Fusion? Fusion? We don't need no steeenking Fusion
Wim Lewis
James Nicoll <jdni...@panix.com> wrote:
>In article <9oq62l$a71$1...@bubba.NMSU.Edu>,
>William Baird <wba...@acca.nmsu.edu> wrote:
>>James Nicoll <jdni...@panix.com> wrote:
>>> Note that the ftttttt may well make all your hair fall out
>>> while evaporating your city depending on the size of the BH, so
>>> don't do this without a permit.
>>
>>Do I smell a nuclear weapon replacement, folks?
>>
>>How much energy would it take to make one of these guys?
>>
> More than you'll get back out.
Well, all of the energy you put in is going to come out. I guess that the
particle accelerator you use to create them may not be very energy-efficient,
though...
On the other hand, if it's big enough you could try to feed it matter
after creating it, and this matter will mostly come out as energy later.
> This thing has even worse storage and maintainance issues
>than nuclear weapons do, as well.
Mm, yes, quite.
Maybe you could use them in a beam-type weapon --- create them on-demand,
when the gun is fired. Feed them mass while accelerating them and adjusting
their trajectory. Arrange the final mass (lifetime) and speed so that they
go fffftttt inside the target. You would need absurdly accurate accelerators
to do this but I don't see a reason why it would be impossible in *theory*.
(insert disclaimer here).
This would be an interesting weapon; it would release a lot of energy
at a particular distance, with a relatively sharp cutoff on the distant
side, but a much more gradual cutoff on the near side (extending
all the way back to the gun).
It would probably have a number of non-weapon uses too, but I can't think of
them offhand. Maybe you could use them to heat the interior of an object
without doing more than a little bit of damage to its outsides. I assume
that a small, uncharged black hole would not interact very much with
the matter it's passing through.
(The practicality of this depends on how much energy is in the ffffttt ---
as I understand it, the energy released in the last, say, 10 nanoseconds
should be a constant, regardless of the original mass of the hole. The
thread originated with speculation that BHs might be easier to create if
gravity starts acting along an inverse-cube at short distances as predicted
by some theories, and I assume that would affect the size of the ffffttt.
Might it start acting as r^-4 at even smaller scales, all the way up to r^-11
(or whatever thenumber of dimensions is) at the very end of it all?)
--
Wim Lewis <wi...@hhhh.org>, Seattle, WA, USA. PGP keyID 27F772C1
My ambition is to have all [my] arguments seem annoyingly plausible -Joe Slater
Mark Atwood
>
> This would be an interesting weapon; it would release a lot of energy
> at a particular distance, with a relatively sharp cutoff on the distant
> side, but a much more gradual cutoff on the near side (extending
> all the way back to the gun).
Sort of like a Fed phaser then. Power to blow apart rocks, can heat
rocks from the inside out, without frying the wielder's hand, a
perfectly columated beam of potentially titanic energy density, and
still has a relatively limited range....
--
Mark Atwood | I'm wearing black only until I find something darker.
m...@pobox.com | http://www.pobox.com/~mra
Aaron Bergman
William Mc Hale <wmc...@umbc7.umbc.edu> wrote:
[Hunh. Must have missed this one.]
> There is a certain irony in the fact that we might be able to create black
> holes long before we have stable fusion. If certain versions of string
> theory are correct gravity's strength will switch over from the inverse
> square law to the inverse cube law once you get two objects close enough
> together. If that is right, the next generation of colliders should be
> able to create black holes with very tiny masses.
This isn't quite correct. Here's the basic story. String theory predicts
that the world has 10 dimensions (string theory has since been subsumed
in a poorly understood theory called M-theory that lives in 11
dimensions.). Unfortunately, we don't see 10 dimensions, so that
presents a bit of a problem. The answer is that the other dimensions
must be hidden from us somehow.
So, how can we measure the number of dimensions? If we have a force that
obeys Gauss's law, then, in D dimensions, the force between two
particles scales as r^-(D-2). If the extra dimensions were curled up
really small, then, at large scales, the force doesn't really have
anywhere to go in those dimensions, so the 'D' in the exponent above is
only the number of large dimensions. You can sort of picture this by
thinking about two particles on a really long cylinder. If the two
particles are close to each other, it looks like they live in two
dimensions and the lines of force can spread out. However, if the two
particles are really far away from each other, the lines of force can
only go along the length of the cylinder and the spreading out that they
do along the circumference is negligible in comparison.
So, this exponent has been measured up to really small distances for
electromagnetism. Just as an example, all of chemistry would be
different if the exponent were small at the atomic scale. So, for years,
people thought that these extra dimensions had to be really really
small, probably around the Planck scale since that's the natural scale
associated with quantum gravity. Actually, Antoniadis around 1990 or so
talked about extra dimensions larger than this, but those papers aren't
online, so I'm not going to talk about them.
Anyways, in the last decade or so, string theory has become much better
understood. One of the major new things is that, in addition to strings,
it contains other objects of various dimensions that a string can end
on, callled D-branes. Because the strings end on this D-brane, instead
of creating all the forces we know and love throughout all of spacetime,
the forces only live on the D-brane. People soon noticed that this means
that we could live on one of these branes. This is known as a braneworld
scenario. In this situation, the above test doesn't tell us the size of
the extra-dimensions because we could be living on a 3+1 dimensional
brane in the ten dimensional spacetime. We're stuck on this
hypersurface, and we can't get off.
Actually, I lied a bit. Not all of the forces are confined to live on
the brane. Gravity is carried by closed strings which have no end, so
they obviously aren't forced to live on the D-brane. Thus, people
started looking for tests of the inverse square law for gravity. This is
a hard experiment to do, and the best results were around a millimeter
or so. They've since been lowered to a 100 microns or so, but that's
still quite large. As a side note, Lisa Randall and Raman Sundrum showed
how one can even localize gravity to the brane allowed the extra
dimensions to actually be infinite, but that's not really what we're
going after here, so we'll ignore them, too.
Once we have these extra dimensions, we have to ask ourselves what do we
really mean by the Planck scale. The Planck scale is just something one
gets with units of energy formed out of G, the gravitational constant,
h-bar, Planck's constant divided by 2pi, and c, the speed of light. But,
if these extra dimensions are there, the G that we measure is no longer
the "real" G. Instead, there's a factor of the volume of those extra
dimensions in there (related to the fact that the field lines do spread
out in them.). If that were small, ie, of order 1, then that wouldn't be
a problem. But, if these extra dimensions are big, then, suddenly, the
Planck scale isn't what we thought it was. In fact, it could be much
smaller.
We've got some pretty decent accelerators right now, and they haven't
seen any of these extra dimensions yet, so, we do have a lower bound
atleast in this scenario (there are other scenarios which get it down to
10^-3 eV or so which is a somewhat interesting number because it's
actually the measured value of the cosmological constant give or take a
bit.) But, we can still imagine that quantum gravity might just be
around the corner. There are some reasons to like this scenario. One of
the big problems with physics we actually think we understand (unlike
string theory) is that the Higgs mass should really be at the quantum
gravity scale. It's only a remarkable coincidence that it's not.
Physicists don't like coincidences, so this is considered a problem. Of
course it's really a bit more complicated than that, but that really is
the essence. So, one way to get rid of this hierarchy problem is to,
well, get rid of it. Instead of having some huge Planck scale, if it's
just the weak scale, the problem goes away. That's kind of cool.
There are reasons not to believe this, too, and going into all the ins
and outs of it isn't really possible here. However, the neat thing is
that, if this were true, we could see quantum gravity in the next round
of accelerators or so. Instead of some vast particle desert above the
weak scale as some expected, there would, instead, be all the goodies of
quantum gravity. So, people have started to explore what might happen.
Recently, Steve Giddings and Scott Thomas wrote that one might produce
black holes in the colliders and what the consequences of that would be.
The paper is available online at
<http://xxx.lanl.gov/abs/hep-ph/0106219>. Savas Dimopoulos and Greg
Landsberg have similar ideas <http://xxx.lanl.gov/abs/hep-ph/0106295>.
Needless to say, it would be quite cool if all this were true. I'm not
really sure I believe it, though. It makes some pictures that are quite
nice a bit more complicated. Who knows, though. Maybe we'll see when LHC
turns on.
Aaron
Joe Slater
>As a side note, Lisa Randall and Raman Sundrum showed
>how one can even localize gravity to the brane allowed the extra
>dimensions to actually be infinite,
My brane hurts.
jds
--
Joe Slater was but a low-grade paranoiac, whose fantastic notions must
have come from the crude hereditary folk-tales which circulated in even
the most decadent of communities.
_Beyond the Wall of Sleep_ by H P Lovecraft
Aaron Bergman
Joe Slater <joeDEL...@yoyo.cc.monash.edu.au> wrote:
> Aaron Bergman <aber...@princeton.edu> wrote:
> >As a side note, Lisa Randall and Raman Sundrum showed
> >how one can even localize gravity to the brane allowed the extra
> >dimensions to actually be infinite,
>
> My brane hurts.
Believe me, all the jokes have been made before. Please don't.
Anyways, the word comes from membrane. A membrane is two (well, 2+1,
really, because it also extends in time. We drive the mathematicians
nuts that way.) dimensional and is called a 2-brane. A p-dimensional
(really p+1) thingie is called a, well, take a guess. And the term is
quite common in the literature. Physicists have bizarre senses of humor.
Actual recent paper titles:
Raiders of the Lost AdS
Brane New World
Invasion of the Giant Gravitons from Anti-de Sitter Space
*-Trek III: The Search for Ramond-Ramond Couplings
*-Wars Episode I: The Phantom Anomaly
How Bob Laughlin Tamed the Giant Graviton from Taub-NUT space
Don't Panic! Closed String Tachyons in ALE Spacetimes
The Good, the Bad and the Naked
Those are just off the top of my head.
Aaron
Neil Barnes
>wi...@underhill.hhhh.org (Wim Lewis) writes:
>>
>> This would be an interesting weapon; it would release a lot of energy
>> at a particular distance, with a relatively sharp cutoff on the distant
>> side, but a much more gradual cutoff on the near side (extending
>> all the way back to the gun).
>
>Sort of like a Fed phaser then. Power to blow apart rocks, can heat
>rocks from the inside out, without frying the wielder's hand, a
>perfectly columated beam of potentially titanic energy density, and
>still has a relatively limited range....
>
And still slow enough to dodge out of its way!
Maybe we need to use Q-type helices to contain the backblast?
--
I have a quantum car. Every time I look at the speedometer I get lost...
barnacle
http://www.nailed-barnacle.co.uk
Bertil Jonell
Wim Lewis <wi...@underhill.hhhh.org> wrote:
>Maybe you could use them in a beam-type weapon --- create them on-demand,
>when the gun is fired. Feed them mass while accelerating them and adjusting
>their trajectory. Arrange the final mass (lifetime) and speed so that they
>go fffftttt inside the target. You would need absurdly accurate accelerators
>to do this but I don't see a reason why it would be impossible in *theory*.
>(insert disclaimer here).
Donaldson's "Matter Cannon" worked something like that except it created
the hole in the target: Some doublespeak about "interference between different
beams creates an energy density high enough to not only create matter, but
make that matter into a singularity" IIRC.
> Wim Lewis <wi...@hhhh.org>, Seattle, WA, USA. PGP keyID 27F772C1
-bertil-
--
"It can be shown that for any nutty theory, beyond-the-fringe political view or
strange religion there exists a proponent on the Net. The proof is left as an
exercise for your kill-file."
Sea Wasp
> Actual recent paper titles:
>
> Raiders of the Lost AdS
> Brane New World
> Invasion of the Giant Gravitons from Anti-de Sitter Space
> *-Trek III: The Search for Ramond-Ramond Couplings
> *-Wars Episode I: The Phantom Anomaly
> How Bob Laughlin Tamed the Giant Graviton from Taub-NUT space
> Don't Panic! Closed String Tachyons in ALE Spacetimes
> The Good, the Bad and the Naked
>
> Those are just off the top of my head.
Correct me if I'm wrong, but I seem to recall that in my youth even
SUBMITTING such a title for consideration would have had your paper
bounced back to you so fast that you could have done experiments with
it to verify relativity.
--
Sea Wasp http://www.wizvax.net/seawasp/index.htm
/^\
;;; _Morgantown: The Jason Wood Chronicles_, at
http://www.hyperbooks.com/catalog/20040.html
Aaron Bergman
wrote:
> Aaron Bergman wrote:
>
> > Actual recent paper titles:
> >
> > Raiders of the Lost AdS
> > Brane New World
> > Invasion of the Giant Gravitons from Anti-de Sitter Space
> > *-Trek III: The Search for Ramond-Ramond Couplings
> > *-Wars Episode I: The Phantom Anomaly
> > How Bob Laughlin Tamed the Giant Graviton from Taub-NUT space
> > Don't Panic! Closed String Tachyons in ALE Spacetimes
> > The Good, the Bad and the Naked
> >
> > Those are just off the top of my head.
>
> Correct me if I'm wrong, but I seem to recall that in my youth even
> SUBMITTING such a title for consideration would have had your paper
> bounced back to you so fast that you could have done experiments with
> it to verify relativity.
I certainly can't tell you things about your youth, but some of the
names on those papers are some of the best people in the field. The
second one is Hawking, or example. Two of them are from Lenny Susskind.
The second last is from Joe Polchinski and Eva Silverstein. The last one
is Steve Gubser.
Aaron
Sea Wasp
>
> In article <3BB1FA...@wizvax.net>, Sea Wasp <sea...@wizvax.net>
> wrote:
>
> > Aaron Bergman wrote:
> >
> > > Actual recent paper titles:
> > >
> > > Raiders of the Lost AdS
> > > Brane New World
> > > Invasion of the Giant Gravitons from Anti-de Sitter Space
> > > *-Trek III: The Search for Ramond-Ramond Couplings
> > > *-Wars Episode I: The Phantom Anomaly
> > > How Bob Laughlin Tamed the Giant Graviton from Taub-NUT space
> > > Don't Panic! Closed String Tachyons in ALE Spacetimes
> > > The Good, the Bad and the Naked
> > >
> > > Those are just off the top of my head.
> >
> > Correct me if I'm wrong, but I seem to recall that in my youth even
> > SUBMITTING such a title for consideration would have had your paper
> > bounced back to you so fast that you could have done experiments with
> > it to verify relativity.
>
> I certainly can't tell you things about your youth, but some of the
> names on those papers are some of the best people in the field.
That wasn't what I was asking. I didn't doubt that they were from
competent researchers. It was more a comment of "I swear that in the
old days you couldn't have DONE that..."
I.e., in the old days scholarship was serious business, no time for
funny stuff. (one reason Feynman used to cause twitches in the
academic community)
Thomas Palm
> I.e., in the old days scholarship was serious business, no time for
> funny stuff. (one reason Feynman used to cause twitches in the
> academic community)
Well, there is the paper by Alpher and Gamow about nucleosynthesis where
Gamow invited Bethe to be a coauthor just so that the authors would
(almost) be abc in greek.
Then there is the author (I have forgotten who) who put his cat
as second author on a paper. He had written "we" all over and
were told that journal didn't accept that if there was only one
author. Since this was before wordprocessors he thought it was
to much work to change the manuscript. He even sent out reprints
with his own signature and a pawprint. (Supposedly the cat was
subsequently almost invited as a speaker on a conference.)
You just had to be a bit more subtle in your humor back then.
William T. Hyde
> Aaron Bergman wrote:
>
> > Actual recent paper titles:
> >
> > Raiders of the Lost AdS
> > Brane New World
> > Invasion of the Giant Gravitons from Anti-de Sitter Space
> > *-Trek III: The Search for Ramond-Ramond Couplings
> > *-Wars Episode I: The Phantom Anomaly
> > How Bob Laughlin Tamed the Giant Graviton from Taub-NUT space
> > Don't Panic! Closed String Tachyons in ALE Spacetimes
> > The Good, the Bad and the Naked
> >
> > Those are just off the top of my head.
>
In 1976 a seminal paper was entitled:
"Variations in the earth's orbit: Pacemaker of
the ice ages"
Nothing unusual there, but a recent paper on the
harmonics of orbital variation was entitled
"The Pacemaker always rings twice".
William Hyde
EOS Department
Duke University
David Given
wi...@underhill.hhhh.org (Wim Lewis) writes:
[...]
> (The practicality of this depends on how much energy is in the ffffttt ---
> as I understand it, the energy released in the last, say, 10 nanoseconds
> should be a constant, regardless of the original mass of the hole. The
> thread originated with speculation that BHs might be easier to create if
> gravity starts acting along an inverse-cube at short distances as predicted
> by some theories, and I assume that would affect the size of the ffffttt.
> Might it start acting as r^-4 at even smaller scales, all the way up to r^-11
> (or whatever thenumber of dimensions is) at the very end of it all?)
I remember hearing somewhere that a black hole going phht in the vicinity
of Earth will, in the last second of its life, emit enough energy to make
most of the Earth just disappear, and blight the Sun sufficiently to knock
it off the Main Trunk[1]. Has anyone got the energy emission formula
handy?
[1] Aaargh! Too long since first year astronomy. That diagram thing that
shows how stars develop, you know, the one with star type on the X axis
and temperature on the Y...
--
+- David Given --------McQ-+
| Work: d...@tao-group.com | "The god of the Old Testament was actually a TRIBE
| Play: d...@cowlark.com | OF RENEGADE SPACE CANNIBALS." --- Robert McElwaine
+- http://www.cowlark.com -+
Serg
Sounds good. Are there any cool SF goodies (easy to make BH,
antigravity, warp drive), produced by spin foam approach? Or SF funs
should stick with strings for a while ?
Mark Atwood
>
> Sounds good. Are there any cool SF goodies (easy to make BH,
> antigravity, warp drive), produced by spin foam approach? Or SF funs
> should stick with strings for a while ?
Egan's new novel looks like it would qualify.
(Researchers playing with spin networks accidently create an "Ice-9"
of the vacuum, which starts spreading at 0.5c. Fast forward N thousand
years later, someone has a Bright Idea..)
Aaron Bergman
d...@pearl.tao.co.uk (David Given) wrote:
> I remember hearing somewhere that a black hole going phht in the vicinity
> of Earth will, in the last second of its life, emit enough energy to make
> most of the Earth just disappear, and blight the Sun sufficiently to knock
> it off the Main Trunk[1]. Has anyone got the energy emission formula
> handy?
It's worth noting that around 10^-5 g (or whatever the Plack mass is; I
think that's right) there's no particular reason to trust the
semiclassical formulae.
Aaron
Joe Slater
> I.e., in the old days scholarship was serious business, no time for
>funny stuff. (one reason Feynman used to cause twitches in the
>academic community)
What about the Alpher, Bethe, Gamow paper?
Keith Morrison
?
10^-5 grams is 10 micrograms. Somewhat larger than the realm where
quantum effects would be important.
--
Keith
Matthias Warkus
...and David Given <d...@pearl.tao.co.uk> wrote:
> [1] Aaargh! Too long since first year astronomy. That diagram thing that
> shows how stars develop, you know, the one with star type on the X axis
> and temperature on the Y...
Um, Hertzsprung-Russell diagram?
Did I spell that correctly?
mawa
--
Il ne se faut jamais moquer des misérables :
Car qui peut s'assurer d'être toujours heureux?
-- La Fontaine
Christopher M. Jones
Whoa, that's some seriously mind boggling stuff. What's
it like in the physics community these days? Mood wise?
To me it looks like there's a lot of really interesting
(and new) stuff to be studying right now and it seems
like there's a very profound revolution on the verge of
coming into being in the near future (someone(s) is(are)
going to have a breakthrough and a lot of those odd
questions (like the nature of the cosmological constant)
we have today will just snap into place). An exciting
time to be alive, let alone actively studying this stuff.
It's doubly exciting that some experimental discoveries
could be just a few years away! Almost gives me goose
bumps. The implications of micro-blackhole production
would be quite wide reaching, not the least of which
would be the inability (as the first paper mentions) to
study particle physics at shorter distance scales (i.e.
higher energy scales) than those where blackhole
production occurs.
--
What the dillio?
Aaron J. Bergman
>Aaron Bergman wrote:
>>
>> It's worth noting that around 10^-5 g (or whatever the Plack mass is; I
>> think that's right) there's no particular reason to trust the
>> semiclassical formulae.
>
>quantum effects would be important.
Bigger than you'd think, huh. But it's true (well, it's really something
like 2x10^-5).
Aaron
--
Aaron Bergman
<http://www.princeton.edu/~abergman/>
Matthew Austern
> Sea Wasp <sea...@wizvax.net> wrote:
> > I.e., in the old days scholarship was serious business, no time for
> >funny stuff. (one reason Feynman used to cause twitches in the
> >academic community)
>
> What about the Alpher, Bethe, Gamow paper?
Oh, that's just one of many examples of early-to-mid 20th century
physics jokes. (For those who don't know: the joke is entirely in the
author list. It's a perfectly serious paper, by Alpher and Gamow.
Hans Bethe had nothing to do with it; his name was added "in
absentia," because it was funnier that way. It's an important paper,
so people still refer to it, and it's usually referred to as the
$\alpha\beta\gamma$ paper.)
Another classic joke paper is one that Bethe really did write, and
that he actually managed to slip by the journal editors: a mock
derivation of the numerical value of absolute zero in celcius units
from first principles of quantum mechanics, written to poke fun at the
people who claimed mystical properties for the number 137. And then,
of course, you've got Murray Gell-Mann's frivolous naming, like "the
eightfold way" and "quarks". You can find lots more examples in a
wonderful anthology called _A Random Walk in Science_.
(And then, even though it's considerably later, there's the story of
how "penguin diagrams" were named.)
It probably is true that "in the old days" scholarship was serious
business, but I think those old days were pre-20th century.
Philip Armstrong
David Given <d...@pearl.tao.co.uk> wrote:
>it off the Main Trunk[1]. Has anyone got the energy emission formula
>handy?
>
>[1] Aaargh! Too long since first year astronomy. That diagram thing that
>shows how stars develop, you know, the one with star type on the X axis
>and temperature on the Y...
You're thinking of the main sequence on the Hertzprung-Russell (sp?)
diagram I believe!
Phil
--
http://www.kantaka.co.uk/ .oOo. public key: http://www.kantaka.co.uk/gpg.txt
Steinn Sigurdsson
> "Aaron Bergman" <aber...@princeton.edu> wrote:
> > So, how can we measure the number of dimensions? If we have a force that
> > obeys Gauss's law, then, in D dimensions, the force between two
> > particles scales as r^-(D-2). If the extra dimensions were curled up
> > really small, then, at large scales, the force doesn't really have
...
> > quantum gravity. So, people have started to explore what might happen.
> > Recently, Steve Giddings and Scott Thomas wrote that one might produce
> > black holes in the colliders and what the consequences of that would be.
> > The paper is available online at
> > <http://xxx.lanl.gov/abs/hep-ph/0106219>. Savas Dimopoulos and Greg
> > Landsberg have similar ideas <http://xxx.lanl.gov/abs/hep-ph/0106295>.
> > Needless to say, it would be quite cool if all this were true. I'm not
> > really sure I believe it, though. It makes some pictures that are quite
> > nice a bit more complicated. Who knows, though. Maybe we'll see when LHC
> > turns on.
> Whoa, that's some seriously mind boggling stuff. What's
> it like in the physics community these days? Mood wise?
"Interesting Times" - not clear if anything
will come of it.
For those put off by xxx/arXiv cites,
this weeks (Sep 29) New Scientist has
decent summaries of some recent speculation,
hyped up to the level New Scientist has been
reveling in recently - good fun.
Aaron Bergman
I just put those there for the curious. I hope my explanations were
accessible; atleast that what I was aiming for.
> this weeks (Sep 29) New Scientist has
> decent summaries of some recent speculation,
> hyped up to the level New Scientist has been
> reveling in recently - good fun.
Of course, if you want something really controversial, there's always
Ekpyrosis, the theory that the universe really didn't begin in a
pointlike singularity, but instead two of these branes smashed into
eachother and heated up the whole universe at once.
Aaron
Erik Max Francis
> 10^-5 grams is 10 micrograms. Somewhat larger than the realm where
> quantum effects would be important.
Not if all that mass is crammed in a single particle. The Planck mass
is in fact 2.177 x 10^-8 kg.
--
Erik Max Francis / m...@alcyone.com / http://www.alcyone.com/max/
__ San Jose, CA, US / 37 20 N 121 53 W / ICQ16063900 / &tSftDotIotE
/ \ I love mankind; it's people I can't stand.
\__/ Charles Schultz
REALpolitik / http://www.realpolitik.com/
Get your own customized newsfeed online in realtime ... for free!
Erik Max Francis
> Um, Hertzsprung-Russell diagram?
>
> Did I spell that correctly?
Yes. It's used so much in astronomy that it tends to just get called an
H-R diagram.
Erik Max Francis
> In article <0kpso9...@172.16.100.66>,
> David Given <d...@pearl.tao.co.uk> wrote:
>
> >[1] Aaargh! Too long since first year astronomy. That diagram thing
> > that
> >shows how stars develop, you know, the one with star type on the X
> > axis
> >and temperature on the Y...
>
> You're thinking of the main sequence on the Hertzprung-Russell (sp?)
> diagram I believe!
And note that an H-R diagram contains spectral type, temperature, or
color index (they're all related) on the x axis and absolute magnitude
or intrinsic luminosity (also related) on the y axis.
Aaron Bergman
"Christopher M. Jones" <christ...@keepurspamtoyerself.qwest.net>
wrote:
> Whoa, that's some seriously mind boggling stuff. What's
> it like in the physics community these days?
Well, it's a big community.
> Mood wise?
As always, depends on the person. There haven't been all that many
brilliant new ideas in the last few months, so things have slown down
significantly.
> To me it looks like there's a lot of really interesting
> (and new) stuff to be studying right now and it seems
> like there's a very profound revolution on the verge of
> coming into being in the near future (someone(s) is(are)
> going to have a breakthrough and a lot of those odd
> questions (like the nature of the cosmological constant)
> we have today will just snap into place).
We can only hope. There are a bunch of ideas, but these are really hard
problems and there's a paucity of data.
> An exciting
> time to be alive, let alone actively studying this stuff.
All this braneworld stuff is really about two years old. People had the
idea, a decent chunk of community started working on it, and people are,
unfortunately, running out of new things to say.
> It's doubly exciting that some experimental discoveries
> could be just a few years away!
It would be nice, certainly, but, to be honest, I'm not sure how many
people really believe in the TeV scale gravity thing.
Aaron
Keith Morrison
>
> Keith Morrison wrote:
>
> > 10^-5 grams is 10 micrograms. Somewhat larger than the realm where
> > quantum effects would be important.
>
> Not if all that mass is crammed in a single particle. The Planck mass
> is in fact 2.177 x 10^-8 kg.
Ah, gotcha. I hadn't run across Planck mass before. Sorry for the
stupidity.
--
Keith
Steinn Sigurdsson
> In article <rx7vgi4...@najma.astro.psu.edu>,
> Steinn Sigurdsson <ste...@najma.astro.psu.edu> wrote:
> > For those put off by xxx/arXiv cites,
> I just put those there for the curious. I hope my explanations were
> accessible; atleast that what I was aiming for.
Your explanations are very good, I just happened to
know New Scientist had a special issue this week on
the topic, and they have several longer articles expounding
on some of the issues (including the BH formation)
in their usual (slightly breathless but very entertaining) style.
> > this weeks (Sep 29) New Scientist has
> > decent summaries of some recent speculation,
> > hyped up to the level New Scientist has been
> > reveling in recently - good fun.
> Of course, if you want something really controversial, there's always
> Ekpyrosis, the theory that the universe really didn't begin in a
> pointlike singularity, but instead two of these branes smashed into
> eachother and heated up the whole universe at once.
"really controversial"? - I always took that as a slightish modification
of continuing inflation, with a specific physical mechanism and
worrying about the borders rather than the interior, but not
that fundamentally different.
The "manyfold" universe I'd consider quite controversial,
but last I looked the details don't seem to work out...
Aaron Bergman
Steinn Sigurdsson <ste...@najma.astro.psu.edu> wrote:
> Aaron Bergman <aber...@princeton.edu> writes:
>
> > Of course, if you want something really controversial, there's always
> > Ekpyrosis, the theory that the universe really didn't begin in a
> > pointlike singularity, but instead two of these branes smashed into
> > eachother and heated up the whole universe at once.
>
> "really controversial"? - I always took that as a slightish modification
> of continuing inflation, with a specific physical mechanism and
> worrying about the borders rather than the interior, but not
> that fundamentally different.
Ekpyrosis doesn't have inflation at all. That's one of the things that
makes it controversial.
Aaron
Alan McIntire
The temperature of a black hole would be (6/(M*(10^8))) degrees
Kelvin, where M=1 is the mass of the sun.
The temperature of the background universe is about 2.7 degrees K,
any black hole that formed after the original formation of the stars
and galaxies would have an effective temperature way lower than this,
and would not yet be radiating at all.- A. McIntire
Steinn Sigurdsson
> > Aaron Bergman <aber...@princeton.edu> writes:
Silly me, I had vague memories that the pre-collision initial
conditions required a de Sitter phase to establish the flatness
of the membranes, but I gather this is not the case and
flatness follows from natural vacuum initial conditions.
Funky.
I should keep up or keep shut up.
Aaron Bergman
Steinn Sigurdsson <ste...@najma.astro.psu.edu> wrote:
Well, it follows from something. That's part of the controversy. Linde
et al has published a couple of papers and Khoury et al have published a
number of responses. There are also some critiques by Lyth and a few
others.
Aaron