Speed of universe’s expansion remains elusive
Discrepancy between measures of Hubble constant suggests influence of some astronomical unknown
In August of 2011, researchers discovered SN 2011fe, a type 1a supernova 21 million light-years away in galaxy M101
(images show the galaxy before and after the supernova, with the supernova circled at right).
Studies using type 1a supernovas as “standard candles” to measure how fast the universe expands
(the Hubble constant) produce a result in conflict with other data used to infer the cosmic growth rate.
NASA, Swift, Peter Brown, Univ. of Utah
Unless you are a recent arrival from another universe, you’ve no doubt heard that this one is expanding. It’s getting bigger all the time. What’s more, its growth rate is accelerating. Every day, the universe expands a little bit faster than it did the day before.
Those day-to-day differences are negligible, though, for astronomers trying to measure the universe’s expansion rate. They want to know how fast it is expanding “today,” meaning the current epoch of cosmic history. That rate is important for understanding how the universe works, knowing what its ultimate fate will be and even what it is made of. After all, the prime mission of the Hubble Space Telescope when it was launched in 1990 was to help determine that expansion rate (known, not coincidentally, as the Hubble constant, named for the astronomer Edwin Hubble).
Since then evidence from Hubble (the telescope) and other research projects has established a reasonably precise answer for the Hubble constant: 73, in the units commonly used for this purpose. (It means that two independent astronomical bodies separated by 3.26 million light-years will appear to be moving away from each other at 73 kilometers per second.) Sure, there’s a margin of error, but not much. The latest analysis from one team, led by Nobel laureate Adam Riess, puts the Hubble constant in the range of 72–75, as reported in a paper posted online January 3. Considering that as late as the 1980s astronomers argued about whether the Hubble constant was closer to 40 or 90, that’s quite an improvement in precision.
But there’s a snag in this success. Current knowledge of the universe suggests a way to predict what the Hubble constant ought to be. And that prediction gives a probable range of only 66–68. The two methods don’t match.
“This is very surprising, I think, and very interesting,” Riess, of the Space Telescope Science Institute in Baltimore, said in a talk January 9 at a meeting of the American Astronomical Society.
It’s surprising because astrophysicists and cosmologists thought they had pretty much figured the universe out. It’s made up of a little bit of ordinary matter, a lot of some exotic “dark matter” of unknown identity, and even more of a mysterious energy permeating the vacuum of space, exerting gravitational repulsion. Remember that acceleration of the expansion rate? It implies the existence of such energy. Because nobody knows what it is, people call it “dark energy,” while suspecting that its real name is lambda, the Greek letter that stands for “cosmological constant.” (It’s called a constant because any part of space should possess the same amount of vacuum energy.) Dark energy contributes something like 70 percent of the total mass-energy content of the universe, various lines of evidence indicate.
If all that’s right, then it’s not all that hard to infer how fast the universe should be expanding today. You just take the recipe of matter, dark matter and dark energy and add some ghostly subatomic particles known as neutrinos. Then you carefully measure the temperature of deep space, where the only heat is the faint glow remaining from the Big Bang. That glow, the cosmic microwave background radiation, varies slightly in temperature from point to point. From the size of those variations, you can calculate how far the radiation from the Big Bang has been traveling to reach our telescopes. Combine that with the universe’s mass-energy recipe, and you can calculate how fast the universe is expanding. (You can, in fact, do this calculation at home with the proper mathematical utensils.)
An international team’s project using cosmic microwave background data inferred a Hubble constant of 67, substantially less than the 73 or 74 based on actually measuring the expansion (by analyzing how the light from distant supernova explosions has dimmed over time).
When this discrepancy first showed up a few years ago, many experts believed it was just a mirage that would fade with more precise measurement. But it hasn’t.
“This starts to get pretty serious,” Riess said at the astronomy meeting. “In both cases these are very mature measurements. This is not the first time around for either of these projects.”
One commonly proposed explanation contends that the supernova studies are measuring the local value of the Hubble constant. Perhaps we live in a bubble, with much less matter than average, skewing expansion measurements. In that case, the cosmic microwave background data might provide a better picture of the “global” expansion rate for the whole universe. But supernovas observed by the Hubble telescope extend far enough out to refute that possibility, Riess said.
“Even if you thought we lived in a void, you still are basically stuck with the same problem.”
Consequently it seems most likely that something is wrong with the matter-energy recipe for the universe (technically, the cosmological standard model) used in making the expansion rate prediction. Maybe the vacuum energy driving cosmic acceleration is not a cosmological constant after all, but some other sort of field filling space. Such a field could vary in strength over time and throw off the calculations based on a constant vacuum energy. But Riess pointed out that the evidence is growing stronger and stronger that the vacuum energy is just the cosmological constant. “I would say there we have less and less wiggle room.”
Another possibility, appealing to many theorists, is the existence of a new particle, perhaps a fourth neutrino or some other relativistic (moving very rapidly) particle zipping around in the early universe.
“Relativistic particles — theorists have no trouble inventing new ones, ones that don’t violate anything else,” Riess said. “Many of them are quite giddy about the prospect of some evidence for that. So that would not be a long reach.”
Other assumptions built into the current cosmological standard model might also need to be revised. Dark matter, for example, is presumed to be very aloof from other forms of matter and energy. But if it interacted with radiation in the early universe, it could have an effect similar to that of relativistic particles, changing how the energy in the early universe is divided up among its components. Such a change in energy balance would alter how much the universe expands at early times, corrupting the calibrations needed to infer the current expansion rate.
It’s not the first time that determining the Hubble constant has provoked controversy. Edwin Hubble himself initially (in the 1930s) vastly overestimated the expansion rate. Using his rate, calculations indicated that the universe was much younger than the Earth, an obvious contradiction. Even by the 1990s, some Hubble constant estimates suggested an age for the universe of under 10 billion years, whereas many stars appeared to be several billion years older than that.
Hubble’s original error could be traced to lack of astronomical knowledge. His early overestimates turned out to be signals of a previously unknown distinction between different generations of stars, some younger and some older, Riess pointed out. That threw off distance estimates to some stars that Hubble used to estimate the expansion rate. Similarly, in the 1990s the expansion rate implied too young a universe because dark energy was not then known to exist and therefore was not taken into account when calculating the universe’s age.
So the current discrepancy, Riess suggested, might also be a signal of some astronomical unknown, whether a new particle, new interactions of matter and radiation, or a phenomenon even more surprising — something that would really astound a visitor from another universe.
=============================
There may be links in the Original Article that have not been reproduced here.
Tags
Who is online
418 visitors
I love this stuff.....
This is all relatively new stuff so I think we are in for quite a few surprises in the future. Cosmology and particle physics (the extremes) remain replete with mystery.
String theory! Miammmmm........
Theoretical physics will definitely remain wild - it could be called genuine science fiction. It is sophisticated, informed speculation sans any means to falsify. But one of these days we might see something like string theory gain empirical legs and actually become a bona fide theory.
Please elaborate. Sorry, I am drawing a blank. Is string theory something along the line of multi-verse?
Yes string theory is theoretical science (vs. empirical science). It is, in effect, pure mathematics founded on the rules of physics (which ultimately come from empirical research). The problem with string theory is that there is no way (currently) to test it - no way to determine if it is a bona fide theory of science (a predictive explanation of what we observe) or simply nonsense. Even today, it could be nonsense.
If it is not nonsense, then string theory (actually M-theory) is a contender for a theory of everything - that goal that eluded Einstein and all scientists since. The theory of everything would explain everything from particle physics to cosmology with the center of attention being gravity.
String theory is related to the concept of a multiverse in which many simultaneous distinct universes coexist. Again this may be utter nonsense. No matter how persuasive the mathematics, without empirical grounding - without a method of falsification, this is just a (very) educated guess.
Then, I follow you train of thought. Thank you. Interesting. Possible different and varying "other" forms of life and finite or infinite numbers of universes?
Possibly. But even within our own (expanding) universe the likelihood of extraterrestrial life is quite high. It is silly to think of ourselves as significant much less the center of the universe.
I agree there is no reason to believe there is extraterrestrial life. But there is a very high probability that planet Earth is not the only host of life in the universe. Do you disagree?
Ever notice that science articles are poorly attended? This is not a function of this site - seems commonplace. The articles that grab interest tend to be meta, tabloid, salacious, simplistic, etc.
I've decided not to pay attention.
I'll seed stuff I've found interesting, and I don't worry about Replies.
I also seed articles that are more than three paragraphs. That is to say, far more than most members are able to read. I've noticed the a good development of a subtle idea requires more than three sentences... Gosh!
If other members prefer to rehash the same-old-same-old, that's ok.. for them. Not me, thanks.
It is all very, very, very, interesting, Bob!
Thank you.
Bob, in addition, in 2018, I will be seeding articles of all kinds of interest to me and possibly other worldviews. If they rise or fall-flat will not be the driving motivation of my 'deliverables.' Insights will drive the day.
Now then, what is the thing of interest in this article: Something new, something known, or something that makes you go hmm?
I've always found astrophysics fascinating. I'm not sure why.
Perhaps our (mankind's) gradual appropriation of the universe -- at least in constantly improving understanding of it -- somewhat balances the vertigo of being just one person among ten billion on a teeny-tiny planet on the periphery of a galaxy that is one of trillions...
It is super important. Even when we discuss it, and we should, we can reflect on how something so invaluable, or is that chance-oriented, as ourselves should possess minds to think off-planet. Moreover, there is the simple exhilaration and thrill of conversing it all with like-minded human-beings. It can certainly be good for the soul! Count me in!
IMNAAHO, we don't yet have enough data to draw any conclusions.
To be clear, I do accept the universe is expanding.
Please, to get this discussion going in the right direction - How are the two photos above with the supernova included helping to explain universal expansion? The pictures are mostly similar.
The two photos are identical except for the little circle at the bottom on the right: a type 1a supernova. Astronomers now know the life cycles of various types of stars in great detail. They know the intrinsic brilliance of a type 1a, and therefore can calculate the distance of this one by measuring its apparent brilliance.
They do lots and lots of such calculations, all around the sky. They have shown that all distant stars are receding from us -- that the universe is expanding. Moreover, they have found that the further away a star is, the faster it is receding.
That's obviously important, because the mass of the universe can be deduced from its volume, and the density of the "stuff" that composes it.
So we need accurate estimates of how fast the universe is expanding, and how much that expansion is accelerating. And this is where there's a problem! Astronomers have two different ways of estimating that acceleration... and the two methods do not give the same result.
Something's wrong in the presumptions... and scientists love it when they run across such a problem! It means there is a "discovery" to be made. Eureka and all that... The race is on to be the hero who resolves the enigma!
So these "standard candles" are being used to determine the acceleration and in some cases the deceleration in the universe?
Yes.
Acceleration only. The universe is expanding, and that expansion is accelerating. The 1a supernovas supply the yardstick.
Astronomers have quite a few standard candles - objects with known luminosity. In this case the object is a type 1a supernova. So what they do is compare the known actual luminosity of a type 1a supernova to the measured luminosity (what we actually see). In effect it becomes a straightforward calculation to plug in the measured luminosity and calculate the distance of the object from us.
Given the means to translate measured luminosity to distance, astronomers can (over time) measure the expansion rate of the universe. This is but one of many such measurement methods.
Here I thought with all their data and calculations the answer would have been "42" instead of 73, lol.
To be clear, I agree the universe is expanding. Still, is this expansion even or uneven throughout the universe?
Excellent question!
There are many, many astronomers working to get an answer. I haven't read anything recently. At last news, we were at: "It seems to be uniform, but we want more data..."
Can we say the universe exploded or is exploding?
Yes, but only as a very approximate approximation. The events at the instant of the Big Bang remain unknown, beyond the reach of particle physics as we know it. The conditions were too radically different.
When we say "explosion" we think of a blast, with a wave front, and heterogeneous debris. That's not an appropriate image.
OTOH, it was a point of heat to a point that we cannot imagine. There wasn't any light because it was too hot for photons to exist. And lots of other strange stuff like that.
Of course, the fundamental idea - all of the mass of all the billions of galaxies compacted into a tiny volume - is kinda hard to comprehend...
Also the four fundamental forces were unified (best science can tell).
1. Gravity. 2. Electromagnetism. 3. Strong and, 4. Weak nuclear forces.
Indeed. Gravity is understood to be the first force to split off from the others; at least according to calculations. Funny how in this topic we are seeing the benefit of formal science. While it is not certain that physics -as we understand it- was in effect when we get within 10^-30 seconds from the event, if it was in effect then science can offer amazing insights into the origin of the universe such as the origin of the four fundamental forces.
Mathematics, too... or rather... In those first instants after the Big Bang, conditions were so extreme that there's no way we're ever going to duplicate them for experimentation. So math is the tool physicists use. Math is "formal science".
That's too near the moment of creation, no?
The language for formally expressing (and analyzing) properties and relationships of science - the 'knowledge' of science.
Right there on top of it. Go back 10^-30 seconds (imagine how tiny that number is) and the equations start delivering infinities.
I'd avoid the word "creation". The verb "to create" is transitive, requiring a subject... someone / something that "creates". We don't know the first instants after the Big Bang, so we don't know if there was a creator, or some other mechanism.
HA! It is how I 'speak,' Bob! I was in another part of the house, about a few minutes after writing the word - when it dawned on me somebody was going to 'trip' on that word, "creation." Forgive/accept me for my manner of discourse it is genuine, please.
probably not to one so fickle as yourself
perhaps'
u prefer fecal , that matters /?
But it does matter to quite a few people. Clearly the topic of the origin of the universe has worldwide interest. Why would you think none of this matters to anyone?
Well, as a matter of fact, that is nowhere close to what I mean.
What point, then, are you trying to make?
Does learning matter?
Too late. Let's talk some science buddy!
Do you know what science hypothesizes (currently) as the reason for accelerating expansion of the known universe?
no, where ?
asz u no, eye c all graham atticalee uncohwrecked righting awn the walll
on a tad more serious knowte
you will have more serious correspondence here, unless you choose to chat with A I imho
... and for the same reasons, these are the articles I'll be seeding. the "News & Politics" forum has become pointless, with each member endlessly repeating the same... stuff. So I'll be seeding mostly to the other forums, from science to history.
If it doesn't matter to you, then why are you bothering to disrupt it? Wouldn't it be more reasonable to let us waste our time in peace?
I understand, all the more easily because your other posts have shown your intense interest in the topic. I think all in our little circle understand, but in a different context you might want to beware...
I enjoy your input and seeds on the political forum, but can also understand your frustration.
Indeed.
And some people abuse that faculty, posting junk that is totally irrelevant to the seed, in pure vandalism.
But feel free to do so! There is nothing in the CoC to prevent members from crapping on other members' seeds/articles if that's they way they like to behave.
We have quite a few members who never, ever participate productively. They are only ever unpleasant asses. I don't understand how they derive any pleasure from this behavior, but some of them have been constant for many years, now so I hardly expect them to change.
If you are a person who finds pleasure in being annoying, in crapping on others' work while never producing anything of your own... NT is the place for you!
(Actually... I have a theory... Perhaps you could confirm it. NT'S asshole vandals know that their behavior is despicable, so they do not dare in the real world. But online, with a CoC that allows basically anything... they feel liberated to do their worst. Does that seem like a reasonable theory to you?)
Oh don't fret the small stuff. It happens somewhere on this planet every day that someone misses out on a word or several. The rest of us just have to be big enough to follow the train of thought, if possible (and I did) and continue on! (Smile.)
Speaking of the train of thought, was thinking of this expansion of the universe explanation problem, dark matter, dark energy, vacuum energy (kinda weird for if a vacuum is empty then where's the energy coming from? On earth the energy is in everything surrounding the vacuum). For acceleration to occur then something needs to be pushing or pulling with ever more energy, since all matter and energy we can account for is measurable and can't explain the acceleration then it's something we can't measure yet therefore dark matter and dark energy has to be the explanation. What if they are thinking of the universe wrong, prior to the Big Bang the super massive singularity was spinning at such a speed that the mass overcame gravity and the first expansion, gravity tends to make everything spin, planets and moons, solar systems, galaxies, so why not the universe? If its the universe that spinning then as objects expand further out the tug of gravity lessens giving the impression of acceleration. Does a fish know its in water?
It could give the impression of our universe flying apart or collapsing back in on itself, no?
What's it all mean Basil?
It means they really don't know. If our universe is the result of a super massive singularity and all the mass of that singularity makes up our universe wouldn't it also stand to reason that all energy including light wouldn't be able to escape our universe, so in essence we are still in a black hole. All the background noise in the universe could be matter being turned into energy as it enters our black hole.