The controversy over the universe's expansion rate continues with a new, faster estimate.
- A new estimate of the expansion rate of the universe puts it at 73.3 km/sec/Mpc.
- This is faster than the previous estimate of expansion in the early universe.
- The discrepancy may mean fundamental theories need rethinking.
How fast is our universe is expanding? Scientists zeroed in on a new estimate of the local expansion rate and found that it doesn't square up with previously-predicted rates of expansion in the early universe, right after the Big Bang 13.8 billion years ago.
This is significant because the expansion rate is fundamental to figuring out the universe's evolution as well as the mysterious dark energy, which is believed to make up about 68 percent of the universe and impacts how fast it's growing.
Scientists made a new estimate using the surface brightness fluctuation (SBF) technique for measuring cosmic distances. They hoped this approach could achieve more precision. The method used average stellar brightness of 63 giant elliptical galaxies to come up with the calculated rate of 73.3 kilometers per second per megaparsec (km/sec/Mpc) for the universe's expansion. That implies that every megaparsec (or 3.3 million light years from Earth), the universe expands an additional 73.3 kilometers per second.
The paper's co-author, cosmologist and University of California, Berkeley professor Chung-Pei Ma, stated that this method holds much promise.
"For measuring distances to galaxies out to 100 megaparsecs, this is a fantastic method," said Ma, "This is the first paper that assembles a large, homogeneous set of data, on 63 galaxies, for the goal of studying H-naught [Hubble constant] using the SBF method."
Ma also leads the MASSIVE survey of local galaxies, which provided data for 43 of the galaxies in this analysis.
What's controversial is that if you calculate this rate using measurements of fluctuations in the cosmic microwave background or density variation data for normal matter in the early universe, you'd get a different result of 67.4 km/sec/Mpc.
The science of expansion: Andromeda, gravity, and the ‘Big Rip’
How is the difference in estimates possible, and what do the nonmatching answers suggest? The central difficulty lies in establishing certainty for the locations and relative distances of objects in space. Astronomers believe the discrepancies in calculations may point to the fact that current cosmological theories are either not fully realized or even dead wrong.
The paper's first author, John Blakeslee, an astronomer with the National Science Foundation's NOIRLab, thinks the implications of this type of research are enormous.
"The whole story of astronomy is, in a sense, the effort to understand the absolute scale of the universe, which then tells us about the physics," Blakeslee stated in a press release, "The SBF method is more broadly applicable to the general population of evolved galaxies in the local universe, and certainly if we get enough galaxies with the James Webb Space Telescope, this method has the potential to give the best local measurement of the Hubble constant."
The ultra-powerful James Webb Telescope is on track to be launched in October 2021.
"The James Webb telescope has the potential to really decrease the error bars for SBF," Ma agreed.
Other authors of the study included Jenny Greene of Princeton University, leader of the MASSIVE team, Peter Milne of the University of Arizona in Tucson, and Joseph Jensen of Utah Valley University.
Check out their new paper published in The Astrophysical Journal.
Identifying primordial ripples would be key to understanding the conditions of the early universe.
In the moments immediately following the Big Bang, the very first gravitational waves rang out.
The product of quantum fluctuations in the new soup of primordial matter, these earliest ripples through the fabric of space-time were quickly amplified by inflationary processes that drove the universe to explosively expand.
Primordial gravitational waves, produced nearly 13.8 billion years ago, still echo through the universe today. But they are drowned out by the crackle of gravitational waves produced by more recent events, such as colliding black holes and neutron stars.
Now a team led by an MIT graduate student has developed a method to tease out the very faint signals of primordial ripples from gravitational-wave data. Their results were published in December 2020 in Physical Review Letters.
Gravitational waves are being detected on an almost daily basis by LIGO and other gravitational-wave detectors, but primordial gravitational signals are several orders of magnitude fainter than what these detectors can register. It's expected that the next generation of detectors will be sensitive enough to pick up these earliest ripples.
In the next decade, as more sensitive instruments come online, the new method could be applied to dig up hidden signals of the universe's first gravitational waves. The pattern and properties of these primordial waves could then reveal clues about the early universe, such as the conditions that drove inflation.
"If the strength of the primordial signal is within the range of what next-generation detectors can detect, which it might be, then it would be a matter of more or less just turning the crank on the data, using this method we've developed," says Sylvia Biscoveanu, a graduate student in MIT's Kavli Institute for Astrophysics and Space Research. "These primordial gravitational waves can then tell us about processes in the early universe that are otherwise impossible to probe."
Biscoveanu's co-authors are Colm Talbot of Caltech, and Eric Thrane and Rory Smith of Monash University.
A concert hum
The hunt for primordial gravitational waves has concentrated mainly on the cosmic microwave background, or CMB, which is thought to be radiation that is leftover from the Big Bang. Today this radiation permeates the universe as energy that is most visible in the microwave band of the electromagnetic spectrum. Scientists believe that when primordial gravitational waves rippled out, they left an imprint on the CMB, in the form of B-modes, a type of subtle polarization pattern.
Physicists have looked for signs of B-modes, most famously with the BICEP Array, a series of experiments including BICEP2, which in 2014 scientists believed had detected B-modes. The signal turned out to be due to galactic dust, however.
As scientists continue to look for primordial gravitational waves in the CMB, others are hunting the ripples directly in gravitational-wave data. The general idea has been to try and subtract away the "astrophysical foreground" — any gravitational-wave signal that arises from an astrophysical source, such as colliding black holes, neutron stars, and exploding supernovae. Only after subtracting this astrophysical foreground can physicists get an estimate of the quieter, nonastrophysical signals that may contain primordial waves.
The problem with these methods, Biscoveanu says, is that the astrophysical foreground contains weaker signals, for instance from farther-off mergers, that are too faint to discern and difficult to estimate in the final subtraction.
"The analogy I like to make is, if you're at a rock concert, the primordial background is like the hum of the lights on stage, and the astrophysical foreground is like all the conversations of all the people around you," Biscoveanu explains. "You can subtract out the individual conversations up to a certain distance, but then the ones that are really far away or really faint are still happening, but you can't distinguish them. When you go to measure how loud the stagelights are humming, you'll get this contamination from these extra conversations that you can't get rid of because you can't actually tease them out."
A primordial injection
For their new approach, the researchers relied on a model to describe the more obvious "conversations" of the astrophysical foreground. The model predicts the pattern of gravitational wave signals that would be produced by the merging of astrophysical objects of different masses and spins. The team used this model to create simulated data of gravitational wave patterns, of both strong and weak astrophysical sources such as merging black holes.
The team then tried to characterize every astrophysical signal lurking in these simulated data, for instance to identify the masses and spins of binary black holes. As is, these parameters are easier to identify for louder signals, and only weakly constrained for the softest signals. While previous methods only use a "best guess" for the parameters of each signal in order to subtract it out of the data, the new method accounts for the uncertainty in each pattern characterization, and is thus able to discern the presence of the weakest signals, even if they are not well-characterized. Biscoveanu says this ability to quantify uncertainty helps the researchers to avoid any bias in their measurement of the primordial background.
Once they identified such distinct, nonrandom patterns in gravitational-wave data, they were left with more random primordial gravitational-wave signals and instrumental noise specific to each detector.
Primordial gravitational waves are believed to permeate the universe as a diffuse, persistent hum, which the researchers hypothesized should look the same, and thus be correlated, in any two detectors.
In contrast, the rest of the random noise received in a detector should be specific to that detector, and uncorrelated with other detectors. For instance, noise generated from nearby traffic should be different depending on the location of a given detector. By comparing the data in two detectors after accounting for the model-dependent astrophysical sources, the parameters of the primordial background could be teased out.
The researchers tested the new method by first simulating 400 seconds of gravitational-wave data, which they scattered with wave patterns representing astrophysical sources such as merging black holes. They also injected a signal throughout the data, similar to the persistent hum of a primordial gravitational wave.
They then split this data into four-second segments and applied their method to each segment, to see if they could accurately identify any black hole mergers as well as the pattern of the wave that they injected. After analyzing each segment of data over many simulation runs, and under varying initial conditions, they were successful in extracting the buried, primordial background.
"We were able to fit both the foreground and the background at the same time, so the background signal we get isn't contaminated by the residual foreground," Biscoveanu says.
She hopes that once more sensitive, next-generation detectors come online, the new method can be used to cross-correlate and analyze data from two different detectors, to sift out the primordial signal. Then, scientists may have a useful thread they can trace back to the conditions of the early universe.
Baby universes led to black holes and dark matter, proposes a new study.
- Researchers recently used a huge telescope in Hawaii to study primordial black holes.
- These black holes might have formed in the early days from baby universes and may be responsible for dark matter.
- The study also raises the possibility that our own universe may look like a black hole to outside observers.
A new paper takes a deep dive into primordial black holes that were formed as a part of the early universe when there were still no stars or galaxies. Such black holes could account for strange cosmic possibilities, including baby universes and major features of the current state of the cosmos like dark matter.
To study the exotic primordial black holes (PBHs), physicists employed the Hyper Suprime-Cam (HSC) of the huge 8.2m Subaru Telescope operating near the 4,200 meter summit of Mt. Mauna Kea in Hawaii. This enormous digital camera can produce images of the entire Andromeda galaxy every few minutes, helping scientists observe one hundred million stars in one go.
In their study, the scientists considered a number of scenarios, especially linked to the period of inflation. That is the time of quick expansion following the Big Bang, when the universe we know today came into existence with all its structures.
The researchers calculated that in the process of inflation, the climate was ripe for creating primordial black holes of various masses. And some of them reflect the characteristics predicted for dark matter.
Another way PBHs could have been created during inflation is from "baby universes" – small universes that branched off from the main one.
Hyper Suprime-Cam (HSC) is a gigantic digital camera on the Subaru Telescope
Credit: HSC project / NAOJ
A baby or "daughter" universe would ultimately collapse but the tremendous release of energy would lead to the formation of a black hole, explains the press release from the Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU) in Japan, one of the institutions participating in this study.
What's also fascinating, some of the bigger baby universes might not have gone so quietly. Above a certain critical size, the theory of gravity developed by Albert Einstein permits that such a universe may be perceived differently by observers. If you were inside it, you'd see an expanding universe, while if you were outside, this baby universe would look like a black hole. A conjecture that leads to wondering – are we potentially on the inside or outside of such a universe ourselves?
If you follow this multiverse logic, it also may be possible that while primordial black holes would appear to us as black holes, their true structural natures could be concealed by their "event horizons" – the boundaries surrounding black holes from which not even light can escape.
It should be noted, while strange or counter-intuitive, this is not the first go-around for these types of ideas. A study earlier in 2020 found that so-called "charged" black holes may include within them endlessly-repeating fractal universes of various sizes, including miniature, that can be stretched and deformed in all directions.
To solidify their theories and to find a primordial black hole, the researchers will continue using the Subaru Telescope, with some promising PBH candidates already emerging.
The international team of particle physicists working on the research came from the University of California, Los Angeles and the Kavli Institute. The group included cosmologists and astronomers Alexander Kusenko, Misao Sasaki, Sunao Sugiyama, Masahiro Takada and Volodymyr Takhistov.
Check out their new paper "Exploring Primordial Black Holes from the Multiverse with Optical Telescopes" in Physical Review Letters.
The expansion of the universe is speeding up—contrary to what many physicists expected. A "heat death" is coming, but it's not what you think.
- The expansion of the universe is accelerating as the force of dark energy wins out over the pull of all the universe's collective gravity.
- As every object in space moves farther and farther away from all other objects in space, the universe will reach a state of maximum entropy, and 'heat death' will ensue. As astrophysicist Dr. Katie Mack points out, heat death is not actually a hot phenomenon—it's also known as the "Big Freeze."
- Around 100 billion years from now, the universe will have expanded so much that distant galaxies won't be visible from Earth, even with high-powered telescopes. Stars will disappear in a trillion years and new stars will no longer form. The "good" news is that humans probably won't be around to witness the machine as it breaks down and dies.
Sir Roger Penrose claims our universe has been through multiple Big Bangs, with more coming.
- Roger Penrose, the 2020 Nobel Prize winner in physics, claims the universe goes through cycles of death and rebirth.
- According to the scientist, there have been multiple Big Bangs, with more on the way.
- Penrose claims that black holes hold clues to the existence of previous universes.
Sir Roger Penrose, a mathematician and physicist from the University of Oxford who has just shared this year's Nobel Prize in physics, claims our universe has gone through multiple Big Bangs, with another one coming in our future.
Penrose received the Nobel for his working out mathematical methods that proved and expanded Albert Einstein's general theory of relativity, and for his discoveries on black holes, which showed how objects that become too dense undergo gravitational collapse into singularities – points of infinite mass.
As he accepted the Prize, Penrose reiterated his belief in what he called "a crazy theory of mine" that the universe will expand until all matter will ultimately decay. And then a new Big Bang will bring a new universe into existence.
"The Big Bang was not the beginning," Penrose said in an interview with The Telegraph. "There was something before the Big Bang and that something is what we will have in our future."
What proof does the physicist have for this theory he dubbed "conformal cyclic cosmology" (CCC) that goes against the current Big Bang dogma? He said he discovered six "warm" sky points (called "Hawking Points") which are all about eight times larger than the diameter of the Moon. The late Professor Stephen Hawking, whose name they bear, proposed that black holes "leak" radiation and would eventually evaporate. As this might take longer than the age of the universe we are currently inhabiting (13.77 billion years old), spotting such holes is very unlikely.
Penrose (89), who collaborated with Hawking, thinks that we are, in fact, able to observe "dead" black holes left by previous universes or "aeons". If proven correct, this would also validate Hawking's theories.
The physicist's 2020 paper, published in the Monthly Notices of the Royal Astronomical Society, offers evidence of "anomalous circular spots" in the cosmic microwave background (CMB) that have raised temperatures. The data revealing the spots came from Planck 70 GHz satellite and was confirmed by up to 10,000 simulations.
Hot spots in Planck CMB data.
Credit: ESA and the Planck Collaboration
Penrose's 2018 paper pinpointed radiation hot spots in the CMB as possibly being produced by evaporating black holes. A 2010 paper by Penrose and Vahe Gurzadyan from the Yerevan Physics Institute in Armenia found support for cyclic cosmology in the uniform temperature rings within the CMB. The scientists proposed then that the rings were caused by signatures of gravitational waves from colliding black holes in a universe that preceded ours.
These ideas are controversial within the cosmologist community, with some pointing to the difficulty of conforming an infinitely big universe in one aeon to a super-small one in the next. This would necessitate making all particles lose mass as the universe gets old.
For another fascinating Penrose theory, check out his views on the quantum-level origins of our consciousness.