New JWST Data Explores 'Hubble Constant' Tension for Universe's Expansion Rate (space.com) 31
"Scientists can't agree on the exact rate of expansion of the universe, dictated by the Hubble constant," a new article at Space.com reminds us:
The rate can be measured starting from the local (and therefore recent) universe, then going farther back in time — or, it can be calculated starting from the distant (and therefore early) universe, then working your way up. The issue is both methods deliver values that don't agree with each other. This is where the James Web Space Telescope (JWST) comes in. Gravitationally lensed supernovas in the early cosmos the JWST is observing could provide a third way of measuring the rate, potentially helping resolve this "Hubble trouble." "The supernova was named 'supernova Hope' since it gives astronomers hope to better understand the universe's changing expansion rate," Brenda Frye, study team leader and a University of Arizona researcher, said in a NASA statement.
This investigation of supernova Hope began when Frye and her global team of scientists found three curious points of light in a JWST image of a distant, densely packed cluster of galaxies. Those points of light in the image were not visible when the Hubble Space Telescope imaged the same cluster, known as PLCK G165.7+67.0 or, more simply, G165, back in 2015. "It all started with one question by the team: 'What are those three dots that weren't there before? Could that be a supernova?'" Frye said.
The team noted a "high rate of star formation... more than 300 solar masses per year," according to NASA's statement: Dr. Frye: "Initial analyses confirmed that these dots corresponded to an exploding star, one with rare qualities. First, it's a Type Ia supernova, an explosion of a white dwarf star. This type of supernova is generally called a 'standard candle,' meaning that the supernova had a known intrinsic brightness. Second, it is gravitationally lensed. Gravitational lensing is important to this experiment. The lens, consisting of a cluster of galaxies that is situated between the supernova and us, bends the supernova's light into multiple images...
To achieve three images, the light traveled along three different paths. Since each path had a different length, and light traveled at the same speed, the supernova was imaged in this Webb observation at three different times during its explosion... Trifold supernova images are special: The time delays, supernova distance, and gravitational lensing properties yield a value for the Hubble constant... The team reports the value for the Hubble constant as 75.4 kilometers per second per megaparsec, plus 8.1 or minus 5.5... This is only the second measurement of the Hubble constant by this method, and the first time using a standard candle.
Their result? "The Hubble constant value matches other measurements in the local universe, and is somewhat in tension with values obtained when the universe was young."
This investigation of supernova Hope began when Frye and her global team of scientists found three curious points of light in a JWST image of a distant, densely packed cluster of galaxies. Those points of light in the image were not visible when the Hubble Space Telescope imaged the same cluster, known as PLCK G165.7+67.0 or, more simply, G165, back in 2015. "It all started with one question by the team: 'What are those three dots that weren't there before? Could that be a supernova?'" Frye said.
The team noted a "high rate of star formation... more than 300 solar masses per year," according to NASA's statement: Dr. Frye: "Initial analyses confirmed that these dots corresponded to an exploding star, one with rare qualities. First, it's a Type Ia supernova, an explosion of a white dwarf star. This type of supernova is generally called a 'standard candle,' meaning that the supernova had a known intrinsic brightness. Second, it is gravitationally lensed. Gravitational lensing is important to this experiment. The lens, consisting of a cluster of galaxies that is situated between the supernova and us, bends the supernova's light into multiple images...
To achieve three images, the light traveled along three different paths. Since each path had a different length, and light traveled at the same speed, the supernova was imaged in this Webb observation at three different times during its explosion... Trifold supernova images are special: The time delays, supernova distance, and gravitational lensing properties yield a value for the Hubble constant... The team reports the value for the Hubble constant as 75.4 kilometers per second per megaparsec, plus 8.1 or minus 5.5... This is only the second measurement of the Hubble constant by this method, and the first time using a standard candle.
Their result? "The Hubble constant value matches other measurements in the local universe, and is somewhat in tension with values obtained when the universe was young."
Re:Those error bars are huge. (Score:5, Informative)
The premise of which is childish to say the least. The idea that all the money spent on JWST would just be laying around to be used for a natural disaster nearly thirty years in the future.
How weak.
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While he's at it, he could also ask for a cessation in money spent on, say, TV shows. Or dog competitions. Sports events. Concerts. Or any activity that doesn't focus strictly on the most basic human needs. /s
Re: Those error bars are huge. (Score:1)
What if the universe is expanding at different rates all over?
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That has to be true. It has to be true because things that are heavy and close (say galaxies) attract each other, so even if they aren't bound they will slow their separation. Whereas in the voids there's no such attraction happening.
OTOH, I'm not at all sure this can explain the "tension".
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we have people drowning and starving in North Carolina.
Republicans in the House voted against money for FEMA [newsweek.com] just days before Helene hit. This is part of their Project 2025 agenda to remove FEMA altogether. So if you're whining now that FEMA doesn't have enough money to help those folks in North Carolina, just imagine what will happen when FEMA doesn't exist if the convicted felon gets into office.
Also, that couch humper from the Senate didn't even bother to show up [newsweek.com] tor the vote which would have funded F
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Re: hubble did not believe universe is expanding. (Score:4, Interesting)
Religious beliefs (Score:1)
and neither do I.
Something that extends forever in every direction cannot expand. It just is. always has been. always will be.
We have no evidence that the universe extends forever.
Just because something has no edge doesn't mean it goes on forever. An ant walking on a balloon can only see a small portion of the balloon up to the local horizon, it won't have an edge, yet it doesn't go forever. And the balloon can be expanding, giving the ant the impression that everything else on the surface is moving away from him.
Lots of times these high-end scientific concepts require a bit of belief. The evidence is for one side or the other is
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Well, the best evidence is that we can't be affected by anything outside of our light cone. It also seems to be true that within our light cone there is no wrap-around. So effectively the universe is infinite.
I'm not sure that argument convinces me, but it's plausible.
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More accurately, the universe could be unbounded. The short way to think of it is to look at Escher's drawings of circle tilings that get increasingly smaller as they near the "edge". The "edge" is not really part of the drawing. In topology, think of the line segment 0 and 1 and use the real numbers as a coordinate system, the real numbers, to indicate the set of those points The key is the numbers are between those end points, the end points are not in the set. One can get as close as one likes to 1, but
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It could be unbounded like an Escher drawing, but I don't believe that there is any good evidence that that's what happens at the edge of the light cone. (In fact, I think it would take lots of special pleading and violation of the Copernican principle for it to be true. Two observers at different locations will have different edges of their light cones. Escher's unboundedness depends on a special point of observation.)
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> we can't be affected by anything outside of our light cone.
Has that actually been proven or just assumed?
Re: Religious beliefs (Score:1)
What about entanglement of particles, one of which has long since traveled beyond the cone's boundaries?
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I don't think it's been proven. I'm not sure how it could be proven. I'm not even sure how it could be disproven. But if it's wrong, then relativity is wrong.
(Of course we *know* that either relativity or quantum theory is wrong, but we've never been able to find a place where either one fails.)
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Lots of times these high-end scientific concepts require a bit of belief. The evidence is for one side or the other is weak, ambiguous, or even non-existent.
You are right. We are guessing as to the meaning of things beyond our immediate reach. That is the nature of investigation - propose hypotheses and theories that seem plausible to one degree or another, then measure, test, analyze, refine until the real "truth" starts to come into focus. Modern astrophysics and cosmology has more open theories and question that answers, and many current theories are likely to fade away as we learn more, but they serve as a basis for starting to understand.
But, you are wr
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Light waves, like all waves, transmit in a medium and lose energy as they travel.
I knew that there are still some flat-Earthers and even some people who are still hanging on to geocentrism, but I didn't think there was anyone left who still believed in aether.
Constant (Score:2)
Re:Constant (Score:4, Informative)
Constant in space, not time. Even the most simple cosmological models currently considered don't think we live in a de Sitter universe.
The Friedmann equation is Hubble^2 = (constants) * energy density + Possible spatial curvature/a^2
Where Hubble = 1/a da/dt and a is the scale factor or "size" of the universe (or representative cell therein).
And if it's not constant in space (or has different rates of expansion in different directions) then we have to rethink the cosmological principles (homogeneity and isotropy on large scales).
As the universe expands, the energy density reduces, so the Hubble parameter goes down. Eventually at the universe becomes void of matter it will tend to a constant set by the cosmological constant (we think). But it has changed very much over the history of the universe.
The tension here is that if we take the current observed value and track it back to early times, the observed value doesn't quite match up with the values we'd get if we just took the earliest observations. There's a lot of possible reasons for this, but don't think that we haven't considered "it's not a constant" - we have. Extensively.
Another way to view it (Score:2)
Constant in space, not time. Even the most simple cosmological models currently considered don't think we live in a de Sitter universe.
The Friedmann equation is Hubble^2 = (constants) * energy density + Possible spatial curvature/a^2
Where Hubble = 1/a da/dt and a is the scale factor or "size" of the universe (or representative cell therein).
And if it's not constant in space (or has different rates of expansion in different directions) then we have to rethink the cosmological principles (homogeneity and isotropy on large scales).
As the universe expands, the energy density reduces, so the Hubble parameter goes down. Eventually at the universe becomes void of matter it will tend to a constant set by the cosmological constant (we think). But it has changed very much over the history of the universe.
The tension here is that if we take the current observed value and track it back to early times, the observed value doesn't quite match up with the values we'd get if we just took the earliest observations. There's a lot of possible reasons for this, but don't think that we haven't considered "it's not a constant" - we have. Extensively.
Another way to view it is to think in terms of construction.
Assume the universe is computable, that means it can be simulated using a computer program.
The program has to represent space in some way, and regardless of the implementation (or compression algorithm) space can be considered a large 3D array of points, possible positions in the universe.
If expansion is homogenous, then all of space is expanding all the time. Everywhere you look you see everything expanding away from you, like the surface of an ex
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That's also a pretty simple, perhaps the simplest explanation. The rate of expansion is a secondary effect from the rate of generating new locations in space, the generation rate is fixed and unchanging, but as a result the visible expansion seems to be slowing down.
You put much effort into this long post. Unfortunately your thinking process goes wrong from this very first assumption of yours. The current evidence from standard candles points to the fact that the rate of expansion is speeding up, not slowing down.
And your model? (Score:2)
That's also a pretty simple, perhaps the simplest explanation. The rate of expansion is a secondary effect from the rate of generating new locations in space, the generation rate is fixed and unchanging, but as a result the visible expansion seems to be slowing down.
You put much effort into this long post. Unfortunately your thinking process goes wrong from this very first assumption of yours. The current evidence from standard candles points to the fact that the rate of expansion is speeding up, not slowing down.
My very first assumption was indeed wrong, the universe is not computable, but I did that on purpose to make for a simpler post because that point is irrelevant. Not being computable can arise from several factors, and these factors can be dealt with in the overall model to make testable predictions.
That the Hubble constant is increasing is not in any way a fact pointed to by the evidence; in fact the evidence [cloudfront.net] is right now uncertain; or perhaps conditioned on the year of publication. The Hubble constant tak
Re: Another way to view it (Score:2)
Re: Constant (Score:1)
ãSdon't think that we haven't considered "it's not a constant" - we have. Extensively.ã
How much hubris is involved in keeping cherished assumptions such as homogeneity and isotropy on large scales?
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We know it's not constant in space because gravity prevents that. The local group is gravitationally bound, and is not expanding. Get beyond that and in at least some directions you see expansion.
OTOH, this probably isn't a large enough effect to explain the tension. (I'm no expert in the field, and not even extremely interested, so correct me if I'm wrong.)
IIUC, the Hubble "constant" is intended to be an average rate of expansion. It's always seemed to me that for it to be constant over time would requ
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1) We already know it isn't necessary under the current model for it to be constant. The Inflationary Epoch is worth reading up on.
2) The issue isn't that it might be variable, the issue is we have two presumed reliable methods for measuring it, and we're getting two different answers whose margins of error do not overlap.