher entropy infrared radiation.  The best theories 
of the origin of life postulate alkaline vents as the locus (which are 
not so hot as hydrothermal vents).  Have you read Nick Lane's "The Vital 
Question"?


I think you make a mistake in jumping right into "what life needs". You 
should first define what you mean by life.  Life as we know it: carbon, 
hydrogen based?  Anything that reproduces.  Anything that 
metabolizes?...what?


It took a billion to two billion years for/*eukaryotes*/ to evolve...not 
multicellular life.  Multicellular life only arose 0.6 billion ya.


Tardigrades are not going to survive on the Moon...that's fantasy. They 
don't eat rocks. Surface temperature on the Moon near the equator varies 
from -183 degC to +106degC.  And there's no protection from occassional 
cosmic ray showers.  Tardigrades might survive hours or weeks, but they 
are not going to survive as a species on the Moon.


The Drake equation rewritten in terms of "detectable" civilizations is 
wrong because it only considers sending out signals.  To be detectable 
there has to be a receiver in the forward light cone. Assuming 
technologically advanced civilizations last 500yrs that means two of 
them have to be withing detection range during that 500yr band.  I'm not 
sure what the detection range is within a noisy galaxy but I think it's 
less than 100lyr.  One problem is that as communication becomes more 
technologically advance it becomes less distinguishable from noise.


 "the Arecibo Telescope on the receiving end could pick up the signal 
from a distance of tens of thousand of light years–on the other side of 
the galaxy."

The other side of the galaxy is a /*hundred*/ thousand light years away.

"The vast distances implied by being the only intelligence in the 
observable universe would, for all practical purposes, mean we are 
alone, even if infinite other intelligences exist across our infinite 
universe."
I think this is the important take-home point.  And it doesn't have much 
to do with the observable universe and how many planets may have life.  
Even the closest stars are already too far away for us to not be alone.  
We might conceivably send a probe to alpha centauri.  We might talk to a 
technological civilization 50 light years away...but that would be about 
the limit, 100year send/reply cycle.


No doubt intelligence is evolutionarily useful...but human level 
intelligence, speech, mathematics, techno

Re: Coordinate time vs Proper time

['Brent Meeker' via Everything List]

On 5/26/2020 6:49 AM, Alan Grayson wrote:



On Tuesday, May 26, 2020 at 5:51:50 AM UTC-6, Alan Grayson wrote:



On Sunday, May 24, 2020 at 4:49:48 PM UTC-6, Brent wrote:



On 5/24/2020 11:21 AM, Alan Grayson wrote:



On Sunday, May 24, 2020 at 8:51:35 AM UTC-6, Alan Grayson wrote:



On Saturday, May 23, 2020 at 12:06:33 PM UTC-6, Brent wrote:



On 5/22/2020 11:25 PM, Alan Grayson wrote:



On Friday, May 22, 2020 at 11:03:40 PM UTC-6, Brent
wrote:



On 5/22/2020 9:48 PM, Alan Grayson wrote:



On Friday, May 22, 2020 at 9:05:23 PM UTC-6,
Brent wrote:



On 5/22/2020 6:26 PM, Alan Grayson wrote:



On Monday, May 18, 2020 at 3:28:40 PM
UTC-6, Alan Grayson wrote:

Suppose the universe is a
hyper-sphere, not expanding, and an
observer travels on a closed loop and
returns to his spatial starting point.
His elapsed or proper time will be
finite, but what is his coordinate
time at the end of the journey?  TIA, AG


It's not a dumb question IMO. If you
circumnavigate a spherical non-expanding
universe, what happens to coordinate time
at the end of the journey? Does something
update the time coordinate? Or does it
somehow miraculously(?) remain fixed? TIA, AG


Are you supposing the universe is a
3-sphere?  In that case It's just like
going around a circle.  The degree marks on
the circle are coordinates, they have no
physical meaning except to label points. 
So if you walk around the circle you
measure a certain distance (proper time)
but come back to the same point.

Or are you supposing it's a 4-sphere so
that all geodesics are closed time-like
curves?  I don't know how that would work. 
I don't think there's any solution of that
form to Einstein's equations.

Brent


I'm supposing a 4-sphere and (I think) closed
time-like curves. The traveler returns
presumably to his starting position, but is the
time coordinate unchanged? AG


I don't think there's any very sensible answer
in that case. Goedel showed there can be
solutions with closed time-like curves if the
universe is rotating.  But solutions of GR don't
have any dynamic connection to matter and the
entropy of matter.  In the same spirit there
could be a solution to quantum field theory that
was close around the time like curve...in which
case you'd experience "Groundhog
Day"...including your thoughts.

Brent


What does entropy have to do with this problem? AG


Increasing entropy points the direction of time.

Brent


Let me pose the question another way: Is coordinate time
ever updated? AG


Or say, in the Twin Paradox, the elapsed or proper time for
the traveling twin is less than for the Earth-bound twin, but
when they meet, do they share the same coordinate time? AG


Yes.  Coordinates are labels for points, so if you're together
with your twin, you both are at the same point in spacetime
and that point only has one label in any given coordinate system.

Brent


Since time is just ONE of the 4 labels for spacetime points, can
they be assigned at random? What specific function do they
satisfy? AG


How is the time coordinate chosen such that the Lorentz distance 
between spacetime points is meaningful? AG


The proper distance/duration is an invariant, it doesn't depend on the 
coordinate system.


Brent

--
You received this message because you are subscribed to the Google Groups 
"Everything List" group.
To unsubscribe from this group and stop receiving emails from it, send an email 
to everything-list+unsubscr...@googlegroups.com.
To view this discussion on the web visit 
https://groups.google.com/d/msgid/everything-list/7533e9aa-8c9a-842b-6f25-29ab4695e05d%40verizon.net.

Re: The size of the universe

[Jason Resch]

On Wed, May 20, 2020 at 5:14 PM 'Brent Meeker' via Everything List <
everything-list@googlegroups.com> wrote:

>
>
> On 5/20/2020 6:39 AM, Bruno Marchal wrote:
> > Hi Jason,
> >
> > When you say that Reality is infinite, are you alluding to the
> > (phenomenological) physical reality? Or the absolute reality?
> >
> > With mechanism, it is very plausible that the physical reality is
> > infinite, as it is a sort of broder of the universal mind (the mind of
> > the “virgin” universal machine).
> >
> > But even with an infinite physical reality, it is unclear if we are
> > alone or not, in the physical reality. We are numerous in the
> > arithmetical reality (which can be taken as the absolute one, modulo a
> > change of universal machinery). But to have alien fellows in the
> > physical reality, you need some homogeneity in that reality, which is
> > not obvious at first sight.
> >
> > In fact, I get the impression that we might be rare, if not alone. The
> > probability for life might be as close to zero as von Neumann thought,
> > but even the possibility of its evolution requires many conditions, so
> > many that we might be alone in the cosmos (not in the multiverse, as
> > there we have even doppelangers).
>
> I think the evidence suggests that there is a lot of life in the visible
> universe and even a lot of technological civilizations...but they are so
> sparse that we are effectively alone.
>
>
Hi Brent,

As promised I've just finished writing about the existence of life and
intelligent life in the universe. I'd appreciate your thoughts.

Though life could be very rare I describe another possibility, which is
that it miniaturizes and becomes so unlike and alient to the biological
life we're familiar with and looking for that we don't notice it.

https://alwaysasking.com/are-we-alone/

Jason

-- 
You received this message because you are subscribed to the Google Groups 
"Everything List" group.
To unsubscribe from this group and stop receiving emails from it, send an email 
to everything-list+unsubscr...@googlegroups.com.
To view this discussion on the web visit 
https://groups.google.com/d/msgid/everything-list/CA%2BBCJUjDVPtfaCAoObhmT%2BtxwzC97mnzaU%2BqRVkMd_UeNF5Neg%40mail.gmail.com.

Re: Coordinate time vs Proper time

['Brent Meeker' via Everything List]

On 5/26/2020 4:51 AM, Alan Grayson wrote:



On Sunday, May 24, 2020 at 4:49:48 PM UTC-6, Brent wrote:



On 5/24/2020 11:21 AM, Alan Grayson wrote:



On Sunday, May 24, 2020 at 8:51:35 AM UTC-6, Alan Grayson wrote:



On Saturday, May 23, 2020 at 12:06:33 PM UTC-6, Brent wrote:



On 5/22/2020 11:25 PM, Alan Grayson wrote:



On Friday, May 22, 2020 at 11:03:40 PM UTC-6, Brent wrote:



On 5/22/2020 9:48 PM, Alan Grayson wrote:



On Friday, May 22, 2020 at 9:05:23 PM UTC-6, Brent
wrote:



On 5/22/2020 6:26 PM, Alan Grayson wrote:



On Monday, May 18, 2020 at 3:28:40 PM UTC-6,
Alan Grayson wrote:

Suppose the universe is a hyper-sphere,
not expanding, and an observer travels on
a closed loop and returns to his spatial
starting point. His elapsed or proper time
will be finite, but what is his coordinate
time at the end of the journey? TIA, AG


It's not a dumb question IMO. If you
circumnavigate a spherical non-expanding
universe, what happens to coordinate time at
the end of the journey? Does something update
the time coordinate? Or does it somehow
miraculously(?) remain fixed? TIA, AG


Are you supposing the universe is a 3-sphere? 
In that case It's just like going around a
circle.  The degree marks on the circle are
coordinates, they have no physical meaning
except to label points.  So if you walk around
the circle you measure a certain distance
(proper time) but come back to the same point.

Or are you supposing it's a 4-sphere so that
all geodesics are closed time-like curves?  I
don't know how that would work. I don't think
there's any solution of that form to Einstein's
equations.

Brent


I'm supposing a 4-sphere and (I think) closed
time-like curves. The traveler returns presumably
to his starting position, but is the time
coordinate unchanged? AG


I don't think there's any very sensible answer in
that case.  Goedel showed there can be solutions
with closed time-like curves if the universe is
rotating.  But solutions of GR don't have any
dynamic connection to matter and the entropy of
matter.  In the same spirit there could be a
solution to quantum field theory that was close
around the time like curve...in which case you'd
experience "Groundhog Day"...including your thoughts.

Brent


What does entropy have to do with this problem? AG


Increasing entropy points the direction of time.

Brent


Let me pose the question another way: Is coordinate time ever
updated? AG


Or say, in the Twin Paradox, the elapsed or proper time for the
traveling twin is less than for the Earth-bound twin, but when
they meet, do they share the same coordinate time? AG


Yes.  Coordinates are labels for points, so if you're together
with your twin, you both are at the same point in spacetime and
that point only has one label in any given coordinate system.

Brent


Since time is just of the 4 labels for spacetime points, can they be 
assigned at random? What specific function do they satisfy? AG


They're not assigned at random because they need to form a locally 
smooth flat tangent space so that Einstein's equations will apply. And 
that's their function...they label in the points so that the equations 
apply and when you solve the equations you will know what value goes 
with what point.


Brent

--
You received this message because you are subscribed to the Google Groups 
"Everything List" group.
To unsubscribe from this group and stop receiving emails from it, send an email 
to everything-list+unsubscr...@googlegroups.com.
To view this discussion on the web visit 
https://groups.google.com/d/msgid/everything-list/d9a7d34b-a98c-f723-19db-50a59da0f686%40verizon.net.

Re: STEP 3

[smitra]

On 23-05-2020 23:01, 'Brent Meeker' via Everything List wrote:

On 5/23/2020 11:51 AM, smitra wrote:


My point is that identity is an intrinsic property of what
something
is now. The history of the of the constituent particles have no
affect
on the behaviors or operation of those particles. To say the
history
is relevant to identity is to add an arbitrary extrinsic property
which can be of no physical relevance.

This is a direct consequence of QM, you can't distinguish two
electrons, from each other.
But they still have locations and histories, c.f. Griffiths
consistent
histories interpretation of QM or Feynmann's path integral QM.
When
electrons make spots on the film in an EPR experiment the electron

that made this spot is not identical with the electron that made
that
spot in the sense of being the same electron.  And in any case I
don't
see how the sameness of particles implies the sameness of  complex

structures made of particles, i.e. persons.

Brent


Physics is local, all the relevant information to describe what I
feel right now is contained in my brain at this exact moment. While
this can all be explained in terms of information in the past, that
doesn't take away from the fact that it is also present right here
in my head. Also, not all the information was present in the past
state due to effective collapse of the wavefunction. In general, I
end up in a superposition of states which has the exact same
information content as the past state. I then find myself in one of
the possible components of such a superposition (in the
computational basis states of the classical algorithm that my brain
is running).

Saibal


In the MWI, there is never any increase in the total information.  All
evolution is unitary and reversible.  Local information appears
because event horizons make correlations (negative information)
inaccessible.

Brent


That's the case for the global wavefunction. But if you are in a 
superposition of making a binary choice one way or the other with equal 
amplitudes, then you will find yourself in one or the other part of the 
superposition. So one bit of information appears in the sector you are 
in which is essentially the information needed to specify in what sector 
you are.


Saibal




 --
You received this message because you are subscribed to the Google
Groups "Everything List" group.
To unsubscribe from this group and stop receiving emails from it, send
an email to everything-list+unsubscr...@googlegroups.com.
To view this discussion on the web visit
https://groups.google.com/d/msgid/everything-list/38c447fd-6117-225e-415f-deae1cb728a9%40verizon.net
[1].


Links:
--
[1]
https://groups.google.com/d/msgid/everything-list/38c447fd-6117-225e-415f-deae1cb728a9%40verizon.net?utm_medium=email&utm_source=footer


--
You received this message because you are subscribed to the Google Groups 
"Everything List" group.
To unsubscribe from this group and stop receiving emails from it, send an email 
to everything-list+unsubscr...@googlegroups.com.
To view this discussion on the web visit 
https://groups.google.com/d/msgid/everything-list/a0cb942f948f36fe7e6a0a6603ab7379%40zonnet.nl.

The absurdity of nature ... and science

[Philip Thrift]

https://americanaffairsjournal.org/2020/05/science-without-validation-in-a-world-without-meaning/

@philipthrift 

-- 
You received this message because you are subscribed to the Google Groups 
"Everything List" group.
To unsubscribe from this group and stop receiving emails from it, send an email 
to everything-list+unsubscr...@googlegroups.com.
To view this discussion on the web visit 
https://groups.google.com/d/msgid/everything-list/7130f54a-9b83-4907-ace9-0dfd5b09bb21%40googlegroups.com.

Re: Coordinate time vs Proper time

[Alan Grayson]

On Tuesday, May 26, 2020 at 5:51:50 AM UTC-6, Alan Grayson wrote:
>
>
>
> On Sunday, May 24, 2020 at 4:49:48 PM UTC-6, Brent wrote:
>>
>>
>>
>> On 5/24/2020 11:21 AM, Alan Grayson wrote:
>>
>>
>>
>> On Sunday, May 24, 2020 at 8:51:35 AM UTC-6, Alan Grayson wrote: 
>>>
>>>
>>>
>>> On Saturday, May 23, 2020 at 12:06:33 PM UTC-6, Brent wrote: 



 On 5/22/2020 11:25 PM, Alan Grayson wrote:



 On Friday, May 22, 2020 at 11:03:40 PM UTC-6, Brent wrote: 
>
>
>
> On 5/22/2020 9:48 PM, Alan Grayson wrote:
>
>
>
> On Friday, May 22, 2020 at 9:05:23 PM UTC-6, Brent wrote: 
>>
>>
>>
>> On 5/22/2020 6:26 PM, Alan Grayson wrote:
>>
>>
>>
>> On Monday, May 18, 2020 at 3:28:40 PM UTC-6, Alan Grayson wrote: 
>>>
>>> Suppose the universe is a hyper-sphere, not expanding, and an 
>>> observer travels on a closed loop and returns to his spatial starting 
>>> point. His elapsed or proper time will be finite, but what is his 
>>> coordinate time at the end of the journey?  TIA, AG
>>>
>>
>> It's not a dumb question IMO. If you circumnavigate a spherical 
>> non-expanding universe, what happens to coordinate time at the end of 
>> the 
>> journey? Does something update the time coordinate? Or does it somehow 
>> miraculously(?) remain fixed? TIA, AG
>>
>>
>> Are you supposing the universe is a 3-sphere?  In that case It's just 
>> like going around a circle.  The degree marks on the circle are 
>> coordinates, they have no physical meaning except to label points.  So 
>> if 
>> you walk around the circle you measure a certain distance (proper time) 
>> but 
>> come back to the same point.
>>
>> Or are you supposing it's a 4-sphere so that all geodesics are closed 
>> time-like curves?  I don't know how that would work.  I don't think 
>> there's 
>> any solution of that form to Einstein's equations.
>>
>> Brent
>>
>
> I'm supposing a 4-sphere and (I think) closed time-like curves. The 
> traveler returns presumably to his starting position, but is the time 
> coordinate unchanged? AG 
>
>
> I don't think there's any very sensible answer in that case.  Goedel 
> showed there can be solutions with closed time-like curves if the 
> universe 
> is rotating.  But solutions of GR don't have any dynamic connection to 
> matter and the entropy of matter.  In the same spirit there could be a 
> solution to quantum field theory that was close around the time like 
> curve...in which case you'd experience "Groundhog Day"...including your 
> thoughts.
>
> Brent
>

 What does entropy have to do with this problem? AG 


 Increasing entropy points the direction of time.

 Brent

>>>
>>> Let me pose the question another way: Is coordinate time ever updated? 
>>> AG 
>>>
>>
>> Or say, in the Twin Paradox, the elapsed or proper time for the traveling 
>> twin is less than for the Earth-bound twin, but when they meet, do they 
>> share the same coordinate time? AG 
>>
>>
>> Yes.  Coordinates are labels for points, so if you're together with your 
>> twin, you both are at the same point in spacetime and that point only has 
>> one label in any given coordinate system.
>>
>> Brent
>>
>
> Since time is just ONE of the 4 labels for spacetime points, can they be 
> assigned at random? What specific function do they satisfy? AG 
>

How is the time coordinate chosen such that the Lorentz distance between 
spacetime points is meaningful? AG 

-- 
You received this message because you are subscribed to the Google Groups 
"Everything List" group.
To unsubscribe from this group and stop receiving emails from it, send an email 
to everything-list+unsubscr...@googlegroups.com.
To view this discussion on the web visit 
https://groups.google.com/d/msgid/everything-list/9932d47e-58c0-47a6-9ce9-24f786f8c168%40googlegroups.com.

Re: Coordinate time vs Proper time

[Alan Grayson]

On Sunday, May 24, 2020 at 4:49:48 PM UTC-6, Brent wrote:
>
>
>
> On 5/24/2020 11:21 AM, Alan Grayson wrote:
>
>
>
> On Sunday, May 24, 2020 at 8:51:35 AM UTC-6, Alan Grayson wrote: 
>>
>>
>>
>> On Saturday, May 23, 2020 at 12:06:33 PM UTC-6, Brent wrote: 
>>>
>>>
>>>
>>> On 5/22/2020 11:25 PM, Alan Grayson wrote:
>>>
>>>
>>>
>>> On Friday, May 22, 2020 at 11:03:40 PM UTC-6, Brent wrote: 



 On 5/22/2020 9:48 PM, Alan Grayson wrote:



 On Friday, May 22, 2020 at 9:05:23 PM UTC-6, Brent wrote: 
>
>
>
> On 5/22/2020 6:26 PM, Alan Grayson wrote:
>
>
>
> On Monday, May 18, 2020 at 3:28:40 PM UTC-6, Alan Grayson wrote: 
>>
>> Suppose the universe is a hyper-sphere, not expanding, and an 
>> observer travels on a closed loop and returns to his spatial starting 
>> point. His elapsed or proper time will be finite, but what is his 
>> coordinate time at the end of the journey?  TIA, AG
>>
>
> It's not a dumb question IMO. If you circumnavigate a spherical 
> non-expanding universe, what happens to coordinate time at the end of the 
> journey? Does something update the time coordinate? Or does it somehow 
> miraculously(?) remain fixed? TIA, AG
>
>
> Are you supposing the universe is a 3-sphere?  In that case It's just 
> like going around a circle.  The degree marks on the circle are 
> coordinates, they have no physical meaning except to label points.  So if 
> you walk around the circle you measure a certain distance (proper time) 
> but 
> come back to the same point.
>
> Or are you supposing it's a 4-sphere so that all geodesics are closed 
> time-like curves?  I don't know how that would work.  I don't think 
> there's 
> any solution of that form to Einstein's equations.
>
> Brent
>

 I'm supposing a 4-sphere and (I think) closed time-like curves. The 
 traveler returns presumably to his starting position, but is the time 
 coordinate unchanged? AG 


 I don't think there's any very sensible answer in that case.  Goedel 
 showed there can be solutions with closed time-like curves if the universe 
 is rotating.  But solutions of GR don't have any dynamic connection to 
 matter and the entropy of matter.  In the same spirit there could be a 
 solution to quantum field theory that was close around the time like 
 curve...in which case you'd experience "Groundhog Day"...including your 
 thoughts.

 Brent

>>>
>>> What does entropy have to do with this problem? AG 
>>>
>>>
>>> Increasing entropy points the direction of time.
>>>
>>> Brent
>>>
>>
>> Let me pose the question another way: Is coordinate time ever updated? AG 
>>
>
> Or say, in the Twin Paradox, the elapsed or proper time for the traveling 
> twin is less than for the Earth-bound twin, but when they meet, do they 
> share the same coordinate time? AG 
>
>
> Yes.  Coordinates are labels for points, so if you're together with your 
> twin, you both are at the same point in spacetime and that point only has 
> one label in any given coordinate system.
>
> Brent
>

Since time is just of the 4 labels for spacetime points, can they be 
assigned at random? What specific function do they satisfy? AG 

-- 
You received this message because you are subscribed to the Google Groups 
"Everything List" group.
To unsubscribe from this group and stop receiving emails from it, send an email 
to everything-list+unsubscr...@googlegroups.com.
To view this discussion on the web visit 
https://groups.google.com/d/msgid/everything-list/c7ccdfaf-cf9f-425e-863e-8491dddeb69c%40googlegroups.com.