A parsec is a standard astronomical measurement that is often misunderstood.
What is a parsec? Definition and calculation : Read more
What is a parsec? Definition and calculation : Read more
The term parsec is NOT misused in Star Wars.
The point of the Kessel Run mentioned by Han is to find the shortest route by DISTANCE. Less time in hyperspace = less fuel and more profit.
It's the viewers who get it wrong, not the movie.
The "universal translater" accounted for that...Wait, that was the Star Trek universe. Never mind.Um, just how does an "intelligent being" in a galaxy "far-far away" at a time "long ago" know what a parsec is? Did they visit Earth and calculate it for themselves, long before humans invented telescopes?
Or, is it based on the parallax of some other planet orbiting some other star in that other galaxy, so that it has no known relationship to what we call a parsec?
Heck, even a light year would not match unless they happen to have come from a planet that also has a year that is 31,556,952 seconds long.
Wait, what are those alien guys calling a "second"? Maybe one 24th of one 3600th of the length of the day on their home planet?
Just a reminder of how Earth-centric all of our cosmological thinking is.
I went back and reviewed my copy of Allen's Astrophysical Quantities, Fourth Edition, c. 2000. On page 12, "2.3 General Astronomical Constants", the parsec is defined as 206264.806 AU (astronomical units). In meters defined as 3.0856776 x 10^16 m.
Defining H0 as 67 km/s/Mpc, space expands at 2.17131 x 10^-18 cm/s/cm. What happens to the value of the parsec now?
Is this based on the semi- major axis, or a fixed value like150E6 km. If the former, does the parsec get tweaked with better and better values for a?I went back and reviewed my copy of Allen's Astrophysical Quantities, Fourth Edition, c. 2000. On page 12, "2.3 General Astronomical Constants", the parsec is defined as 206264.806 AU (astronomical units). In meters defined as 3.0856776 x 10^16 m.
Local expansion, even for the parsec may take a long time before needing tweaked, I think. But I’m not convinced expansion overpowers any of the four forces, so nothin will change much in our galaxy until acceleration rates cause distance problems fir galaxies.Defining H0 as 67 km/s/Mpc, space expands at 2.17131 x 10^-18 cm/s/cm. What happens to the value of the parsec now?
I’m one who can’t seem to imagine how expanding space will overcome anything other than intergalactic space,when the force of gravity is very feeble relative to the expansion.That depends on how space-time actually expands (if there really is "Inflation"). If all of space is expanding the same everywhere, that is just the same problem of how to measure expansion with a meter stick that is also expanding - you can't. So, a parsec will always be a parsec, and a cm will always be a cm, as far as we can determine by measuring dimensions.
I wish I had time to answer this. *wink*. Perhaps if we learn more about time we can answer your good question,... And then there is the time part. Does it get stretched by inflation, or not?
I think there is no problem for the earliest moments of “pure” (Spock) energy. .But trying to think about it logically, if gravity can overcome inflation, then wouldn't the reason for "inflation" be lost for making the BBT work?
The atoms formed after 380k years, so the expansion speed at the atomic level was likely too wimpy to effect proton-electron orbits, IMO.So, how do you suppose that "space" can expand nonuniformly such that it does not change the spacing in atomic nuclei, electron orbitals, molecular bonds, orbiting planets, etc. but still can make all those things fly apart without going through "space"?
Nicely put.Remember, this is not the same as two forces pulling matter in opposite directions through space. There is an assumption that one force ("dark energy") works on space itself, changing its dimensions, while the other forces act on matter, but not space, and try to move matter through space.
There may be a correlation there, but Guth’s original hypothesis used a different mechanism for Inflation. DE was introduced to address the acceleration of expansion.Personally, I have my own doubts about the existence of "inflation" in the sense that the BBT requires it to work via "dark energy".
I had read one account suggesting space flows into a black hole, but Dr. Joe said otherwise, and his view is likely mainstream.On the other hand, I do think about how space behaves under intense gravitation, such as in the vicinity of a black hole. As I have asked here several times with no discussion in response: Does space just "warp" like a static lattice that can stretch but not shift in bulk, or does space "flow" more like a compressible fluid?
Ironically,SMBHs have a somewhat weak grav gradient that might allow close approaches in the distant future.If we could make a probe that could approach an event horizon, maybe we could tell which was happening. But, we can't do that.
I think there is no problem for the earliest moments of “pure” (Spock) energy. .
The atoms formed after 380k years, so the expansion speed at the atomic level was likely too wimpy to effect proton-electron orbits, IMO.
Right. Thus expansion of space does not have much affect on the other forces, except weak gravity areas between galaxy clusters.Even for atoms that formed 380,000 years after the BB, there has still supposedly been a factor of 1080 inflation of space since then. Surely, if that also expanded atoms and affected their electron energy levels, there is a problem with looking at redshifted hydrogen lines.
I suspect the strong force in the early microseconds would not be affected by expansion. Your H line example in the CMBR should be evidence enough, IMO.And, well before that, protons and neutrons were formed, and supposedly some alpha particles (helium nuclei). Wouldn't space dimensional differences affect the strong and weak nuclear forces' abilities to create stable nuclei and the energies involved?
I suspect they are seeing just what was expected, furthering the BBT.At this point, even the 380K years looks questionable, given that some astronomers think they are seeing older galaxies in the new Webb deep field picture.
IIRC, its age is in the margin of error. If not shouldn’t we have found many others by now. ~100 years ago, many stars were deemed older than the universe but this was due to Cepheid variations.And, there is also that "Methuselah star" that looks older than the 13.8 billion years that the universe has been thought to exist. See https://en.wikipedia.org/wiki/HD_140283 .
Perhaps this is so, but multiple lines of evidence supports the current model. Perhaps the best evidence is found in the time dilation effects in SN. The more distant ones will appear to last longer and be dimmer due to the expansion rate, matching the theory.So, maybe the cosmologic "dark age" didn't actually end at the age the BBT currently says. Maybe earlier? Maybe timing is off because time is not as constant as being assumed?
I don’t see this as ad hoc. The addition of Inflation theory, however, is sometimes held as ad hoc to fix two problems, including the anisotropy.It sort of amuses me when theoreticians start making assumptions to make their models fit other assumptions, rather than observations, as is the case with the BBT time line before what is assumed to be 380,000 year old light in the form of the microwave background.
The Big Bang Bullets thread presents objective evidence to greatly restrain suppositions.True that there is nothing else to fit if you have no actual observations. But, the logic of the interweaving of assumptions seems to be unconstrained attempts to make current thinking seem to be OK, without seriously exploring other potential ramifications of the added assumptions.
Yes, you’re hardly alone. Inflation theory looks at events that modern science cannot create in colliders, which are limited to t>1E-12 sec.To me, the concept of "inflation" raises a whole lot of questions about how we are interpreting actual observations. Theorists really can't have their simplifying assumptions without also raising complicating plausibilities.
I don't agree that modern science has created the conditions of the Big Bang after 10^-12 seconds, simply by slamming protons together and looking at the "pieces" that get created at high energies. There is a difference between two protons hitting each other at relative speeds similar to extreme temperatures in the early fractions of a second of the Big Band and the extreme density of such subatomic particles postulated for the condition of the whole universe at that point in time. All of the pressures, particle interactions, etc. are computed on the basis of theories that we can't really check for accuracy in those conditions. The idea that we "know everything there we need to know" about how subatomic particles behaved in the early universe seems not just uncertain, but unlikely to me.Inflation theory looks at events that modern science cannot create in colliders, which are limited to t>1E-12 sec.
Yep. I was hoping each bullet would bring further explanation, but it’s similar to how much we’re now not discussing parsecs.Helio, I did recently read through the BB Bullets thread, again. Not so easy with 7 pages of posts, now. So, no need to refer me to it.
Agreed, and I’m guilty as well, especially when an accurate value is not that important.I do have trouble with the media articles that play loose with the language regarding red shift, with z, 1+z and age all being mixed together, and not necessarily properly.
That’s not my impression. See this article.So, I tend to focus on estimated age values. Things like the Methuselah star don't fit. True, they keep trying to make it fit, and doing the "uncertainty band" dance, but the "best guess" value still doesn't fit.
The upper photosphere is ~ 5000K, and most of the hydrogen is H+. 3000K is the temp. when the vast majority of H is atomic. You might find this article interesting.Similarly, the cosmic background radiation supposedly having a black body temperature of 3000 Kelvins before 1080 times expansion of its wavelength by inflation seems to not match the current temperature where hydrogen ionizes in our sun's atmosphere (7,000 to 10,000 K). So, why did hydrogen not form until the universe had cooled by expansion to 3000 K?
Right, but they formed from atomic and diatomic hydrogen, plus helium etc. As the cloud collapsed, temperatures soared.Stars are made of plasma.
I think proton-proton impacts aren’t too fussy about pressures.I don't agree that modern science has created the conditions of the Big Bang after 10^-12 seconds, simply by slamming protons together and looking at the "pieces" that get created at high energies. There is a difference between two protons hitting each other at relative speeds similar to extreme temperatures in the early fractions of a second of the Big Band and the extreme density of such subatomic particles postulated for the condition of the whole universe at that point in time.
No theory can ever be proved, so it is always about the credibility of the theory and the objective evidence that supports it. There doesn't seem to be a lot of debate on a wide range of values for the age of the universe. Indeed, it was tweaked from 13.7 Byrs. to 13.8 Byrs. only a year or so ago due to better data.There seems to be some picking and choosing among estimates to make things "look right" with the theory. I just take that to mean that neither the theoretical estimates of the star's age nor the estimates of the universe's age are accurate enough to make the sweeping conclusions about exactly how things happened in the BBT.
That's interesting, especially given the solar upper photosphere is ~ 5000K (per Bhatnagar & Williamson), and I assume with a great deal of H ions, though even negative ions are present.Next, thanks for the link describing the theory about the equilibrium ratios of hydrogen ions to hydrogen atoms using the Saha equation and then some improvements. However, those results seems to be at odds with what is said in another link that I can't find at the moment, which gives values for roughly none to roughly 100% hydrogen ionization between 7,000 K and 10,000 K in our sun's photosphere.
That's a good question. I know that reionization produced more Thomson scattering, and this seems to have occurred at z ~ 7.7And, there is still the question in my mind about how the factor of 1080 inflation assumed for space could have affected the properties of hydrogen, including its ionization temperature.
I think cloud collapse models would struggle in producing progenitor stars from plasma given the need for some cooling, but I don't know.What observations make it clear that stars must start from atomic matter, rather than plasma. Is it even necessary for the BBT model to work?
The CMBR is uniform to about 1 part in 100,000, which is why it was so hard to produce the maps. This very little anisotropy was enough to produce stars but not for perhaps at least another 150 million years. These anisotropies, as I understand them, are dynamic, meaning these regions have cycles of contraction then, due to heating, expansion.How does the BBT show that no initial non-uniformities in the plasma could have caused stars and even galaxies to start forming before expansion to (average) universe temperature of 3000 K?
I confess to being very weak in particle physics, so I doubt I can be of much help. Nevertheless, it seems logical to me that what happens on an atomic scale would not require information on how close the neighboring atoms are, so I'm unclear just how density would apply, except on a macro scale.Finally, your comment that you "think proton-proton impacts aren’t too fussy about pressures," seems to ignore my point about using those impacts to try to produce some sort of equation of state for the extremely early universe. The particles produced by proton-on-proton impacts in the CERN collider are at infinitesimal fractions of their postulated densities in the first tiny fractions of a second following the Big Bang.
The claims by particle physicists seem to indicate a very strong understanding of what happened after the first trillionth of second, based on LHC experiments.So, how do you verify the theory about how those particles behave in such extremely dense concentrations?
They seem confident with knowing what was there beginning not long after quarks formed, partly due to the extreme success of the Standard Model, which predicted a number of new particles that were later discovered.Or, does the BBT ignore that physics question by postulating that some unknown force ("dark energy") produced "inflation" of "space" independently of what was in that space at the time, rather than because of what was in it at the time?