The Mass-Luminosity Relationship

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Gene

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Oct 12, 2008, 4:31:30 PM10/12/08
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The mass-luminosity relationship for main-sequence stars was known dung all
of the Golden Age, and hence it was lnown that all of those sfnal Rigellians
and Denebians were nonsensical, Was this simply being ignored as so much was
ignored, or had the news not reached most sci-fi authors?

Joseph Nebus

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Oct 12, 2008, 6:33:54 PM10/12/08
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Gene <ge...@chewbacca.org> writes:

Are you sure the news has reached them by now?


In providing notes to Gene Roddenberry in making the pilot and
series bible for _Star Trek_, Kellam DeForest research noted that Rigel
and Sirius and such were unlikely stars to have habitable planets, but
that giving stars familiar and attractive names may be more important
to audience acceptance of the show.

I wouldn't be surprised if the same thing weren't discovered,
maybe not consciously, by everyone who's put Earth-like planets around
Rigel: science fiction stories aren't textbooks and it's more important
to sound interesting than to be scientifically rigorous.

--
Joseph Nebus
------------------------------------------------------------------------------

J. Clarke

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Oct 12, 2008, 6:32:03 PM10/12/08
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Or perhaps they assumed that some future researcher would find
Eddington to be in error, or perhaps on other worlds sentient life
just evolved a _lot_ faster, or perhaps something else.

--
--
--John
to email, dial "usenet" and validate
(was jclarke at eye bee em dot net)


Gene

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Oct 12, 2008, 7:17:29 PM10/12/08
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"J. Clarke" <jclarke...@cox.net> rote in
news:gctvh...@news7.newsguy.com:

> Or perhaps they assumed that some future researcher would find
> Eddington to be in error, or perhaps on other worlds sentient life
> just evolved a _lot_ faster, or perhaps something else.

Sadly, there was an observational as well as a theoretical basis, as the mass
of near-by double stars can be determined.

J. Clarke

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Oct 12, 2008, 8:12:16 PM10/12/08
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OK, you've lost me. I was assuming that you were basing your
objection to the use of Rigel and Deneb on their relatively short
lives, which was calculated assuming that they were powered by
hydrogen fusion and that the reaction released a certain quantity of
energy per unit mass.

If that is not your objection, then what is? I don't see how the mass
of the star, per se, is an issue.

Wayne Throop

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Oct 12, 2008, 9:11:09 PM10/12/08
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: "J. Clarke" <jclarke...@cox.net>
: OK, you've lost me. I was assuming that you were basing your
: objection to the use of Rigel and Deneb on their relatively short
: lives, which was calculated assuming that they were powered by
: hydrogen fusion and that the reaction released a certain quantity of
: energy per unit mass.
:
: If that is not your objection, then what is? I don't see how the mass
: of the star, per se, is an issue.

Gene's point (iiui) is that there is experimental support that the
luminosity relationship holds for stars other than Rigel and Deneb.
Hence, I'm guessing your point is "well, maybe they thought Rigel and
Deneb weren't powered by the same processes as the stars for which
experimental support existed".

These two points aren't exactly in conflict; but the fact that all the
stars they had independent confirmation for seemed to be powered by
hydrogen fusion means the presumption that some weren't is on shakier
ground than if the theory had no data at all, or had significant exceptions.


Wayne Throop thr...@sheol.org http://sheol.org/throopw

Sea Wasp (Ryk E. Spoor)

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Oct 12, 2008, 10:02:42 PM10/12/08
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Wayne Throop wrote:
> : "J. Clarke" <jclarke...@cox.net>
> : OK, you've lost me. I was assuming that you were basing your
> : objection to the use of Rigel and Deneb on their relatively short
> : lives, which was calculated assuming that they were powered by
> : hydrogen fusion and that the reaction released a certain quantity of
> : energy per unit mass.
> :
> : If that is not your objection, then what is? I don't see how the mass
> : of the star, per se, is an issue.
>
> Gene's point (iiui) is that there is experimental support that the
> luminosity relationship holds for stars other than Rigel and Deneb.
> Hence, I'm guessing your point is "well, maybe they thought Rigel and
> Deneb weren't powered by the same processes as the stars for which
> experimental support existed".

As I understood it, he was saying "perhaps it would turn out those
models were wrong, or missing some critical elements, or that life's
evolution proceeded faster than we thought in many cases, so that even
very short-lived stars could have life-bearing planets, or might not be
as short-lived as we thought."


--
Sea Wasp
/^\
;;;
Live Journal: http://seawasp.livejournal.com

Gene

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Oct 12, 2008, 10:44:16 PM10/12/08
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"J. Clarke" <jclarke...@cox.net> rote in
news:gcu4q...@news3.newsguy.com:

> If that is not your objection, then what is? I don't see how the mass
> of the star, per se, is an issue.

If you know the mass some stars and their luminosity, you can do a log-log
plot of the results and there is the mass-luminosity relationship empirically
determined, without appeal to theory.

Gene

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Oct 12, 2008, 10:55:29 PM10/12/08
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thr...@sheol.org (Wayne Throop) rote in news:12238...@sheol.org:

> These two points aren't exactly in conflict; but the fact that all the
> stars they had independent confirmation for seemed to be powered by
> hydrogen fusion means the presumption that some weren't is on shakier
> ground than if the theory had no data at all, or had significant
exceptions.

Even without knowing that, if we assume the total energy available to a star
is proportional to its mass, then knowing the luminosity of a main sequence
star is proportional to the 3.5 power of irts mass shows heavier stars must
last for a far shorter time.

Wayne Throop

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Oct 12, 2008, 10:48:45 PM10/12/08
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: "Sea Wasp (Ryk E. Spoor)" <sea...@sgeinc.invalid.com>
: As I understood it, he was saying "perhaps it would turn out those
: models were wrong, or missing some critical elements, or that life's
: evolution proceeded faster than we thought in many cases, so that even
: very short-lived stars could have life-bearing planets, or might not be
: as short-lived as we thought."

That's a couple of sub-contexts back, but yes.
The context immediately at hand is

From: "J. Clarke" <jclarke...@cox.net>
I was assuming that you were basing your objection to the use of
Rigel and Deneb on their relatively short lives, which was
calculated assuming that they were powered by hydrogen fusion and
that the reaction released a certain quantity of energy per unit mass.

and that's not quite the assumption being made. The assumption being
made was that a relationship which holds for other stars holds for them.
That's not the same thing as saying a specific power source was assumed,
and lumniosity calculated by theory alone.

James Nicoll

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Oct 12, 2008, 11:24:54 PM10/12/08
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In article <Xns9B35897EE6EE2ge...@207.115.33.102>,

The second. They were just using the names of the stars whose
names they knew and named stars have a very high fraction of high-mass,
short lifespan stars.

You can narrow down when Poul Anderson first learned about this
issue by looking at the editions of THE ENEMY STARS. The early editions
(1959ish) have human colonies on worlds orbiting high mass, named stars
and gravity propagates instantaneously. By the 1979 Berkley MMPK reprint,
the stars have been changed, the FTL communications use tachyons and there's
one of those Poul intros he wrote in the 1970s.
--
http://www.livejournal.com/users/james_nicoll
http://www.cafepress.com/jdnicoll (For all your "The problem with
defending the English language [...]" T-shirt, cup and tote-bag needs)

J. Clarke

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Oct 13, 2008, 12:30:08 AM10/13/08
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So what? So we know that there is a mass-luminosity relationship.
Big deal.

J. Clarke

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Oct 13, 2008, 12:28:24 AM10/13/08
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And how long does a star have to last for sentient life to evolve?
Suppose that the process by which stars are powered yields a lifetime,
say, a thousand times longer than current estimates. Then Rigel and
Deneb could have been around as long as we currently estimate that the
Sun has been around.

Wayne Throop

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Oct 13, 2008, 12:38:22 AM10/13/08
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: "J. Clarke" <jclarke...@cox.net>
: Suppose that the process by which stars are powered yields a lifetime,
: say, a thousand times longer than current estimates.

Plausible lifetimes ranged *downwards* from that provided by fusion.
Sure, you could posit one, but then that answers the original question
via the "simply being ignored" case.

FWIW, back to the original question, "Was this simply being ignored as
so much was ignored, or had the news not reached most sci-fi authors?",
I expect the answer is along the lines of "a little of each".

Gene

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Oct 13, 2008, 1:01:16 AM10/13/08
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"J. Clarke" <jclarke...@cox.net> rote in
news:gcuit...@news6.newsguy.com:

* And how long does a star have to last for sentient life to evolve?

It took us billions of years just to get to the Cambrian explosion.

> Suppose that the process by which stars are powered yields a lifetime,
> say, a thousand times longer than current estimates. Then Rigel and
> Deneb could have been around as long as we currently estimate that the
> Sun has been around.

It really can't; you run into E=Mc^2 problems. You are already releasing
around 1% of the mass, a hundred times that and you are getting all of it
converted to energy.


J. Clarke

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Oct 13, 2008, 12:31:31 AM10/13/08
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Uh, Wayne, the relationship between luminosity and mass is empirical
and it alone tells us exactly nothing about the ages of stars. To get
the ages one must make assumptions about the process by which they are
powered. The standard assumption, and the one on which Eddington's
estimate is based, is that they are powered by hydrogen fusion. If in
fact it turns out that stars are not powered by hydrogen fusion but by
some other process then that estimate becomes invalid.

Gene

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Oct 13, 2008, 1:07:40 AM10/13/08
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"J. Clarke" <jclarke...@cox.net> rote in
news:gcuit...@news6.newsguy.com:

>> If you know the mass some stars and their luminosity, you can do a
>> log-log plot of the results and there is the mass-luminosity
>> relationship empirically determined, without appeal to theory.
>
> So what? So we know that there is a mass-luminosity relationship.
> Big deal.

Very little in addition is now needed to show stars like Rigel cant last very
long. The exact details of how energy is being obtained don't really matter
in light of the fact that if you aren't fusing hydrogen to helium you are
presumably getting even less energy than that would allow, and hence a lesser
lifetime,

J. Clarke

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Oct 13, 2008, 1:46:59 AM10/13/08
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Gene wrote:
> "J. Clarke" <jclarke...@cox.net> rote in
> news:gcuit...@news6.newsguy.com:
>
> * And how long does a star have to last for sentient life to evolve?
>
> It took us billions of years just to get to the Cambrian explosion.

And we know that this amount of time is _required_ because?

>> Suppose that the process by which stars are powered yields a
>> lifetime, say, a thousand times longer than current estimates.
>> Then
>> Rigel and Deneb could have been around as long as we currently
>> estimate that the Sun has been around.
>
> It really can't; you run into E=Mc^2 problems. You are already
> releasing around 1% of the mass, a hundred times that and you are
> getting all of it converted to energy.

So what process powered the Big Bang and why can that process not
power stars?

J. Clarke

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Oct 13, 2008, 1:36:03 AM10/13/08
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Oh ye of little imagination. As an exercise, try to think of three
plausible (story-plausible, not Physical Review-plausible) ways in
which stars could be powered that would provide more energy than
fusion.

J. Clarke

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Oct 13, 2008, 1:40:48 AM10/13/08
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Wayne Throop wrote:
>> "J. Clarke" <jclarke...@cox.net>
>> Suppose that the process by which stars are powered yields a
>> lifetime, say, a thousand times longer than current estimates.
>
> Plausible lifetimes ranged *downwards* from that provided by fusion.
> Sure, you could posit one, but then that answers the original
> question
> via the "simply being ignored" case.

*downwards* based on what assumptions?

Gene

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Oct 13, 2008, 2:40:41 AM10/13/08
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"J. Clarke" <jclarke...@cox.net> rote in
news:gcuo5...@news2.newsguy.com:

>> It really can't; you run into E=Mc^2 problems. You are already
>> releasing around 1% of the mass, a hundred times that and you are
>> getting all of it converted to energy.
>
> So what process powered the Big Bang and why can that process not
> power stars?

It's possible stars are powered by the combustion of pixie dust. However,
postulating that takes us rather far from the original question, which was
about actual astrophysics and its relationship top science fiction.

Gene

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Oct 13, 2008, 2:45:44 AM10/13/08
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"J. Clarke" <jclarke...@cox.net> rote in news:gcuo551lv9
@news2.newsguy.com:

> Oh ye of little imagination. As an exercise, try to think of three
> plausible (story-plausible, not Physical Review-plausible) ways in
> which stars could be powered that would provide more energy than
> fusion.

1. Pixie dust
2. Hot air channeled from science fiction fans
3. Hot air channeled from James P. Hogan

Wayne Throop

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Oct 13, 2008, 2:23:30 AM10/13/08
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: "J. Clarke" <jclarke...@cox.net>
: Uh, Wayne, the relationship between luminosity and mass is empirical
: and it alone tells us exactly nothing about the ages of stars. To get
: the ages one must make assumptions about the process by which they are
: powered.

If you assume it's total conversion, you get a lifetime only a hundred
times longer than that for hydrogen. Of course, the *total* lifetime
of the star could be quite long, since one could presume the luminoslity
would go down as the mass gets consumed. But the llifetime *at* *high*
*luminosity* is still quite a bit shorter than a hundred times as long.
Luminosity falls to hearly half once you've used up 18% of the total,
so that's only 10 or 20 times the lifetime you'd get from hydrogen.
And you aren't getting stable conditions to evolve in for that time.

So, no, assuming it's some other energy-producing process
doesn't help much.

If you assume you get the energy from magic fairies, that'd work.
But again, that's just a subcase of "ignoring it".

Well, there's also the "gotten by galactic electric discarge" theory
of the "electric universe" crowd, but that doesn't fit with the
luminosity related to mass, so one might as well blame the fairies.

And of course, nowdays you could call blame the *zero* *point* fairies
to sound all scientific-like, but that seems an unlikely ploy for
back then.


"They used Raoul Mitgong, but he didn't help much."

--- Harlan Ellison

Wayne Throop

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Oct 13, 2008, 2:47:16 AM10/13/08
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: "J. Clarke" <jclarke...@cox.net>
: *downwards* based on what assumptions?

On the "assumption" (as in, known fact at that time) that hydrogen fusion
is the most energyetic available. And the fact that even with total
conversion, you don't get more than an order of magnitude improvement,
which isn't nearly enough.

If you want to assume the energy isn't limited by E=mc^2,
that's just a subcase of "ignoring it".

Bill Snyder

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Oct 13, 2008, 3:15:03 AM10/13/08
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Pish tush. #3 would clearly require having the inner edge of the
life zone for this system somewhere in the Oort Cloud.

--
Bill Snyder [This space unintentionally left blank]

Wayne Throop

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Oct 13, 2008, 2:51:03 AM10/13/08
to
: "J. Clarke" <jclarke...@cox.net>
: Oh ye of little imagination. As an exercise, try to think of three
: plausible (story-plausible, not Physical Review-plausible) ways in
: which stars could be powered that would provide more energy than
: fusion.

The category proposed for this in the original question is "ignoring it".
Hydrogen fusion is the most energetic reaction, this fact was known then,
and if you go to total conversion for no particular reason, you don't
get more than about an order of magnitude improvement in times, which
is still way out of the ballpark.

So yes, this is fiction and the story gets to say anything it wants.
But if you assume such high-luminosity stars last for a billion years,
they pretty much fall into the category "ignoring it".


"If the British Empire and its Commonwealth last for a thousand
years, men will still say, 'This was their finest hour'."

--- Winston Churchill

Wayne Throop

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Oct 13, 2008, 3:30:57 AM10/13/08
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: "J. Clarke" <jclarke...@cox.net>
: So what process powered the Big Bang and why can that process not
: power stars?

Inflation. http://en.wikipedia.org/wiki/Cosmic_inflation
Details of which were completely unknown at the time.
If stars were powered by it, it would be noticeable
(as opposed to mostly-unknown as now).

And, if the energy comes from the magic inflationary energy fairies,
it becomes odd that luminosity would be related to mass.

So again, this falls into the "ignoring it" category.

J. Clarke

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Oct 13, 2008, 8:32:55 AM10/13/08
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Wayne Throop wrote:
>> "J. Clarke" <jclarke...@cox.net>
>> Oh ye of little imagination. As an exercise, try to think of three
>> plausible (story-plausible, not Physical Review-plausible) ways in
>> which stars could be powered that would provide more energy than
>> fusion.
>
> The category proposed for this in the original question is "ignoring
> it". Hydrogen fusion is the most energetic reaction, this fact was
> known then, and if you go to total conversion for no particular
> reason, you don't get more than about an order of magnitude
> improvement in times, which
> is still way out of the ballpark.

Uh, hydrogen fusion is more energetic than matter-antimatter
annihilation? Do tell.

And do tell us where the energy came from for the Big Bang.

> So yes, this is fiction and the story gets to say anything it wants.
> But if you assume such high-luminosity stars last for a billion
> years,
> they pretty much fall into the category "ignoring it".

Or having more imagination than the participants in this thread.

J. Clarke

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Oct 13, 2008, 8:33:21 AM10/13/08
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Yep. No imagination. Or far less knowledge of physics than you think
you have.

J. Clarke

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Oct 13, 2008, 8:44:46 AM10/13/08
to
Wayne Throop wrote:
>> "J. Clarke" <jclarke...@cox.net>
>> Uh, Wayne, the relationship between luminosity and mass is
>> empirical
>> and it alone tells us exactly nothing about the ages of stars. To
>> get the ages one must make assumptions about the process by which
>> they are powered.
>
> If you assume it's total conversion, you get a lifetime only a
> hundred
> times longer than that for hydrogen. Of course, the *total*
> lifetime
> of the star could be quite long, since one could presume the
> luminoslity would go down as the mass gets consumed. But the
> llifetime *at* *high* *luminosity* is still quite a bit shorter than
> a hundred times as long. Luminosity falls to hearly half once you've
> used up 18% of the total, so that's only 10 or 20 times the lifetime
> you'd get from hydrogen.

Who has determined that luminosity falls to nearly half once you've
used up 18 percent of the total if the energy source is not fusion?
You're making assumptions here again that may not be valid.

> And you aren't getting stable conditions to evolve in for that time.

Uh, why are "stable conditions" needed? Slowly changing should be
good enough. The luminosity of the Sun has increased by something
like 30 percent since it formed.

> So, no, assuming it's some other energy-producing process
> doesn't help much.

If you assume that other than the different process the behavior of
stars is exactly as it would be for fusion . . .

> If you assume you get the energy from magic fairies, that'd work.
> But again, that's just a subcase of "ignoring it".
>
> Well, there's also the "gotten by galactic electric discarge" theory
> of the "electric universe" crowd, but that doesn't fit with the
> luminosity related to mass, so one might as well blame the fairies.
>
> And of course, nowdays you could call blame the *zero* *point*
> fairies
> to sound all scientific-like, but that seems an unlikely ploy for
> back then.

Try some others.

J. Clarke

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Oct 13, 2008, 8:46:53 AM10/13/08
to
Wayne Throop wrote:
>> "J. Clarke" <jclarke...@cox.net>
>> *downwards* based on what assumptions?
>
> On the "assumption" (as in, known fact at that time) that hydrogen
> fusion is the most energyetic available. And the fact that even
> with
> total conversion, you don't get more than an order of magnitude
> improvement, which isn't nearly enough.
>
> If you want to assume the energy isn't limited by E=mc^2,
> that's just a subcase of "ignoring it".

Ten thousand years from now the notion that hydrogen fusion is "the
most energetic available" may seem as quaint as the notion that coal
is "the most energetic available" seems to us.

Further we already know of more energetic reactions, so your continued
assertion that fusion is "the most energetic available" is puzzling.

J. Clarke

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Oct 13, 2008, 8:54:09 AM10/13/08
to
Wayne Throop wrote:
>> "J. Clarke" <jclarke...@cox.net>
>> So what process powered the Big Bang and why can that process not
>> power stars?
>
> Inflation. http://en.wikipedia.org/wiki/Cosmic_inflation

Read that article carefully.


> Details of which were completely unknown at the time.
> If stars were powered by it, it would be noticeable
> (as opposed to mostly-unknown as now).

Details of which are still unknown. How would it be "noticeable"?
Give us a test since you assert that there is one. Do tell us about
the experiments in which you observed the properties of the inflaton
particle.

> And, if the energy comes from the magic inflationary energy fairies,
> it becomes odd that luminosity would be related to mass.

Why?

> So again, this falls into the "ignoring it" category.

So I guess that the physicists are just "ignorinig it" when they can't
come up with a mechanism other than "inflatons" to power the big bang.

Sea Wasp (Ryk E. Spoor)

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Oct 13, 2008, 10:55:19 AM10/13/08
to
J. Clarke wrote:
> Wayne Throop wrote:
>>> "J. Clarke" <jclarke...@cox.net>
>>> *downwards* based on what assumptions?
>> On the "assumption" (as in, known fact at that time) that hydrogen
>> fusion is the most energyetic available. And the fact that even
>> with
>> total conversion, you don't get more than an order of magnitude
>> improvement, which isn't nearly enough.
>>
>> If you want to assume the energy isn't limited by E=mc^2,
>> that's just a subcase of "ignoring it".
>
> Ten thousand years from now the notion that hydrogen fusion is "the
> most energetic available" may seem as quaint as the notion that coal
> is "the most energetic available" seems to us.

Not for a star. I'm as much a fan of Get-To-It space opera as the next
person, but this is an area we know enough about that the idea that
ANYTHING other than fusion (and, for the most part, hydrogen-hydrogen
fusion) is powering them is a HUGE stretch -- basically tantamount to
"ignoring it", as Gene says.

I will cheerfully ignore physics whenever it gets in my story's way, as
long as I do so CONSISTENTLY, but I won't deny that this is exactly what
I'm doing.

>
> Further we already know of more energetic reactions,

Not any which could reasonably be postulated as the main drivers for
star power. H-H fusion is the most energetic reaction reasonably able to
be postulated for running most stars.


--
Sea Wasp
/^\
;;;
Live Journal: http://seawasp.livejournal.com

Wayne Throop

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Oct 13, 2008, 11:10:35 AM10/13/08
to
: "J. Clarke" <jclarke...@cox.net>
: Who has determined that luminosity falls to nearly half once you've
: used up 18 percent of the total if the energy source is not fusion?

Um. You recall the mass-luminosity relationship? You're emitting E,
and hence by E=mc^2 you are losing m, and with lower m you get
lower luminosity, which is a given of the scenario (ie, the
mass/luminosity relationship is experimentally determined; it's why
we were looking for an energy source in the first place).

This is not a significant issue for hydrogen fusion, since it only
loses 1 percent of the m before running out of E, but for any process
that yields *more* energy than hydrogen fusion, it becomes an issue.

: Uh, why are "stable conditions" needed?

Because a given planet would pass through the entire Goldilox Zone
way too fast (or rather, the GZ would pass past it). Unless it were
"spiraling in" towards the sun, and a) that still falls into "ignoring
it", and b) it still, at max, gets you two orders of magnitude, not
three as you proposed.

: Try some others.

Why? The question was, were SF authors unaware of the probem
mass/luminosity posed, or did they ignore it. You're trying to wiggle
out of the fact that there's a problem, but in suggesting "they could
come up with zany ways to get the energy", you are simply answering the
original question by "they knew, and ignored it". Coming up with more
zany proposals won't change that. So what are these "others" in aid of?

J. Clarke

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Oct 13, 2008, 11:25:52 AM10/13/08
to
Sea Wasp (Ryk E. Spoor) wrote:
> J. Clarke wrote:
>> Wayne Throop wrote:
>>>> "J. Clarke" <jclarke...@cox.net>
>>>> *downwards* based on what assumptions?
>>> On the "assumption" (as in, known fact at that time) that hydrogen
>>> fusion is the most energyetic available. And the fact that even
>>> with
>>> total conversion, you don't get more than an order of magnitude
>>> improvement, which isn't nearly enough.
>>>
>>> If you want to assume the energy isn't limited by E=mc^2,
>>> that's just a subcase of "ignoring it".
>>
>> Ten thousand years from now the notion that hydrogen fusion is "the
>> most energetic available" may seem as quaint as the notion that
>> coal
>> is "the most energetic available" seems to us.
>
> Not for a star. I'm as much a fan of Get-To-It space opera as the
> next
> person, but this is an area we know enough about that the idea that
> ANYTHING other than fusion (and, for the most part,
> hydrogen-hydrogen
> fusion) is powering them is a HUGE stretch -- basically tantamount
> to
> "ignoring it", as Gene says.

We have good reason to believe that fusion is the power source, now,
today, but the reason was less well established in the "golden age"
and there's clearly something wrong with our model--either something
is going on besides fusion, or we don't understand fusion as well as
we thought we did, or we don't understand neutrinos as well as we
thought we did.

In any case, "ignoring it" means just that, coming up with a plausible
rationalization is not "ignoring it".

> I will cheerfully ignore physics whenever it gets in my story's way,
> as long as I do so CONSISTENTLY, but I won't deny that this is
> exactly what I'm doing.
>
>>
>> Further we already know of more energetic reactions,
>
> Not any which could reasonably be postulated as the main drivers for
> star power. H-H fusion is the most energetic reaction reasonably
> able
> to be postulated for running most stars.

Actually it's the most energetic fuel that we can come up with that
seems to be present in stars. This is different from the most
energetic reaction "reaonably able to be postulated" for purposes of
writing story.