Olbers' Paradox

Whatever you're on, can I have a pint of it, please?

No, because it's seriously far too strong for you.

Human vision relies on reflected light; if there is no reflection we can't see it. We can't see air, but it's still there. Color is perceived by humans via various wavelengths of light being reflected off a surface, space has no reflection and therefore no color.

If space were static, infinite in size and age, any direction you looked would be the surface of a star. That's Olber's paradox.

But the universe has a finite age, and since the speed of light is finite, there is an observable horizon beyond which we cannot see. Another reason is that space is expanding so that the light given off in the farthest reaches of the observable universe is redshifted to the microwave wavelengths (about 3 deg K).

https://en.wikipedia.org/wiki/Observable_universe

True but even with the near steady state universe scenario of looking just within one galaxy, Olber's paradox is not a real paradox. The Hertzsprung–Russell diagram presents the measured luminosity of the stars found in the Milky Way.

The range of this luminosity is some eleven to twelve orders in magnitude. Since light attenuates with the square of the distance it travels it takes just 10^6 light years of distance for the brightest luminosity star to appear as bright as the dimmest star that is only 1 light year away. Our Milky Way galaxy has a nominal diameter of 10^6 light years. This is why even when we look directly along the galactic ecliptic at the densest aggregation of stars in the Milky Way, Olbers' Paradox is shown to be a false paradox.

There aren’t enough stars in the Milky Way for Olber's paradox to work, but when he stated it the concept of galaxies didn’t exist, and the basis of the paradox was space being static, and infinite in size and age (as Rixter said in #5).

As you say it doesn’t work for the Milky Way or any individual galaxy, also for reason below.

I understand a typical galaxy is 10⁵ ly dia, 10⁴ ly thick (10⁶ ly is average distance between galaxies).

Looking at it edge-on (minimum area) that = 10⁹ ly² ~ 10⁹ x 10³² = 10⁴¹m² (1 ly ~ 10¹⁶m).

Number of stars per galaxy ~ 10¹¹. Taking the Sun as a typical star, radius ~ 7*10⁸ m, area = 10¹⁸ m² (to nearest order of magnitude). Total star area 10²⁹ m².

So fraction of area occupied by a star = 10²⁹/10⁴¹ = 10^-12 – negligible.

TV Cosmologists Repent !

Wow ! Rixter, you constantly demonstrate an amazing level of being well informed.
I assimilate your distinction of red shift due to universe expansion as being different
from redshift due to classical Doppler. I also recognize that there is layer after layer of
evidence from somewhat different mechanisms leading to increasing velocities the farther
out one looks. With massive effort, one might be able to piecewise overlap these mechanisms
across their ranges to arrive at a strong argument for the currently fashionable model of
the behavior of the universe as expanding and accelerating in that expansion.

Unfortunately,
I find myself still yearning for a credible measure of velocity from something other than
phenomena which ostensibly measure velocity via some side effect of velocity which might
have powerful alternative modulators in favor of dividing delta distance by delta time.
Delta time is therefore still a serious issue given lifetimes being so short and human
history being not seriously longer. Given the history of human estimations of the extent
of human history(eg., "The Earth is about 6 thousand years old" widely believed only a few
hundred years ago) we should clearly retain a healthy skepticism of popular wisdom. Now,
I grant that our wisdom(or at least our ego) has expanded even faster than our estimation of
the size of the universe(sarcasm, but I do see that we probably are a bit more careful
and even sometimes more scientific than emotive in our print pronouncements than we once
were.) We still do seem to use the term "know" a bit more than we deserve to.

So, for all of that ranting, what do I really expect to gain, you may be asking. I hope
that, besides proving myself not fully informed, someone might provide a credible thought
experiment which without years of tedious study, I might adopt as my own to be spouted to
those who have issues with universe expansion and in particular universe expansion at rates
casually described as faster than the speed of light. On the black hole front, I would love
it if someone could realize that random masses traveling at relativistic speeds in basically
random directions could never reach a central singularity. I loved it when Max Tegmark,
unlike all the other talking heads, said that the singularity is proof that we do not know
what is really happening in black holes and did not revert to "this is where the laws of
physics break down." Basically, I want to believe our experts and red flags go off in my
head whenever I hear anything which smells of what we used to call "hand waving" in my
science classes of decades ago. I recall a cartoon which showed several large chalkboards
crammed with calculations, a tiny line that says "and then a miracle occurs", and then some
grand conclusion. That is, I want scientists to act their part instead of the part of some
religious authority demanding that the unwashed rabble accept concepts on faith.

I recognize that many scientists of high visibility will off-the-record quote, "the truth,
you can't handle the truth" and for many who find thinking unpleasant they are right.
Generally, I want to encourage them to realize that there are some still out here who can
handle statements which are longer than twitter will allow. In particular, they need to be
candid about their internal recognition of the weakness of any statement promoted as
"confirmed truth" and be willing to identify their perspective of those weaknesses.
I want TV scientists to ignore the adamantly ignorant and address those of us who can and
will think. After all, these are shows identified as genre scientific and follow a
distinguished history including "Mr. Wizard", Feynmann(various shows), and "Cosmos" which
were not perfect in my estimation but "not bad, not too bad at all" at being candid and
accurate.

Rixter, have you ever considered doing some TV ?
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thewildotter

Regretfully, if there is a Nobel prize in the offing, you might have to share it with Homer Simpson. In the Stephen Hawking meets Homer Simpson episode, Hawking asks Homer, "Please tell me more about your theory of a donut shaped universe."

Silliness aside, I too have never found the red shift argument for an expanding universe to be entirely convincing. As you suggest, over such staggering distances and times, how can astrophysicists be so certain that other things are not at play to cause the observable red shift? ("There are more things in heaven and earth, Horatio, than are dreamt of in your philosophy." - Hamlet ) Thankyou for articulating your scepticism.

Inescapable

Sometimes Lisa, Marge, Maggie, and even Homer are way smarter than one expects in a cartoon show. Just to keep the record straight, I was promoting a donut shaped black hole as opposed to a donut shaped universe. Someone told me that Hawking at one time suggested that black holes were toruses but that he had since recanted. I confess that I have not tried to research that rumor. I was hoping that the idea would regain authoritative support before I looked at it again. I really do not enjoy reading or hearing some respected scientific icon spouting something to which my brain instantly flashes up a big flashing sign that says, RIDICULOUS. That was the image I got when they said that he had recanted. The promised picture of the MilkyWay black hole revived hope that the great nebulous THEY would revisit what, at least for now, seems inescapable(pun) to me. Do we have pictures yet ?

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thewildotter

When I was young I too thought the expansion of the universe, by way of the big bang theory, was unsupported or at the very least had fragile support. What you seem to not be aware of is the pivotal discovery that put the big bang theory as the preeminent cosmological theory.

The theorists looking into the nuances of the proposed big bang theory realized that the theory implied that microwave radiation had to be left everywhere. This residual energy intuitively seemed to be wrong to them so they reviewed and reworked their calculations to identify where they made an error in calculation or if the theory itself was fundamentally flawed. In addition, the nuance that allowed for the big bang in the first place relied on Einstein's "greatest mistake" of a fudge factor known as the cosmological constant to his general relativity equations.

In the meantime, a team of electrical engineers at Bell Labs were having problems explaining where a microwave interference signal was coming from. When they tested all of the equipment independently they proved to their satisfaction that the equipment was working as designed but whenever they pointed the antenna to any part of the sky. Eventually, these two teams found each other. The theorists' problem matched measured results to within resolution tolerances. The rest is history.

Simulated Annealing of Theory

I was casually aware of the Wilson and Penzias story complete with the pigeon droppings cutsie. Once again we are talking about conclusions in which I am expected to take on faith that the measurements could not be the result of some other phenomenon. I realize that I have not put in the work to review the calculations and that with such an effort I might be convinced. I have also been convinced that I had balanced my checkbook when I added something in error and later subtracted it in error. Again, I am not saying I KNOW they are wrong. It is just that the mechanism of looking at what is left from some universal set is one prone to false confirmation. The fact that Einstein and Hawking oscillated on Cosmological constants confirms, on the other hand, that this genre of errors is likely. Has the great nebulous THEY ceased oscillating or simply reached some local minimum masquerading as stasis ?

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thewildotter

If the latest news is correct, the big doughnut has been found 26000 light years away. Found in the Virgo constellation. It looks just like a big black hole.

https://www.theverge.com/2019/4/10/18303661/first-picture-black-hole-sagittarius-event-horizon-telescope

Anyone have any musings as to why the bright surrounding ring seems asymmetric ?

Do you suppose that the BH oscillates on the axis of the plane of the ecliptic ?

Or is it just that more stuff just happens at this moment to be approaching the black hole from the bottom of the picture? I wonder if the axis of the ecliptic is vertical in the image.

I see no obvious torus indicators so far. How frequently will they publish pictures ?

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thewildotter

My WAG is since the ejection jet is not aimed directly at us that it is obscuring part of the accretion surface. Remember, this is a 2D image of a 3D process. Unless our perspective is along an axis of symmetry it will appear to be asymmetric.

Earth(our perspective) is within the galactic plane of the ecliptic. Do we currently have an ejection jet ?

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thewildotter

As far as I know, the Milky Way galaxy does not have an ejection jet. If we did or eventually do get a jet it would be expected to be at right angle to the galactic plane due to the spin at the accretion disc. Thus it might be hard to detect our jet unless the jet interacts with dust to make a detectable spectrum. The Cygnus X-1 jets were detected with X-ray sensors above our atmosphere and showed that the jets varied considerably. Presumably, this is due to how much material gets consumed. The monster at our galactic core may not be feeding right now.

Oops! I missed that the black hole they are imaging is not the black hole at the center of our galaxy, the MilkyWay. Instead they are imaging the black hole in galaxy M87. Sorry about that.

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thewildotter

When I read Hawking's A Brief History of Time I do not remember his discussing the Olber's Paradox. However I would recommend reading it to anyone here. He discusses many of the topics we have mentioned in this thread, and much more. I found it technical but very readable.

--JMM