In past posts, when I’ve written about the expansion of the universe, I’ve generally referred to the rate of that expansion, the Hubble constant, as being around 70 km/s/megaparsec, that is, for every megaparsec a galaxy is distant from us, it’s moving away at 70 kilometers per second faster. So a galaxy 100 megapasecs away is moving away at 7000 km/s, and one 200 megaparsecs away at 14000 km/s.
But I have to admit this was an oversimplification. 70 km/s was actually a rough and rounded averaging of two measurements for the expansion, one taken using the cosmic distance ladder, and the other using observations of the cosmic background radiation. The former currently yields about 74 km/s, and the latter about 67 km/s.
Everyone for a long time thought this difference was just a measuring artefact that would eventually be smoothed out. Everyone is turning out to be wrong. As this news story discusses, the two measurements have been refined extensively. Confidence in these individual measurements are pretty high, and the margins of error don’t overlap.
In other words, either one or both of these methods has assumptions in it that are wrong, or there is something completely unexpected going on in the universe that cosmologists haven’t yet accounted for. For most scientists, this is a reason for excitement. This kind of issue typically leads to new insights.
However, it’s led to a debate that someone has been asking me to comment on. Bjorn Ekeberg, a philosopher of science, has focused in on this problem, along with others, to assert that cosmology has some big problems, calling into question the overall big bang cosmology. This drew a response from cosmologist and science writer Ethan Siegel pushing back against Ekeberg’s claim and accusing him of being anti-science. Ekeberg has responded accusing Siegel of being a “temple guard” for big bang cosmology.
Name calling aside, who’s right here? Not being a professional physicist, or knowledgeable enough to read raw physics papers, my comments are inevitably based on what various science writers have provided.
But in considering Ekeberg’s position, it’s worth reviewing the evidence for the overall big bang model. Physicists in the 1920s figured out that, under general relativity, the universe could not be static. It had to be either expanding or collapsing. If it was expanding, it was smaller yesterday than today, and smaller the day before. Following that back led to a period in the past where everything was all bunched up together, very dense and very hot. The physics of the early universe could be mathematically deduced and predictions made. (This led Einstein to fudge his equations a bit by adding a cosmological constant, making the universe it predicted static.)
Then in the late 1920s, Edwin Hubble discovered that the light from every galaxy beyond a certain distance was red shifted, with the amount of red shift being proportional to the distance. Red shift is a doppler effect that happens when something is moving away from the observer. Hubble had discovered that the universe is indeed expanding. (Einstein concluded that the cosmological constant was his biggest blunder.)
Still, cosmology was slow to just accept the big bang model. (It didn’t help that Hubble’s early estimates of the age of the universe had it younger than geologist estimates of the Earth’s age.) It continued to be debated for decades, until the discovery of the cosmic background radiation in the 1960s, which provided evidence for the calculations of the physics of the early universe. That was enough for most cosmologists. The big bang became settled science.
As a lay person, reading this through the translations of the experts, classic big bang cosmology seems pretty solid. I think Ekeberg, by implying it isn’t, oversells his thesis. But it’s worth noting that this settled version doesn’t get into what caused the big bang in the first place.
Ekeberg also has issues with the ideas of dark matter and dark energy. My understanding of these terms is that they’re essentially place holders, labels for our ignorance. So criticism of them as theories has always struck me as premature.
The most often touted alternative to dark matter is MOND (modified Newtonian dynamics), but no simple modification to the equations seem able to account for all the observations. Whatever is causing the rapid rotation of galaxies and other intergalactic effects seems to require something that is present in varying densities or intensities. Dark matter may eventually be so different from matter as we understand it that the word “matter” might not be appropriate, but until then, the term really just refers to something mysterious causing varying gravitational effects.
This seems even more true for dark energy. The fact that, against all expectations, the expansion of the universe is actually accelerating rather than decelerating, has to be caused by something, some form of unknown energy. (Ironically, dark energy has resurrected Einstein’s cosmological constant.)
Granted, it does seem unnerving that this results in 95% of the matter and energy in the universe being unobservable and unaccounted for. It’s easy to take this number and other measurement issues and accuse cosmologists of not knowing what they’re doing. Easy, but I think facile. The widely accepted theories that we now have are grounded in observation. Anyone is free to propose alternatives, but to be taken seriously, those alternative have to account for at least as much of the data as the current theories.
I do think one area where Siegel is overconfident is cosmic inflation. I’ve written about the concerns on this before. Some version of inflation might turn out to be true, but I think his stance that it’s a settled issue isn’t justified yet. And the fact that a significant portion of physicists are starting to question inflation, including some of its earliest supporters who now say it generates more issues than it solves, should make the rest of us cautious in our stance toward it.
So, does cosmology have issues? Of course, and Siegel admits as much. But is the overall big bang cosmology model in crisis as Ekeberg seems to contend? I think this is vastly overstating the issues. But only time and the data will tell. Of course, this controversy will likely lead to more sales for Ekeberg’s book.
What do you think? Is the overall big bang model in trouble? Or is this just about fine tuning the details, such as the age of the universe? If it is in trouble, what might replace it?
SelfAwarePatterns 
These situations come about fairly often in science. I am not concerned as to how it all falls out (something needs to be different) in that we all are committed to using settled science … until it stops working. Then we hash out what does work and keep going. This does not bother me. What bothers me are scientists (of which I am one) who rush out claiming that they know what’s what or worse that “the sky is falling.” Humility, apparently, is out of fashion.
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Humility never seems to be around as much as it should.
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I like to think our alien zookeepers just didn’t get the fake universe backdrop quite right. After all, they’re on a budget and can’t afford the best artists for a background for mere animals! 😀
Slightly more seriously, supposed putative evidence we live in a virtual reality is said to be “errors” in reality, so … #justsaying 😉
Completely seriously, it’ll be interesting to see how this shakes out. As you mentioned, the error bars don’t overlap and confidence is high in the measurements. It reminds me of the QFT versus GR conundrum. Great evidence on both sides, but … something’s gotta be not quite right (if not plain wrong).
Which, I think to your main question, suggests there may be things not quite right with the BB model, but that’s not to say it’s completely wrong. You know I’m not a fan of Siegel — noticed, but didn’t read, the post you refer to — and I do think there are a lot of assumptions involved. This may just be a batch of FTL neutrinos.
I’ve always been a little skeptical that we clever apes have really sussed out how the universe started 14 billions years ago. (I just saw a headline for an article challenging the age by a billion years or so.) I think there is a conceit in thinking we’ve got it all figured out from down here on our little rock.
I think it’s very likely we’re still blind men trying to figure out this weird snake-tree-leaf-wall thing. There’s a lot more to this elephant.
(re Dark Stuff, I tell people to just replace both phrases with “we have no idea” and be done with it. As you say, “placeholders.”)
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Somebody on Twitter asked for people’s conceptions of God. One that sprang to mind was aliens tinkering with a universe simulation. Maybe they’re running too many and ours isn’t receiving the attention it deserves.
I actually don’t read Siegel nearly as much as I used to, although I’m still subscribed to his feed and occasionally scan the titles. I actually had missed that particular post, and Ekeberg’s for that matter, until someone called my attention to them.
On FTL neutrinos, if this turns out to be just a loose communication cable somewhere, I think a lot of people are going to be, to quote Prince Humperdinck, “quite put out.”
On that headline, yeah, that’s the last link I provided in the post. That article points out that if we take the cosmic distance ladder measurements at face value, the universe is only 12.5-13 billion years old, shaving at least 800 million years off what everyone took to be a rock solid measurement. How embarrassing if true. But as you note, it’s still the big bang.
The one thing we can say about reality is that it will surprise us.
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I must be an idiot, because I can’t figure out why this data couldn’t be explained by positing that the matter at the CMB time was already moving away from each other with a relative speed that depended on distance. Would that change the redshift of the CMB in ways that exactly cancel the effect on light from stars?
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I have to admit I don’t really understand how the CMB measurement works, using Planck or any similar survey. Something to do with temperature and frequency. I haven’t been able to find an intelligible description of the methodology. So no idea.
I do have a decent understanding of the cosmic distance ladder one (parallelax, Cepheid variables, Type 1A supernovae, etc), although it’s dependent on a chain of measurements any of which, if wrong, can throw off its final result, and it’s the one that might lead us to conclude the universe is only 12.5-13 billion years old.
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I guess if hydrogen was in motion at the CMB time we wouldn’t see uniform temperature, we’d see a systematic redshift. So it would have to be dark matter that had the motion, while hydrogen was at rest (relative to neighbors). That would be pretty weird I guess.
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I think the matter at the generation of the cosmic background was definitely in motion. The universe had already been expanding for 377,000 years, according to the standard predictions.
The issue with talking about redshift with the CMB, is that the reason it’s the cosmic microwave background is that it’s been stretched (redshifted) throughout the history of the universe into the microwave band.
Maybe that’s how the CMB measurement works, comparing the predicted spectrum generated by recombination with the current spectrum of the CMB, in other words, the redshift. If so, I wonder if there could be any uncertainty in the predictions of what recombination should have produced.
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Huh. The CMB happened when the optical density of the universe went from near 1 to near zero. Presumably that would be slightly different time stretches in different places; after all there had to be some anisotropy to go along with the slight variations in CMB temperature. In which case, maybe something could be learned about relative motion of non-dark matter at those times.
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Mike .. fon’t forget also the entry of the famous professor who led me to extreme despair.
—–
First quantum mechanics, now cosmology. Scientific American’s blog has become a welcoming space for complete nonsense. sc
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Ah, I did forget about Sean Carroll’s tweet. Unfortunately, I have to agree with him to some extent. Scientific American is currently letting a distressing amount of nonsense get posted on their site.
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Of course one can agree – so that only professor sc himself didn’t write stupidity.
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Their descent into populism is why I stopped subscribing quite a few years ago!
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Mike. “sA is currently letting a distressing amount of nonsense get posted on their site”.
and this .. is it serious: mini universes could be constantly exploding at every point in space. New Scientists.
Reality on almost all science websites.
or maybe I’m wrong?
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I don’t really read New Scientist. Too much of their stuff is pay walled. (SciAm gives you a limited number of free articles per month, but it’s trivial to defeat their counter.)
Every science news site has at least an occasional blunder in their quality control, but it seems like SciAm’s fail rate has been higher than normal lately. I still get good info from Cosmos, NPR, The Conversation, BBC Future, Science News, and The Atlantic, among others.
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We shouldn’t rely upon incorrect assumptions associated with the observations of the cosmic background radiation, when computing the Hubble constant. I think that there was no Big Bang. I think that the situation will only be resolved, when we realize that the infinitely-old universe is infinite and everywhere expanding, with respect to both matter and space. New finest fundamental particles come into being, when they temporally come into being in light and are say pulled down by the discrete electric fields within the energetic gravitons so that the particles then remain. The new matter comes along with the new space that contains the new matter. The new matter is the basis of the so-called dark matter. The new space is the basis of the so-called dark energy. Such a viewpoint also solves the previously unsolved problem of how the most energetic cosmic rays are obtained. These kinetic-energy-unbounded particles are produced within truly cosmic or infinite size accelerators from less energetic cosmic rays, which cosmic ray particles absorb more attractive gravitons in front of them than in their rear. See more details in my book Gravity-Wheel Unveiled, which you may obtain a free .pdf file of (from https://gravityunveiled.home.blog/). AEP – 21 May 2019
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That’s a pretty radical view. Maybe it’s right, but you’ll have to convince working physicists that your models account for all or more of the observations than the current ones do.
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My current approach, to attempt to convince working physicists, will be to first show that I have the correct model for discrete gravity, by the large number of evidences for the Bessler principle. The Bessler principle provides greater energy for wheels of any size rotating about horizontal axes. I am aware of no other model or theory that predicts it. There are at least 37 separate subject areas in my book which provide evidence for the Bessler principle. The Bessler principle thus provides a vast amount of evidence for the two-part graviton or that each graviton has two separate pull-downs. I also provide a large number of different types of experimental tests. I figure that the experimental/observational/testing approaches may be best for persuading working physicists. Either there is or there isn’t a Bessler principle and if the physicists don’t just ignore the great amounts of evidence for it, then they should be convinced of its reality. If we don’t have the correct theory for gravity with respect to things that we can measure, how can we expect to determine the correct things in the cosmos with respect to gravity?
Newton effectively spoke of rays of discrete gravity, when he wrote according to my transcription of his words, “Whither ye rays of gravity may bee stopped by refecting or refracting ym, if so a per petuall motion may bee made one of these two ways.”
Einstein wrote to his good friend Michele Besso in 1954 “I consider it quite possible that physics cannot be based on the field concept, i.e. continuous structures. In that case nothing remains of my entire castle in the air, gravitation theory included, [and of] the rest of modern physics.” I think that Einstein was prepared to give up his own theory of gravity in favor of purely discrete theory.
In hindsight, shouldn’t we have seen the discrete nature of gravity that Newton hinted of (and that Einstein appeared to be prepared to embrace) since we now know that both the gravitational fields and the electric fields roughly fall off as 1/(r*r) = 1/(r^2)? The fields don’t just get weaker infinitesimally as we are further away from their source, without any sort of lower limit on their weakness. Surely not in a matter quantized universe. These fields (or forces) fall off as roughly 1/(r^2) = 1/(r*r) specifically because the fields are inherently quantized. There are fewer discrete entities as we go further away from the source but we always have either all of a discrete entity or no discrete entity in the field.
Newton included the important source terms for gravity but he didn’t realize that there were weak absorption/sink terms for gravity, which explicitly cause the gravitational force. By consideration of his “rays of gravity” he may have understood that deep down the forces of gravity were actually discrete. Still, he wisely used practical continuous models (to allow relatively speedy calculations) to describe the primary interactions but he neglected to include weak absorption which slightly weakens the gravitational fields, as they interact with matter.
In his pondering of how perpetual motion devices could be produced, Newton didn’t understand the two-part nature of the graviton, which is how he missed that important Bessler principle reason of how gravity could be used to produce perpetual motion.
To obtain better correspondence between theory and experiments in many subject areas, I think that many people will need to run improved simulations using my discrete theory of everything, which theory I provide within Appendix A of my book. Alden E. Park – 23 May 2019
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“The discovery of truth is prevented more effectively, not by false appearance things present and which mislead into error, not directly by weakness of reasoning powers, but by preconceived opinion, by prejudice.”
Arthur Schopenhauer
Anyone interested in solving the riddle I posted on Schwitzgebel’s blog about the chain?
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I suspect it involves using the chain in some way other than connecting the two cars together?
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Regarding Lee Roetcisoender’s pull-or-push riddle comment for towing a car at http://schwitzsplinters.blogspot.com/2019/05/intuition-disagreement-and-rope-around.html, I first thought, if one looped a long enough chain around the back of the towed car, then one would be pushing from the back. I don’t think that is the solution. Then I more closely considered a normal chain “attached” to some point on the car. Though the towing car is normally thought to pull on the chain, since pulling can break weak links, we could ignore what is going on within individual links. We could consider both ends where the chain is “connected” and all “ahead” chain links in contact with its next “behind” link or contact point on the car. There could be considered a pushing of the “ahead” link contact point on the “behind” link contact point, since regarding where the contact points reside there is an actual change in ordering “ahead” and “behind”. The “ahead” link’s contact-point is actually behind the next “behind” link’s contact-point so there is a pushing there. One just needs to change one’s perspective on the situation. Is that close enough to count as a solution to the riddle?
We might want to be aware of such possible perspectives (pulling or pushing) or just keep an open mind, when we consider a discrete finest fundamental charge absorbing a discrete electric field, for attractive and repulsive cases. I consider that the two discrete impulses imparted by the two-part graviton (as it is absorbed) are pulls in the down direction (the direction which the attractive graviton is coming from) but as the absorption process is more carefully considered we may want to revisit the idea of push versus pull. Alden E. Park – 24 May 2019
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When we think about expansion of the universe, we think about the speed.
There could be nothing more wrong.
The expansion of the universe doesn’t have a “speed”.
The expansion of the universe is quantified by the Hubble constant, which is typically quoted in crazy units of kilometers per second per megaparsec. sc
(67…75 km/s/megaparsec … maybe 44…99).
More vividly, we can say that the closest clusters of galaxies are moving away from us at speed e.g. 0.1 c. But we see galaxies that are moving away from us over 8 c. Just 0.1c + 0.1c + … = 8c.
Only that galaxies located in area close to the edges of the universe, where the boundaries of this area (that is, the theoretical boundaries of the universe), moves with enormous speeds, (e.g. 22c), galaxies themselves expand only at a speed of 0.1 c.
Note. The problem doesn’t concern the boundaries of the universe, because the universe as an object originated independent of everything, has no boundaries.
Only that this is not the whole truth.
Moving of the boundaries of the area of the universe, when it grows, is a natural process.
So also when our enormous cluster of galaxies, pushed by 999 other large clusters of galaxies, which results in exceeding the speed of light, e.g. 11 c. Is also a natural process.
It seems all without any sense.
The most important is that the theory of the expansion of the universe has a deep sense.
Although it is difficult to prove this because of the lack of direct evidence, so only remains 99.9% certainty.
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All speed is, of course, relative. From our galaxy, another galaxy 100 megaparsecs distant is moving away from us at around 7000 km/s, but for someone in that galaxy, it’s sitting more or less still. From their perspective, it’s our galaxy that’s moving away at 7000 km/s.
The problem with saying that the other galaxy isn’t really moving, is that we have no ability to observe space itself, just what’s in it. Given that everything we see is moving away from us at speeds proportional to their distance, it makes sense to say that what we’re seeing comes from the expansion of the intervening space. We can say that the galaxies are stationary relative to space in their local region, but we can’t actually observe space itself to verify that.
So the expansion is a theory, although one pretty heavily attested. The alternative it so ss ourselves as being at the center of some great explosion, which seems extremely unlikely.
Still, like any scientific theory, the expansion one is subject to revision on new observations.
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