I Discrepancy in the Hubble Paramater

[Haelfix]

It is expected that future LIGO/VIRGO measurements will over time (say a decade), be able to arbitrate between these competing stories.

 

[alantheastronomer]

I understand your confusion Windy, two different values for the Hubble constant should result in two different ages for the age of the universe. The supernovae study found something very interesting however; it discovered that the expansion of the universe is accelerating as time goes on. This means that the universe was expanding slower at earlier times. If we use the present day value of the Hubble constant to calculate the age of the universe - the accelerated value - then we'll underestimate the age of the universe because the universe was expanding slower earlier on.
I'm sorry, I don't have a calculated value for the age of the universe for you. For that I think you'll have to look for publications by Adam Reiss.
The values you mention, 68 and 71, while not in agreement are much better than the way it used to be. Before, the discrepancy used to be between 50 and 100!
This is because, while both used the cosmological distance ladder to reach their conclusions, they disagreed on one crucial factor; the distance to our nearest neighbor - the Andromeda galaxy. This galaxy is located near the plane of the Milky Way in the sky and so it might be dimmed by dust in the plane of the Milky Way. This dimming, by the way, is called "extinction". deVaucolours, who championed a value of 100 for the Hubble constant, didn't use any extinction, and so estimated a distance that was further away because it was dimmer. Sandage on the other hand tried to compensate for the dimming due to dust and got a closer distance to Andromeda. A closer distance means a slower expansion, and his value for the Hubble constant was 50.

 

[Orodruin]

If we use the present day value of the Hubble constant to calculate the age of the universe - the accelerated value - then we'll underestimate the age of the universe because the universe was expanding slower earlier on.

This is, at best, misleading. In a flat universe containing only a cosmological constant the Hubble constant is just that, a constant. In our actual universe, the Hubble rate is actually decreasing. As has already been stated in this thread, to find the age of the universe you need to solve the Friedmann equations backwards for the actual composition of the Universe.

The values you mention, 68 and 71, while not in agreement are much better than the way it used to be. Before, the discrepancy used to be between 50 and 100!

Again, as has already been stated, that the values are closer does not mean that the discrepancy is worse. You have to look at the error bars relative to the discrepancy.

the distance to our nearest neighbor - the Andromeda galaxy

The Andromeda galaxy is within our local cluster, which is a gravitationally bound structure. It is not affected by the expansion.

 

[alantheastronomer]

I wasn't saying that the Andromeda galaxy is affected by the expanding universe; it is a crucial part of the cosmological distance ladder that caused the large discrepancy in the two values found for the Hubble constant that is a part of the history of science.

 

[alantheastronomer]

I never said that the discrepancy was worse the closer the values were.

 

[Orodruin]

I never said that the discrepancy was worse the closer the values were.

I will buy that you did not explicitly say that Andromeda is affected by expansion, although it may be read that way. However, I can see no other interpretation of this:

The values you mention, 68 and 71, while not in agreement are much better than the way it used to be. Before, the discrepancy used to be between 50 and 100!

than you claiming that the discrepancy used to be worse because the values are further apart. There is absolutely no reference to error bars.

 

[StandardsGuy]

You are ri

You are right I initially posted the wrong values I have now corrected this. But I don't see what the relevance is to the question. the question was do the different value of the Hubble parameter mean we should have two values for the time since the big bang? We've had more than a dozen posts in this thread now and no one has actually given a clear answer answer to the question in hand. Perhaps then you can see why someone gets frustrated by side shows like these. And i agree physics forums is excellent. But that doesn't mean there aren't cases of unnecessarily distracting the conversation or that things can't be improved. You didn't provide a reference that physics forums was 18 years old. since the numbers you initially stated were wrong! the forum was founded in 2001. here's a reference for you :
https://www.physicsforums.com/help/aboutu
Now the reference i have only gives us the year of founding: 2001 . it might have been dec 31 2001 for all i know in which case it is more like 16.2 years old. Which is further out on a percentage basis that I was on my values for the Hubble. Perhaps you can see how this sort of pedantry can get frustrating and waste people times?

Dont get me wrong I am all in favour of providing references. But there are cases when these are required and cases when they are not. to ask for the reference and pick apart your mistake about the age of physics forums is pedantry and I am doing it as a satirical way of making a point. . the truth in the point you make isn independent of wether the forums 18 years old, or whatever. So to focus on it is just silly. Same with my questions. To focus on the values of Hubble or even the sigma is to miss the point of the question. . of course we should correct false information but to do so without answering the questions in hand is just annoying. I think if someone asks a simple question on a forum about something that has been widely reported and not disputed then it would be simpler and easier to just answer the question. something I'm still waiting for.

On the 2 sources you named with their uncertainties, my answer is that one or both stated their uncertainties too small.

 

[alantheastronomer]

Orodruin - You're right, I did mean to imply that the discrepancy was worse in the past. The error for both values were around plus or minus 15%, certainly not big enough for the values to overlap, which I suspect you were hinting at... The disagreement in the Hubble constant (by a factor of two)translated to, by naively taking the inverse of the Hubble constant to be the time since the Big Bang, a difference of 10 billion years for a Hubble constant of 100 and 20 billion years for a Hubble constant of 50. Researchers tended to favor the value of 50 over the one of 100 because ten billion years is less than the age of the oldest stars, and that is contradictory.
In the past, before the advent of space based observatories, ccd detectors, and adaptive optics, astronomy was a notoriously inexact science. In fact, in many publications you'd frequently find error bars that exceeded the observed values! Researchers would "massage" the data to find useful science nonetheless. The cosmological distance ladder doesn't start with the Hubble flow, it begins with finding the distance to the nearest stars using parallax. The distance to the Andromeda galaxy is critical because it is used to calibrate the absolute magnitude - frequency relation for Cepheid variable stars, which is then used to find the distance to farther galaxies. The frequency in that relationship refers to how rapidly the stars' luminosity changes, the brighter the star the more rapidly it oscillated.