
Rethinking the origins of the universe - cyang08
http://unc.edu/spotlight/rethinking-the-origins-of-the-universe/
======
lutusp
Quote: "Experimental evidence may one day provide physical proof as to whether
or not black holes exist in the universe. But for now, Mersini-Houghton says
the mathematics are conclusive."

Not as conclusive as the evidence for black holes. Remember that the article's
hypothesis requires proof that black holes do not exist -- in other words,
proof of a negative. Proof of a negative is generally regarded as an
impossible evidentiary burden, and calls into doubt the hypothesis that relies
on it.

There's pretty good evidence for very large, very dense masses at the center
of most galaxies including our own. The default conclusion based on the
evidence is that they're black holes -- they have the right mass and density.

We should all remember that a mathematical theory isn't a scientific theory
until observation bears it out (produces positive evidence), and to the
exclusion of competing explanations.

------
JSPy
This doesn't really mean anything, as the work isn't peer-reviewed yet.
However, if this does become accepted it will have an extremely large impact
in Physics. The fact that this could do away with the information paradox and
add some harmony between General Relativity and Quantum Mechanics is a big
deal. Furthermore, as the title suggests, we have to rethink the origins of
our universe.

------
scott_s
I think that interested people should just read the abstract, introduction and
conclusions of the actual paper:
[http://arxiv.org/abs/arXiv:1409.1837](http://arxiv.org/abs/arXiv:1409.1837)

You will not understand the full implications of it (well, unless you are an
astrophysicist), and I didn't bother with the meat of the paper (because I am
also not an astrophysicist). But the abstract, introduction and conclusion are
rather understandable, and far less hyperbolic than the press release. And
even though I can't understand all of it, I'd much rather get a
misunderstanding from the original source material, then get a compounded
misunderstanding from a press-release.

------
scobar
The article mentioned, "Mersini-Houghton shows that by giving off this
radiation, the star also sheds mass. So much so that as it shrinks it no
longer has the density to become a black hole."

If anyone else wondered how the radiation of massless particles could result
in the reduction of mass, I've found a resource with simple explanations for a
layperson like myself. [https://www.physicsforums.com/threads/mass-lost-by-
the-sun-b...](https://www.physicsforums.com/threads/mass-lost-by-the-sun-by-
emitting-radiation.708814/)

------
ISL
Interesting; if the paper finds general acceptance, it'll be fun to watch a
new flurry of activity. The fairly recent controversial concept of "firewalls"
has reinvigorated that subfield of physics.

Whether black holes exist or not, there's something _really_ dense at the
center of our galaxy. It's a challenge to come up with a consistent non-black-
hole explanation for the observed motion of stars at the galactic center.

[http://www.galacticcenter.astro.ucla.edu/images/2011orbits_a...](http://www.galacticcenter.astro.ucla.edu/images/2011orbits_animfull.gif)

More here:
[http://www.galacticcenter.astro.ucla.edu/journey/smbh.html](http://www.galacticcenter.astro.ucla.edu/journey/smbh.html)

~~~
dennisnedry
This is why I love astrophysics (and the scientific method). When you find
something conclusive (assuming the paper is accurate), and it causes you to
re-think what you thought you knew about the universe, it suddenly becomes
larger than you ever believed possible. I hope this paper is true - since it
solves the information paradox.

------
dllthomas
_" from Star Trek to Hollywood"_

So... Hollywood? Star Trek wasn't filmed on location - Desilu and Paramount
were both located in Hollywood.

Not that this, y'know, matters - just found it amusing.

~~~
pluma
Filming Star Trek on location would have been pretty difficult, I'd imagine.

~~~
Tloewald
Well San Francisco, Cape Canaveral, and New York City figure in various
episodes and movies. (Just off the top of my head.)

------
trhway
related tidbit:

[http://en.wikipedia.org/wiki/Black_hole#Evaporation](http://en.wikipedia.org/wiki/Black_hole#Evaporation)

"A stellar black hole of one solar mass has a Hawking temperature of about 100
nanokelvins. This is far less than the 2.7 K temperature of the cosmic
microwave background radiation. Stellar-mass or larger black holes receive
more mass from the cosmic microwave background than they emit through Hawking
radiation and thus will grow instead of shrink. "

------
StefanKarpinski
This paper claims that black holes can't come into existence, which is subtly
different from claiming that they cannot exist. In particular, black holes can
exist as long as they've always existed – it's just that new ones can't come
into existence. Maybe the universe just has a fixed number of singularities.
[I am not a physicist – this just struck me as an inaccurate implication in
the article.]

~~~
wuliwong
I agree that it seems as if the article is a bit overzealous as to the
implications of this work (claiming singularities cannot exist, in particular
the one from which the big bang expanded). But, your idea that something has
"always existed" in a universe that hasn't "always existed" doesn't seem
plausible.

The author's claim that the big bang theory is now invalid because of this
calculation of energy loss of a collapsing star being too fast to result in a
black hole seems incorrect to me. The singularity from which the universe
expanded (according to the big bang) is sort of "untouchable" by physics at
the moment. I would guess there are some of the string/brane theory models out
there that postulate what caused the big bang but currently it is my
understanding that whatever information was around about the cause of that
singularity is not accessible to us. Again, who knows what we will discover in
the future but as of now, making any bold assertion about the lack of
existence of that initial singularity seems presumptuous.

~~~
kuhhk
You're experiencing cognitive bias.

If it is presumptuous to present calculations that may invalidate a _theory_
based on assumptions, then it is also presumptuous to disregard such
calculations and state that the _theory_ itself is automagically correct, just
because the assumptions are untouchable.

A bold assertion indeed.

------
danbruc
Well, there is are a lot of observational evidence for black holes - the by
far most likely scenario is that the model they analyzed does not describe the
physics of black holes in our universe.

~~~
tericho
This is the first question I thought of. I'm not a physicist so I dare say I
can't interpret the paper but I'm curious how she explains the _seemingly_
observed orbits of stars around the black hole in the middle of our galaxy and
others[1][2].

[1][http://astro.uchicago.edu/cosmus/projects/UCLA_GCG/](http://astro.uchicago.edu/cosmus/projects/UCLA_GCG/)
[2][http://en.wikipedia.org/wiki/Accretion_disc](http://en.wikipedia.org/wiki/Accretion_disc)

------
faizshah
I'm not at all acquainted with astrophysics but I remember seeing an article
state that there was a different physicist who proved this same thing:

[https://news.ycombinator.com/item?id=7191324](https://news.ycombinator.com/item?id=7191324)

A quick google shows his response to this:

[https://twitter.com/abhasmitra/status/514804101024997376](https://twitter.com/abhasmitra/status/514804101024997376)

His response:

"Hawking radiation is unproven. And particle physicists are not aware that
even without any Quantum Mechanics, classical gravitation dictates that all
gravitational collapse must be accompanied by radiation. :

[http://link.aps.org/doi/10.1103/PhysRevD.74.024010](http://link.aps.org/doi/10.1103/PhysRevD.74.024010)

([http://arxiv.org/pdf/gr-qc/0605066v3.pdf](http://arxiv.org/pdf/gr-
qc/0605066v3.pdf))

And then grav collapse should naturally lead to radiation supported ECO:
[http://www.sciencedirect.com/science/article/pii/S1384107606...](http://www.sciencedirect.com/science/article/pii/S1384107606000923)

[http://mnras.oxfordjournals.org/content/369/1/492](http://mnras.oxfordjournals.org/content/369/1/492)

[http://mnrasl.oxfordjournals.org/content/404/1/L50](http://mnrasl.oxfordjournals.org/content/404/1/L50)

And as far as non -formation of ``Event Horizon'' is concerned, in contrast to
the conjectures of the present yet unpublished paper I gave EXACT proof:

[http://www.ias.ac.in/pramana/v73/p615/fulltext.pdf](http://www.ias.ac.in/pramana/v73/p615/fulltext.pdf)

But phys.org never highlighted my research which is infinitely more accurate
than the present paper whose authors are not even aware that Question of
Hawking Radiation Would Arise Only If There Would Already Be a Black Hole With
an Event Horizon. Therefore This paper is not self-consistent. But that does
not matter:

The lead author of this paper has CAMBRIDGE AFFILIATION.

So phys.org is glad to highlight an inconsistent and yet unpublished paper by
ignoring my series of my exact and original papers on the same topic."

I don't have any background in astrophysics, can anyone comment on Dr. Mitra's
response and the relation of his work to the above research?

The best discussion I can find on Dr. Mitra's work is on quora:
[https://www.quora.com/Is-it-true-that-Abhas-Mitra-
resolved-t...](https://www.quora.com/Is-it-true-that-Abhas-Mitra-resolved-the-
Black-Hole-paradox-13-years-before-Stephen-Hawking)

~~~
trhway
>But phys.org never highlighted my research which is infinitely more accurate
than [...]

>The lead author of this paper has CAMBRIDGE AFFILIATION.

>So phys.org is glad to highlight an inconsistent and yet unpublished paper by
ignoring my series of my exact and original papers on the same topic."

welcome to modern science. It is a professional guild like a guild of
shoemakers of Middle Age Europe cities with about the same rules. Or like
another my friend (former second-rate professor from a first rate university
:) put it - it is a mafia, at every level. Researchers of the highest tier
universities publish in the highest tier journals, researchers of the next
tier - in the next tier journals, ... A good physicist should be able to
understand the laws of Nature behind such formation :)

------
davesque
From the article:

"Laura Mersini-Houghton has mathematically proven that quantum effects are
strong enough to stop the formation of black holes..."

If I'm not mistaken, Mersini-Houghton's work has just hit the scene. It still
has to be vetted by the larger community before we could say that anything's
been "proven."

~~~
lutusp
Not to mention what I'm about to -- that scientific theories are never proven,
only disproven. You can always tell when a journalist is speaking about a
topic for which a scientist might be a better source.

As to "mathematically proven", it's an unfortunate juxtaposition of math
(where things really can be conclusively proven) and physics (where they
cannot be).

~~~
davesque
Right. I was going to mention that as well, but didn't want to be too knit
picky :).

------
z3t4
What many people seem to overlook is that gravity is linked to time (space
time)!

So instead of the "black hole" being massive, it could be that time is running
fast!

~~~
seiji
Well, "linked" is vague. They aren't linked—they are the same thing! Gravity
is an effect mass has on the upholstery of the universe. Time runs slower for
us here inside the gravity well of Earth than it does for astronauts in zero
gravity.

You can't create time distortions without gravity distortions, and you can't
create gravity distortions without instantiating mass, so... big massive black
holes have to be running slow; if they exist at all and aren't just cosmic
bees sitting at the 2D boundary of the universe and projecting nothingness
into our inflated space.

~~~
lutusp
> They aren't linked—they are the same thing!

If you're speaking of time and space, no, they're different -- they're
certainly all part of one spacetime, but they're distinct. This distinct:

t' = t √(1-v^2/c^2)

t = time

v = velocity

c = speed of light

t' = time at velocity v relative to velocity 0

Put into words, this special relativity relationship shows that an increase in
velocity (movement in space) causes a reduction in time's rate of passing
(movement in time). The general relativity version has more terms, and shows a
relationship between mass and both space and time.

So space, time and mass aren't the same thing, but they're part of an
interrelated system, one easily described mathematically.

> Time runs slower for us here inside the gravity well of Earth than it does
> for astronauts in zero gravity.

Yes, true, but astronauts in orbit aren't in zero gravity, they're in free-
fall. The gravitational force at typical orbital heights is nearly as strong
as it is at the surface.

------
tfgg
"In 1974, Stephen Hawking used quantum mechanics to show that black holes emit
radiation. Since then, scientists have detected fingerprints in the cosmos
that are consistent with this radiation, identifying an ever-increasing list
of the universe’s black holes."

Er, what? I don't think this is true, or Hawking would have his Nobel prize by
now. Maybe consistent in the sense that the predictions are that Hawking
radiation is undetectably low for stellar mass black holes. Also, analogue
systems don't count.

~~~
vorg
> "Stephen Hawking used quantum mechanics to show that black holes emit
> radiation." I don't think this is true, or Hawking would have his Nobel
> prize by now

Hawking not getting a Nobel by now doesn't mean much. Einstein never got one
for relativity (either Special or General), and when he did get his Nobel he
was told not to mention "relativity" in his speech.

~~~
jorgis
Einstein guy his for his work with Brownian Motion. Nobel prizes aren't
typically given for science that lacks a body of supporting evidence, which
was the case at the time for Relativity.

------
Fool40
Just downloaded the PDF, I am not a physicien nor a mathematicien.

but from what I read in the article the EQ 13, is the weakness of their
argumentation.

AA

~~~
Fool40
Their boundery limit pose a problem, and then the entire solution in the
extending (prior explosion) the radius is greater the rs, and so all the
fellowing integral are wrong. but I will wait for Hawking opinion :)

------
waynecochran
Interesting to note that LIGO
[http://www.ligo.caltech.edu](http://www.ligo.caltech.edu) never detected any
gravity waves (supposedly created by colliding black holes). This is the NSF's
most ambitious project and they have spent (still are spending) a butt load of
money on it.

------
trhway
Ok. To start she addresses only "Gravitationally Collapsing Star"s.
Interesting result, may be many star lifecycles don't end in a black hole. The
"before-black-hole" state she describes still would involve significant time
dilation and thus what we see as Hawking radiation from black hole may just be
Hawking radiation from "before-black-hole" star. Looks the same :)

The result doesn't say that black hole is impossible. It says that a star's
collapse loses mass faster than acceptable for the collapse to end in black
hole.

Some misconceptions in the web-post:

>They are the ultimate unknown – the blackest and most dense objects in the
universe that do not even let light escape.

a black hole isn't necessary most dense. After all a black hole with a mass of
visible Universe would be only 125 times denser than current average density
of the visible Universe (i.e. 45B light years radius of visible Universe have
10B light years Schwarzschild radius)

> So the story went, an invisible membrane known as the event horizon
> surrounds the singularity and crossing this horizon means that you could
> never cross back. It’s the point where a black hole’s gravitational pull is
> so strong that nothing can escape it.

"membrane" is very bad illustration. It is constantly changing solution to the
gravitational equations. One moment it is here, another moment - it has moved
because gravitation of black hole changes and a lot of
oscillations/perturbations happen. One moment you're inside, another -
outside.

"gravitational pull is so strong that nothing can escape it" \- that's bad
wording too. It is actually "gravitational well is so deep that nothing can
escape it". Feel the difference :) A huge black hole may have pretty weak
gravitation at its horizon.

Thus no-escape is valid only in the sense that escaping object just would
never reach "a point at infinity" from the black hole and the light would get
red-shifted into full oblivion.

~~~
lutusp
> A huge black hole may have pretty weak gravitation at its horizon.

Not really. The amount of spacetime curvature at the event horizon is fixed in
the theory -- it's always the same. It's how the event horizon is defined.
Near the event horizon, light orbits endlessly (in principle), and (again in
principle) if you were located at an event horizon and there was sufficient
illumination, anywhere you turned you would see the back of your own head.

> Thus no-escape is valid only in the sense that escaping object just would
> never reach "a point at infinity" from the black hole and the light would
> get red-shifted into full oblivion.

From a more distant frame of reference, yes, but not at the event horizon
itself.

~~~
dragonwriter
> The amount of spacetime curvature at the event horizon is fixed in the
> theory -- it's always the same.

No, its greater the smaller the horizon is (so, equivalently, less the bigger
the horizon is).

> Near the event horizon, light orbits endlessly (in principle)

Sure, at the event horizon, light orbits endlessly. But the amount of
curvature needed to do that is less the further across the horizon is.

~~~
lutusp
>> The amount of spacetime curvature at the event horizon is fixed in the
theory -- it's always the same.

> No, its greater the smaller the horizon is (so, equivalently, less the
> bigger the horizon is).

We're using different meanings of "curvature". For all black holes regardless
of their properties, the event horizon has the same spacetime curvature --
that required to produce orbiting photons that cannot escape. Outside the
event horizon, photons can escape. Inside, they cannot (and those photons
don't orbit either, but cross the horizon). All the same.

> But the amount of curvature needed to do that is less the further across the
> horizon is.

No, it's the same. Same curvature, different large-scale geometry. For a
sufficiently small zone near the event horizon, the conditions are identical.

Again, this is about the meaning of "curvature". The circumference of the
horizon is greater for a large mass than a small one, but the spacetime
curvature at the horizon is the same -- it's the specific value that causes
photons to orbit perpetually, and interestingly from a local perspective, the
entire horizon surface appears as a plane of infinite extent, sort of like two
facing mirrors but with more dimensions.

From the perspective of a hypothetical observer at the horizon, he wouldn't be
able to judge the size of the black hole using local observations -- there
would be a plane of infinite extent for any black hole regardless of size.

------
xefer
If I read the abstract and introduction correctly, it doesn't say that black
holes per se don't exist, only that they can't form as the result of a
collapsing star or supernova. The linked-to article seems to be jumping to
conclusions (e.g., rethinking the origin of the universe; impossibility of
black holes at all, etc.) that the paper isn't even making.

------
houseofshards
Isn't there a lot of observational evidence for black holes ?

------
paramendra
If black holes don't exist, what are those massive things at the centers of
galaxies?

~~~
chris_mahan
They're complexity anomalies. Things can't resolve themselves out and so stay
in.

------
tericho
Ethan Siegel just posted a detailed response to this.

[https://medium.com/starts-with-a-bang/yes-virginia-black-
hol...](https://medium.com/starts-with-a-bang/yes-virginia-black-holes-exist-
df0a131d7b95)

~~~
scott_s
I don't think that is a response to this work. That is dated February 1. He
links to this paper's author, Laura Mersini-Houghton, but he links to a paper
and blog post of hers from January. Reading that blog post
([http://backreaction.blogspot.com/2014/01/if-it-quacks-
like-b...](http://backreaction.blogspot.com/2014/01/if-it-quacks-like-black-
hole.html)), what she says seems to be in contradiction with the more recent
paper she wrote
([http://arxiv.org/abs/arXiv:1409.1837](http://arxiv.org/abs/arXiv:1409.1837)).

In her blog post from January, she says:

 _" What Hawking is saying is essentially that he believes that a matter
collapse only leads to a temporary apparent horizon but not to an eternal
event horizon. That is an opinion which is shared by many of his colleagues
(including me) and there is nothing new about this idea whatsoever."_

But in her more recent paper, she says:

 _" More specifically, we find that collapsing stars slow down their collapse
right outside their horizon, while substantially reducing their mass through
Hawking radiation. ... The star never crosses its horizon, so neither
unitarity nor causality are violated, thereby solving the longstanding
information loss paradox. This investigation shows that universally collapsing
stars bounce into an expand- ing phase and probably blow up, instead of
collapsing to a black hole."_

I am not a physicist, but when I read those two statements, they are in
contradiction. The first statement says to me: it may not be an absolute
horizon, but it is _a_ horizon. The second statement says to me: actually, we
never reach any horizon. So I think that the more recent statement means that
she has changed her conclusions based on her recent work.

~~~
aruggirello
I'm confused here. The mere existence of an event horizon - albeit a temporary
one - should make a black hole! So "More specifically, we find that collapsing
stars slow down their collapse right outside their horizon," by implying that
a horizon DOES exist, simply doesn't cut it. Am I missing something?

~~~
scott_s
I believe that's using the _concept_ of a horizon. For an object of a
particular mass, we can use our theory to tell us where the event horizon
would be, _if it collapses past that point_. My understanding of this recent
paper is that they are saying: it won't collapse past that point.

------
oAlbe
> _a fundamental law of quantum theory states that no information from the
> universe can ever disappear_

What is the name of this law?

~~~
ed
[http://en.wikipedia.org/wiki/Unitarity_(physics)](http://en.wikipedia.org/wiki/Unitarity_\(physics\))

[http://en.wikipedia.org/wiki/Black_hole_information_paradox](http://en.wikipedia.org/wiki/Black_hole_information_paradox)

------
AnimalMuppet
If I understand correctly, black holes do not play a large role in our model
of the origins of the universe. So this doesn't (directly) lead to "rethinking
the origins of the universe". Does this work call the big bang into question
(or even our current models of the big bang)? Or is it just details like
galaxy formation that it makes us rethink?

Another question: _Something_ very massive and very small is at the center of
our galaxy. At least, we sure think so. Does this make us question that? Or
does this just make us question whether that massive thing is in fact a black
hole?

~~~
tjradcliffe
Your first point is correct: the relationship between black holes and the
initial state of the universe is not clear. Whether or not there was a
primordial singularity or something else is an open question.

With regard to the question "If not black holes, then what?", this is a
problem. There is a strict upper limit on neutron stars of about 1.4 solar
masses. Beyond this, gravity is stronger than the repulsive core of the strong
nuclear force, and the star should collapse. If the process described in this
paper is what actually occurs, the star will shed mass due to Hawking
radiation while collapsing. The end-state of that process must be either a
neutron star (which can't have more than 1.4 solar masses) or something else.
There doesn't seem to be any "something else" in the offing, which makes that
million-solar-mass thing in the centre of our galaxy deeply mysterious.

A new theory that makes an old "settled" phenomenon mysterious is not all that
uncommon in the sciences, so it's reasonable to take a wait-and-see attitude
toward this idea, but I'm not enormously hopeful that it'll pan out very well
in the long run.

~~~
squozzer
So it seems a cycle of collapse and Hawking radiation will occur until the
star no longer has enough mass to collapse.

------
linguafranca
My trust in metaphysical and other such sciences dropped significantly on the
day I realized that most modern conclusions are just theories and half of them
have already been proven wrong.

~~~
calinet6
That is science at its best. What, indeed, is the alternative to admitting we
were wrong when confronted with new and more accurate information? There is no
"trust" in science, there is only truth, and you must always leave room for
doubt.

Astrophysics appears volatile simply because there is so much we do not know,
but that is also what makes it fascinating, and of critical importance.

------
chc
Given how important this would be, it seems a bit odd that she just threw it
on ArXiv rather than having it peer-reviewed. Also, the press release's
explanation of what Hawking radiation is sounds strange to me, though I'm not
an astrophysicist. It all makes me very hesitant to put any stock in this
right now (well, at least it in meaning what's suggested here).

~~~
Stwerp
I understood that it was common to post the paper to arxiv when it was in the
process of being peer reviewed by a journal. The problem is the extended lag
time between submission and final publication with most journals which pre-
print archives like arxiv try to solve. Do people really just "submit to
arxiv" and then that it? I didn't know that, but its not common in my field to
use arxiv so I have not kept up with all practices.

~~~
tjradcliffe
There have been cases where arxiv has been used as a venue of final
publication, but the general intent is that stuff submitted there will
eventually find a home in the peer-reviewed literature. There are sometimes
exchanges of arguments there that never make it to prime-time, but that's not
the dominant use-case.

The reality is, though, that people working in a given field are much more
likely to use the arxiv version as the basis for further work, simply because
it is available so much earlier. It is not uncommon to reach the point of
publication and then run around to try and find out where all the arxiv
submissions you used were published, which can sometimes be challenging.

------
sramsay
I'm not a physicist. I imagine that if I were, this would be exciting news
(that is, an exciting possibility).

I _am_ a literary critic, though, and I have to say that it's bittersweet news
at best. Black holes are so much a part of the space-age imagination. The
article mentions Hollywood, but black holes are woven deeply into our everyday
metaphors and have been for decades. They have stood among the most wondrous
things in the universe -- an awe-inspiring thing.

It reminds me a bit of when the press reported that the Catholic Church had
"gotten rid of Limbo" (the actual case was a bit more complex, and involved
some fairly weighty theology).

Then again, we all still talk of things "being in Limbo." Perhaps that next
project will still be a black hole, even if it turns out that there's no such
thing.

~~~
dhimes
I imagine that the metaphor "black hole" will be here for a while. After all,
we still use the term "big bang" for the 'first moment' of the creation of the
universe, even though the "Big Bang Theory" isn't generally believed any
longer.

~~~
lutusp
> even though the "Big Bang Theory" isn't generally believed any longer.

Really? Given that science doesn't turn on belief but evidence, still, the Big
Bang remains the best explanation for existing evidence. It's the prevailing
cosmological theory of the universe' beginnings. Like all scientific theories,
it's subject to replacement as new evidence appears and as new theories are
crafted, but it's a good match at the moment.

~~~
acjohnson55
I think it's a bit naive to say that science doesn't turn on belief. Scientist
aren't robots, mechanically and dispassionately ingesting evidence and
spitting out theory. They're humans with imaginations, beliefs, agendas, and
egos, guided (hopefully) by a methodology that leads to discovery. I think
belief is what drives science, and it's not all that bad of a thing.

~~~
lutusp
> I think it's a bit naive to say that science doesn't turn on belief.

That depends entirely on what we mean when we say "science". If by "science"
we mean as defined and as practiced when it's done right, then no, belief
plays no part -- it can't. If it did, it wouldn't be science.

> Scientist aren't robots, mechanically and dispassionately ingesting evidence
> and spitting out theory.

Scientists aren't robots, but they are also not hothouse orchids.

> They're humans with imaginations, beliefs, agendas, and egos, guided
> (hopefully) by a methodology that leads to discovery.

You have left the topic of science. The reason science exists is precisely
because people are the way you describe them. Science is meant to be a
counterpoint to natural human instincts, beliefs, passions, and other logical
failings.

> I think belief is what drives science, and it's not all that bad of a thing.

You're now confusing science with religion. In religion, you let sincere
feelings guide you to a conclusion. In science, you let _logic_ guide you to a
conclusion.

In religion, something is true until evidence proves it false. In science,
something is _false until evidence proves it true_ \-- exactly the opposite.

Much of scientific discipline is meant to guard against what we believe is
true or want to be true. Experimental and control groups, the classic double-
blinding precautions in human studies -- all are meant to minimize the
corrosive, undermining influence of our beliefs.

The perfect religious follower is guided by belief, hoping only that his work
reflects his passion. The perfect scientist doesn't care what conclusion his
work comes to, hoping only that it reflects reality to the best of his
ability.

Belief and science are in absolute opposition.

~~~
cruisername
> [that it's naive to say that science doesn't turn on belief] depends
> entirely on what we mean when we say "science".

Or it depends on what we mean when we say believe. The weight lying on
"science" does form a conceptual framework that completely ignores the notion
of something beyond our reach, although it inarguably is the driving force
behind science.

> In religion, something is true until evidence proves it false. In science,
> something is false until evidence proves it true -- exactly the opposite.

alright, but the word of god himself isn't evidence enough? j/k :)

> In religion, something is true until evidence proves it false. In science,
> something is false until evidence proves it true -- exactly the opposite.

Why do those have to opposite, can't they be reconciled into one, using some
form of ternary logic? Edit: I mean, some things in life are unknown until
proven true or false and then theres all kinds of methods to counter the fact.

~~~
lutusp
> The weight lying on "science" does form a conceptual framework that
> completely ignores the notion of something beyond our reach, although it
> inarguably is the driving force behind science.

Yes, but an idea doesn't become a matter of interest to science until it comes
within our reach, in the sense of being observable in a way that forces
different, similarly equipped observers to the same conclusion (the scientific
meaning of "objective").

> Why do those have to opposite, can't they be reconciled into one, using some
> form of ternary logic?

Yes, an interesting question, but not really about science. Science concerns
itself only with things that can be reduced to empirical observation, not
belief.

> I mean, some things in life are unknown until proven true or false ...

That's true, but the basic scientific precept is the null hypothesis, the idea
that things without evidence are assumed to be false. This is a great time-
saver compared to granting credence to ideas without evidence, or assuming
that something might be true until proven false (the unscientific outlook).

~~~
cruisername
I agree with your co-commentator, everything is subjective and we just take
some things for granted so much that we take them as truth.

Seems i was wrong calling it inarguable, in fact i like to argue back and
forth a lot.

> observable in a way that forces different, similarly equipped observers to
> the same conclusion (the scientific meaning of "objective").

no, that's still subjectivity, you just shifted the goal post. That kind of
subjectivity might be your threshold for accepting some cognition as close
enough to your supposition of objectivity, but it still requires trust on an
individual level.

> an interesting question, but not really about science. Science concerns
> itself only with things that can be reduced to empirical observation, not
> belief.

Specifically by including subjectivity through empiricism, you in fact beget
belief. I.e. measurements have an inherit uncertainty and you do what you can
to reduce it.

> but the basic scientific precept is the null hypothesis, the idea that
> things without evidence are assumed to be false

You seem to fall for the fallacy of negated implication. My best guess is, the
Null Hypothesis really states that evidence implies reality.

Or as my teacher put it, just because it didn't rain, the street doesn't have
to be dry. It's hard to explain and I'm tired, sorry. I often fall for it,
too.

~~~
lutusp
> ... no, that's still subjectivity, you just shifted the goal post. That kind
> of subjectivity might be your threshold for accepting some cognition as
> close enough to your supposition of objectivity, but it still requires trust
> on an individual level.

You're making the post-modern argument. Are you aware of this? Everything is
subjective, there are no objective shared truths, it's all a matter of
opinion. But you haven't thought this viewpoint through to its logical
conclusion, which is that, if it's true, then it applies first to the argument
itself, fatally undermining it.

~~~
cruisername
I am aware of that, but I didn't think it through far enough to conclude that
it's really undermined. I dunno, say, It only makes predictions about
subjects, no the bigger picture, where a god-device would come in. It doesn't
really explain away your stand point either. Good talk :)

------
guscost
Another member of the peanut gallery here. I've not been bold enough to make
any claim in writing (it would probably be full of misconceptions), but the
black hole hypothesis always seemed a bit half-baked, and I've definitely said
words to that effect in conversation.

In the hypothesis Einstein's field equations obviously break down, and instead
of acknowledging that any explanation will be enormously difficult to test we
seem to have bought into this completely untested idea that matter can
continue bending space-time around into a singularity and all that. Can
someone with a better understanding point out what logic is (probably) missing
here?

The other thing that sets off my hand-wave-o-meter is the pretending that we
are somehow already observing these things ("new telescope detects hints of
black holes") or have concluded that they exist without any positive evidence.
Instead of "the mass at the center of the galaxy which is so large that we
currently have no good way of modeling it without a black hole" we hear "the
supermassive black hole at the center of the galaxy" and so on.

~~~
scott_s
My understanding of what Laura Mersini-Houghton's paper is claiming is that
stars cannot collapse into black holes, but they can get damned close. So
those things that we have observed are not "black holes", but things that are
damned close. In the paper, she and her co-author write, "Both effects
(slowdown and mass-loss) balance such that the evaporating star remains very
slightly outside its event horizon."

Even if this paper is correct, I don't think it's warranted to be so smug
about people thinking they found black holes. We had a theory, and we had
positive evidence for that theory. That's reasonable. If this paper is
correct, then it turns out those things are not actually "black holes", but
objects "very slightly outside" of being black holes. That's not too bad.

Disclaimer: I am not a physicist.

~~~
guscost
What is an example of this positive evidence?

Also is it at all plausible that the center of the galaxy is evaporating
slightly outside its event horizon in this way?

Anyway I'm not sure that the two of us are going to answer any of these
questions without some help.

~~~
lutusp
> What is an example of this positive evidence?

Are you asking what observational evidence exists for black holes? There are
very massive, very dense objects at the center of most galaxies, objects that
by their mass and density fall well inside the theoretical limits for black
holes. At the center of our galaxy, there is a very massive, compact object,
around which many stars are orbiting, in orbits that reveal the object's mass
and approximate size:

[http://astro.uchicago.edu/cosmus/projects/UCLA_GCG/](http://astro.uchicago.edu/cosmus/projects/UCLA_GCG/)

This is pretty good evidence -- if the object weren't within the mass/density
realm that allows for black holes, the orbiting stars couldn't approach it as
closely as they do without colliding.

Again, this doesn't prove anything, it only supports the idea that black holes
are possible, and that our observations agree with that idea.

~~~
guscost
I don't disagree with any of that, but the evidence in question still depends
on several big assumptions.

~~~
lutusp
It's the other way around. The evidence doesn't depend on the assumptions, the
assumptions depend on the evidence.

The observations are very good and offer little latitude for interpretation --
there is a very massive, very dense object at the focus of multiple stellar
orbits near the center of our galaxy, and both the mass and the density of the
object are easily and unambiguously derived from the orbits.

It's the same with other galaxies -- a massive, dense central object dominates
the orbital dynamics of the galaxy near its center. We're obviously not free
to say that means black holes exist, it's just another piece of evidence. But
it's a way to exclude certain alternatives.

~~~
guscost
Maybe it could be worded better. In order to say that gathering this evidence
is the same as directly observing a black hole, we have to make several big
assumptions.

------
phkahler
Now that all the physicists are reading, I have a question: Are the
trajectories of light beams following the curvature of space-time reversible?
In other words, if I reflect a light beam back on itself, does it return to
its source?

Because if that's true (and my feeble understanding is that it is true), then
light can't enter a black hole or the reverse path would allow light to
escape. What am I missing here?

~~~
antognini
If the spacetime is static, then yes, the trajectory of a light beam (or
anything else) is reversible. The question you pose is an excellent one and is
one of the reasons that many physicists believed that black holes could not
exist after Karl Schwarzschild discovered the Schwarzschild metric that
describes spacetime around a spherically symmetric black hole.

So what happens if you direct a beam of light radially into a black hole? A
distant observer will calculate that as the light beam descends into the black
hole it will be (according to a distant observer) progressively blueshifted
until it reaches the event horizon, at which point it will have blueshifted to
infinite energy. In fact, according to the calculations of a distant observer,
the light beam will never cross the event horizon, so the statement that the
light beam is reversible remains true. The reason that the light beam
(according to the distant observer) doesn't cross the horizon is that if you
look at the metric, it states that ds^2 = (1 - R_Schw / r) c^2 dt^2 - 1 / (1 -
R_Schw / r) dr^2, where R_Schw is the radius of the event horizon. Notice that
at the event horizon r = R_Schw and the dr^2 term diverges. The distant
observer therefore concludes that there is a singularity at the event horizon.
This analysis lead physicists to initially conclude that black holes were
unphysical.

A more careful analysis reveals that this isn't the case, however. We have
been using this metric which describes the shape of spacetime according to a
distant observer. But what we're really concerned with is not what a distant
observer calculates, but how a _local_ observer perceives spacetime. If we now
switch to a coordinate system in which we are free falling into the black hole
along with the beam of light, we find that nothing remarkable happens when we
cross the event horizon. The light is blueshifted relative to its initial
energy, but it doesn't have an infinite amount of energy. Thus there is no
true singularity at the event horizon. This singularity that the distant
observer found must therefore have been an artifact of the particular
coordinate system that the distant observer was using. The free falling
observer can then hold up a mirror and send off a light beam and have it
return back to him even after they have crossed the event horizon.

~~~
lisper
You have this backwards. To a distant observer, light going into a black hole
is red-shifted, not blue-shifted. If this were not the case, sending even a
single photon into a black hole would produce infinite energy.

~~~
antognini
No, any photons that are emitted from matter close to the event horizon and
travel _toward_ the distant observer will be redshifted. Photons falling into
the potential well of the black hole will be blueshifted. Of course, the
distant observer is not able to directly detect photons falling into the black
hole because he is far away from it. All he can do is calculate what he would
expect the energy of the photons to be. This calculation gives an infinite
energy as the photon approaches the event horizon, but it's not a "real"
energy, so the black hole doesn't gain an infinite amount of energy.

An analogous effect occurs for an observer stationed at rest, hovering above
the event horizon. Such an observer will observe the photons from afar to be
blueshifed in agreement with the distant observer. Moreover, as this
stationary observer gets closer and closer to the event horizon, the photons
will be blueshifted to infinitely large energies.

~~~
lisper
Ah. OK, I misunderstood what you were saying. This is right.

