39 replies to this topic

[BillP]

That is the title of an article I just saw .  Talking about the ever growing discrepancy in measurements of the Hubble Constant and how we are unable to nail it down.  This of course leading to a realization that we may not understand things.

 

https://futurism.com...anding-universe

[sg6]

This of course leading to a realization that we may not understand things.

Not possible, of course we know everything there is to know.

We probably know everything about things we as yet do not know even exist.

 

Seems we have time travel here.

 

2 of our big science presenters are talking aboiut the days of the moon landing and their recollection of what it caused. Slight problem is they may have doctorates in Physics but they really should look at their date of birth (Wiki give both). Kind of impossible.

Edited by sg6, 16 July 2019 - 04:04 PM.

[J.LAMBIE]

"It ain't the things ya know that hurts ya. It's the things ya know that ain't so." Artemus Ward

[bobito]

"may be"?  I think we can use more certain phrasing here...

Edited by bobito, 16 July 2019 - 04:39 PM.

[BillP]

Not possible, of course we know everything there is to know.

 

I know.  And just when I thought the original Cosmos show was telling me facts.  And then the remake, Cosmos, A SpaceTime Odyssey, the way they presented like the "knew" things!  Now they can't even figure out their constants   Long Live Star Trek!!  At least there they tell you they are just "acting"!!

[jayrome]

Sometimes I get the impression that some very big assumptions get made along the way. Ok, I get it, its fairly easy to demonstrate that the Earth isn't flat, nor is the sky a fixed and unchangeable dome. And yet, with cutting-edge science you have to wonder, a lot of the scientific speculation really is at the mercy of technological limits and assumptions. Someone correct me if I'm wrong.

[ToxMan]

In theory, we got it right...

[EJN]

Well, the values are 67 (km/s)/mpc from the CMB, 73 from type Ia supernovae, and 70 from the new study, so it's not that big a spread.

In the 70's going into the 80's there was a 2:1 difference between various measurements, ranging from 50 to 100, so progress has been made.

What I think is that the error ranges of the various measurements are too optimistic, and the error bars really overlap.

These are all difficult measurements, so there is bound to be uncertainty.

"What do you mean that we can't measure this using an 80mm apo?"

Edited by EJN, 17 July 2019 - 01:18 PM.

[rockethead26]

So, what do the values 67, 70 and 73 each mean for the age of the universe? What's the spread?

[EJN]

About an 8% difference in the age of the universe, with lower values meaning older.

[rockethead26]

About an 8% difference in the age of the universe, with lower values meaning older.

Thanks. About 1 B years. Seems like a lot, but then you realize what they're trying to measure.

[DaveC2042]

A few thoughts from a non-expert with a bit of background.

 

First, remember the Hubble constant isn't really a constant.  It is an empirical measure, it changes over time, the proportionality it assumes is only established out to a certain distance (a few hundred Mpc), and a lot of assumptions go into any measurement of it, so it doesn't really have a well-defined value in the sense of, say, c.

 

Second, when error bars are shown for this kind of thing, they typically only incorporate a subset of uncertainties that are sufficiently well-defined to be mathematically analysed.  The more complicated (model-dependent, involving lots of measuring equipment...) the process is to calculate something, the more likely it is that the error bars are leaving out a bunch of stuff.  Physicists tend to know and understand this, and interpret accordingly, but it gets lost in translation to the wider public.

 

Thirdly, if there is a 'fundamental flaw' in our understanding, it is important to remember that this is only in relation to a particular regime.  None of this is going to overturn everything we know about relativity, quantum mechanics and statistical mechanics as they relate to the 'normal conditions' we experience here on earth, let alone any of the downstream science and technology (chemistry, biology, engineering etc).

 

Don't get me wrong, there is a real puzzle here and resolving it is likely to involve some fascinating new stuff, but sometimes the reporting of it gets a bit simplistic and overheated.

[EJN]

It's interesting to look at this compilation of measured values of Hubble's constant

posted by the late John Huchra of Harvard-Smithsonian Center for Astrophysics.

 

If you take the list of values published 1996 and later, and average them, you

get 68 (km/sec)/mpc, which just shows that if enough people measure something you

will eventually converge on a reasonably correct value. The list stops in 2010 because

of his death.

 

Look at some of the earlier measurements, the values are much higher than modern values.

 

In the 70's & 80's, Allan Sandage was consistently getting values around 50, while

Gerard deVaucouleurs was consistently getting values around 100. The

disagreements over these values became known as "The Hubble Wars."

 

Raw data here: https://www.cfa.harv...hubble.plot.dat

 

 

 

 

 

 

 

If Huchra were still alive he would call the current discrepancy a tempest in a teacup.

It is being totally overblown by pop-science writers.

Edited by EJN, 17 July 2019 - 10:48 PM.

[Jeff B1]

Steady State.

[EJN]

Steady State.

Steady state did not predict the cosmic microwave background, where as the big bang did.
When it was found, steady state faded away.

Fred Hoyle eventually came up with a theoretical mechanism to produce a cosmic microwave background
in steady state, but it seemed contrived and implausible.

Steady state cannot account for the observed amount of Helium in the universe either, where as
big bang nucleosynthesis does quite well.

Additionally, steady state requires the existence of a new
field called the C-field, which there is no evidence of from particle accelerators.

Invoking steady state is like biology going back to spontaneous generation, or thermodynamics
back to phlogiston.

Edited by EJN, 18 July 2019 - 12:48 PM.

[greenstars3]

"Invoking steady state is like biology going back to spontaneous generation, or thermodynamics

back to phlogiston." 

Or astrophysics going back to aether ( dark matter, dark energy)

 

Robert

[Geo31]

As I understand it, the Hubble Constant is simply a plug for something we don't understand.  Therefore, measurements yielding different, or changing, results are not surprising to me.

 

I sometimes shake my head at a lot of people who treat science as a constant.  The only constant is the change in our understanding of our world and the universe around it.

 

Dark Energy, again, as I understand it, is also a plug for something we don't understand.  Perhaps the next Einstein type will develop a theory that will tie up some loose ends in our theories and measurements (and probably lead to other loose ends).

 

How about "Dark Energy Stars?"  Strikes me as silly since Dark Energy is just a name given to something we don't understand.  Crackpot astrophysicists or brilliant thinker who can conceive what others can't?

 

https://getpocket.co...e=pocket-newtab

[Jeff B1]

"Invoking steady state is like biology going back to spontaneous generation, or thermodynamics

back to phlogiston." 

Or astrophysics going back to aether ( dark matter, dark energy)

 

Robert

It's almost like astronomers talking about astrology.  Both sides shake their heads and never bend.  Weird, not many astronomers know anything about astrology.  Hollywood does

[Mister T]

It's almost like astronomers talking about astrology.  Both sides shake their heads and never bend.  Weird, not many astronomers know anything about astrology.  Hollywood does

What is there to "Know" about ??

Knowing requires facts.

 

[DaveC2042]

As I understand it, the Hubble Constant is simply a plug for something we don't understand.  Therefore, measurements yielding different, or changing, results are not surprising to me.

 

I sometimes shake my head at a lot of people who treat science as a constant.  The only constant is the change in our understanding of our world and the universe around it.

 

Dark Energy, again, as I understand it, is also a plug for something we don't understand.  Perhaps the next Einstein type will develop a theory that will tie up some loose ends in our theories and measurements (and probably lead to other loose ends).

 

How about "Dark Energy Stars?"  Strikes me as silly since Dark Energy is just a name given to something we don't understand.  Crackpot astrophysicists or brilliant thinker who can conceive what others can't?

 

https://getpocket.co...e=pocket-newtab

Sort of.

 

The Hubble Constant is a measure of something very real and fairly well understood.  The universe is definitely expanding, and this is definitely a 'stretching' of the fabric of space-time and not simply things in the universe flying apart from each other.  The HC is simply a measure of how much expansion there has been.  The exact value of the HC is a bit problematic, firstly because it's not really a constant (it changes) and secondly because it is very difficult to measure accurately, and doing it different ways gives different results, for reasons we don't fully understand.  But the results are not so different as to suggest a resolution is simply impossible.

 

Dark Energy you have a better point on, but even there, we understand more than nothing.  We've measured the expansion of space-time, and it appears to be accelerating - that is a real thing, an actual observation requiring explanation.  Dark Energy can be thought of as a label for whatever is causing this.  Now it is worth understanding that the observed accelerating expansion is not the only thing suggesting there is Dark Energy - cosmologists also need it to explain the flatness of the universe, and some aspects of mass distribution within it.  So part of the strength of the hypothesis is that it has multiple lines of support.  That seems to me to be a lot more understanding than none.

 

Finally, I wonder if this is a bit of a strawman.  This is a very active area of current research.  No one is suggesting we do understand it all.  If we did, there would be nothing to research, and wouldn't that be boring.

[greenstars3]

"No one is suggesting we do understand it all.  If we did, there would be nothing to research, and wouldn't that be boring."

 

Yes. Yes it would, its the mathematical "fix" of dark matter/energy that has no place in particle accelerator artifacts or observational reality that makes it suspect.

 

Robert

[Jeff B1]

What is there to "Know" about ??

Knowing requires facts.

 

Maybe.  We look at astrology as some weird Hollywood religion, but in most news publications a lot more is written on astrology than astronomy, so when someone presents arguments for it then the counter arguments should be with some knowledge of the opposing side's "facts."  I met George Abell many years ago and he gave a talk on why he studied astrology.  He was constantly bugged on TV appearances about the difference between astrology and astronomy then found himself ignorant of astrology.  So he set out to learn about it to debunk it whenever he could.

 

George's talk was very interesting in that he taught us how to understand astronomy as well as how to offer counter arguments to astrologers without causing a fight.  While it may seem futile, he made good points on how not to make people hate us for pointing out that astrology was a waste of time.  No one likes to be told that.  He pointed out that a lot more people believe in such hokum than we know.  

Edited by Jeff B1, 31 July 2019 - 05:49 AM.

[Jeff B1]

For most of my life of engineering, science and mechanics I lived in a bubble with mostly similar people around me, so after being retired for so long and having outlived so many of the old astrometry gang it can get quite interesting when conversing with “normal” people.  I find myself having to explain every aspect of astronomy to people that have virtually no knowledge in astronomy, or more often distorted understanding with science in general that explain it becomes quite difficult to do in simple terms.  Just the basics can be challenging for those friends that lack the education and knowledge in science.  At times it I easier to just not say anything about it; however, it is hard to hide from your background very long.  So, one either learns how to speak in simple terms to new friends or find yourself outside their bubble.

[llanitedave]

There's nothing wrong with knowing the conceptual details of a non-scientific field of belief.  That's why I made a lot of effort to study the beliefs and arguments of creationists many years ago.  That doesn't mean those arguments are not hokum.  It merely allows you to understand exactly where they fall short.  True, nobody likes be told that cherished beliefs are a waste of time.  That doesn't make them any less of a waste of time, though.  I knew lots of people who didn't like to be told that smoking would kill them.  Some of them are dead now.

[Jeff B1]

There's nothing wrong with knowing the conceptual details of a non-scientific field of belief.  That's why I made a lot of effort to study the beliefs and arguments of creationists many years ago.  That doesn't mean those arguments are not hokum.  It merely allows you to understand exactly where they fall short.  True, nobody likes be told that cherished beliefs are a waste of time.  That doesn't make them any less of a waste of time, though.  I knew lots of people who didn't like to be told that smoking would kill them.  Some of them are dead now.

Yeah, several of my closest friends assumed room temperature from lung cancer.  One was a doctor, a gas-passer and respiratory specialist, who smoked like a coal fire power plant.  After I stopped smoking  40 years ago I bugged him to stop right up to ten minutes before he expired.  He was one of the few real geniuses that mixed medicine, music, humor, astronomy and telescope making, and was a pioneer in imaging. I guess my arguments against smoking were not convincing enough.  Now they are all gone, but me.  Why?  

 

I never argue about religion and such, but interested in what people believe.  I can justify hating back holes because no one will ever observe what makes them work, at least from inside one.  That doesn't mean black hole science is wrong or will stop anyone from doing it.   I like steady state because some of it fits what we observe.  I love to study clouds on Mars, but will never go there to see them up close.  Just assume those who taught me about them were not crazy.

Edited by Jeff B1, 31 July 2019 - 01:13 PM.