astro123

I don't know why this is downvoted (maybe I'm missing a bad joke)? But this is exactly why people are excited about this. Either,

a) we have a systematic in our measurement and our model is right and eventually we'll work this out when we fix up everything, or

b) our model isn't right and there is new physics (i.e. something not in Lambda CDM + GR) that explains this discrepancy.

Nope, that's total garbage. H0 is defined as the rate of expansion now.

Yeah, I'll second what others have said that designing (good) telescopes is not a quick/easy thing. Also, any telescope that is easy to slap together is probably so many orders of magnitudes worse that existing ones that you don't get any usable data from it.

I'll throw a couple examples out for you:

DESI[1] has 5000 individually movable fiber optic cables. It's also sitting on a 4m mirror. It is a massive engineering project, but also would make anything with similar goals that a handful of people could hack together for a few million dollars obsolete. It can get 5000 spectra every 15 mins and a small, slit based telescope can maybe do a handful per night. Large scale projects like "mapping the night sky" are going to be dominated by massive projects. See also GAIA [6]

Space based makes things way harder. Let's take JWST[2] as an example. Someone else has mentioned the tolerances on the mirror. You also need to keep everything cold (7 kelvin!). You need to be able to control this, keep it pointed in the right direction with stunning accuracy, etc, etc. And all this needs to work in space, after being shaken around through a rocket launch. You also need a really compelling reason to go to space for a telescope. Those reasons include, observing things that you can't see from the ground (X-rays for example). You need really good seeing (no atmosphere). You need really low noise observations. I'd be surprised if those were what a small operation needed. Especially when it makes all the other things (control, servicing, etc) so much harder.

In fact, there are gaps where pretty simple ground based hardware can do good scientific work. Though, it is usually for pretty specific goals. [3] is a bunch of DSLRs that is one of the best instruments for finding really diffuse galaxies which are really interesting systems at the moment.

On the ML techniques, those are definitely being used in astronomy. One recent example [4] but go to ADS and look for things with ML in the title and you'll get a lot.

[1] https://www.youtube.com/watch?v=g1LVMox0KNc [2] https://jwst.nasa.gov/content/observatory/ote/mirrors/index.... [3] https://www.dragonflytelescope.org/ [4] https://www.kaggle.com/c/PLAsTiCC-2018 [5] https://ui.adsabs.harvard.edu/search/filter_database_fq_data... [6] https://en.wikipedia.org/wiki/Gaia_(spacecraft)

I think that [1] is the paper that this is based on. I don't work on dynamics and I found it pretty readable. Most of what is in the article is in sections 3.2, section 4 (discussion) and section 5 (conclusions).

[1] https://arxiv.org/pdf/1904.11436.pdf

Not to go into much detail, but these author's views are not shared broadly in the cosmology community. There was a recent paper [1] put on the arxiv that talked a bit about this. I'm not an expert on supernova cosmology (I work on cosmology using other methods) but people I know who are experts claim there are issues.

There are also a ton of other reasons to think that the universe is flat (see the CMB [2]) and to think that there is dark energy (large scale structure [3]).

We still have no idea what DE is and it might not be an "Energy" but rather some modification of gravity or something else. But we're pretty confident in the phenomenology - there is something there that appears to be pulling things apart.

[1] https://arxiv.org/pdf/1911.06456.pdf [2] https://physics.stackexchange.com/questions/439535/why-does-... [3] https://www.darkenergysurvey.org/supporting-science/large-sc...

The paper is https://arxiv.org/pdf/1903.12097.pdf for anyone interested.

The results aren't actually that interesting. The posterior on H0 (the rate that the universe is expanding) is not at all competitive with the current best methods. They get 67 +/- 6 whereas things like Planck have error bars on the order of 1. Checkout their figure 5 to see the different error bars.

That is not to say the paper is bad at all! The method they use is pretty cool and not common (at least I haven't seen it used before, though they do mention there have been people looking at this for a while). Also, as the main source of concern for cosmologists is systematic errors, having multiple ways to measure things is very important. They call this out in their intro, "As discussed by Suyu et al.(2012), multiple paths to independent determinations of the Hubble constant are needed in order to assess and control systematic uncertainties"

I'm not sure this is a great general interest article as AFAICT there are no big picture take aways from the paper. Again, this is not to say that it is not a good paper - I found it pretty interesting! - but the cool parts are that this is a good measurement of H0 using a less common technique.

One weird thing about the article is

> In a paper published Friday, Nov. 8, in The Astrophysical Journal, Clemson scientists Marco Ajello, Abhishek Desai, Lea Marcotulli and Dieter Hartmann have collaborated with six other scientists around the world

I see the article was written by someone at Clemson, but it is a bit odd in a non-Clemson publication to explicitly call out a bunch of secondary authors, and not mention the primary author until much further down. In general in astrophysics, the vast majority of the work (except in very large collaboration papers) is done by the first author.

This is exactly the sort of thing that blinding is there to prevent. It is the same reason we in cosmology blind our data - to prevent us from biasing ourselves towards what other experiments have found.

Also, the charge of the electron experiments you are talking about happening over 100 years ago, so not that relevant to today :)

With the caveat that I have nothing to do with ligo and so don't know much...

I think that during this ligo run (it just turned back on in April-ish) they expect to find roughly 1 event per week. So this will be fairly common! [1] is a nice summary of what they have found so far.

For people here interested in the engineering side of LIGO, it is absolutely mind blowing. The effect of the gravitational waves is tiny (fractions of the size of a proton change in length) and so there are so many things that need to be incredibly tightly controlled for. I went to a talk on this a year or so ago, but can't find the slides... Here's a summary [2] and the wikipedia page also has some info.

1 - https://www.sciencenews.org/article/ligo-virgo-made-5-likely... 2 - https://www.engineering.com/Education/EducationArticles/Arti...

Here's a statement [1] by one of the largest upcoming surveys, LSST. At least for them, this isn't going to be too much of a problem as,

1) Exposures are fairly short and frequent and so pixels contaminated by these satellites can be easily rejected. 2) There is a huge amount of resources (relative to other projects) going into the image pipeline for this project.

I don't actually know in details how much this will affect other types of observations though. [2] is the IAU's statement (that goes with that image), which points out some types of observations that might be more affected.

[1] https://www.lsst.org/content/lsst-statement-regarding-increa... [2] https://www.iau.org/news/announcements/detail/ann19035/

As the article mentions, this is most likely due to the rotation of the cluster. Throwing some numbers out there:

The Virgo cluster is 60Mly away which is ~20Mpc (mega parsecs). Hubble's law [1] (v = Hd) tells us that for every 1Mpc away an object is, the expansion of the universe causes it to move away from us at about 70 km/s. So 20Mpc -> 1400km/s.

The true velocity is actually about 300km/s less than this because the local group is being pulled gravitationally towards Virgo. (If you are interested, this movement of the local group towards Virgo is the largest component of the earth's motion relative to the CMB. Some of the others being the earth's motion around the sun and the sun's around the milky way).

The velocity dispersion of large clusters is known to be on the order of 1000 km/s, so its not surprising that one or two objects whose orbits happen to be bringing them towards us are net blueshifted.

The long and the short of it is that this is more of a cool curiosity than evidence of something crazy going on.

[1] https://en.wikipedia.org/wiki/Hubble%27s_law

The full story is actually (I think) more interesting than the headline suggests.

Really what we have here are two methods of calculating the age of the universe that disagree. And we are getting to a stage where the disagreement (or "tension") is fairly statistically significant (3 or 4 sigma if I remember correctly). But, if LambdaCDM is the correct model for the universe these two methods should give the same age and so the fact that they are different implies that there is more to the universe (new physics!) than LambdaCDM. This is very exciting (and imo much more exciting than a 10% change of the age of the universe)!

Of course, both sets of measurements are fantastically hard to make and so there is a chance that this disagreement is just a result of a systematic that hasn't been properly understood/controlled for... But people are starting to think this might be real.

Here's a readable summary of what's going on: https://astrobites.org/2016/08/22/the-trouble-with-h0/

I was maybe a bit too cavalier here. I think I understand what the author means - the data that they gather is understood in the context of the model that we think is best.

But, it isn't as if cosmologists are rigidly holding to the model. Here's a paper looking at extensions to lambda CDM https://arxiv.org/abs/1512.05356. As I mentioned, changing GR is being looked at as an alternative to DE http://www.resceu.s.u-tokyo.ac.jp/workshops/resceu08s/presen...

People aren't challenging some things though - I don't think anyone is seriously working on cosmologies that don't include a big bang, because without one I can't imagine how you explain the CMB.

For some reason edits are silently failing, but an addendum to

> Big bang was only the accepted paradigm from the 60s (post CMB observations). We have had DE since Einstein in 1917 and DM since Zwicky in the 30s.

Admittedly the DE from Einstein is for very different reasons than the DE today, but we again had the big bang and no DE from the 60s until the 90s (observations from https://en.wikipedia.org/wiki/Supernova_Cosmology_Project) so they don't go hand in hand.

I'm a grad student working on cosmology, and while I agree there is a lot of work still to do (we don't know what 95% of the matter that makes up the universe is!), I disagree with a lot of what the author says.

> Another recent probe found galaxies inconsistent with the theory of dark matter, which posits this hypothetical substance to be everywhere.

We have found evidence of a few galaxies without DM. But most galaxies provide strong evidence for DM - https://en.wikipedia.org/wiki/Galaxy_rotation_curve

> For a crucial function of theories such as dark matter, dark energy and inflation, which each in its own way is tied to the big bang paradigm

Big bang was only the accepted paradigm from the 60s (post CMB observations). We have had DE since Einstein in 1917 and DM since Zwicky in the 30s.

> Historically, Newton's physical laws made up a theoretical framework that worked for our own solar system with remarkable precision. Both Uranus and Neptune, for example, were discovered through predictions based on Newton's model. But as the scales grew larger, its validity proved limited.

Actually some of the earliest evidence for GR came from the orbit of mercury https://en.wikipedia.org/wiki/Tests_of_general_relativity

> It is of course entirely plausible that the validity of general relativity breaks down much closer to our own home than at the edge of the hypothetical end of the universe. And if that were the case, today's multilayered theoretical edifice of the big bang paradigm would turn out to be a confusing mix of fictional beasts invented to uphold the model

This is something that people are working on! This is a hypothesized source of DE. However, disproving GR does nothing to disprove the big bang.

> Today's space telescopes provide no direct view of anything

I have no idea what that means. They literally observe the sky...

There is a ton of work to do: finding what DM is, finding what DE is, finding whether GR is correct. But I'm not sold that the author knows what he is talking about...