The recent detection of the sky-averaged 21-cm cosmological signal indicates a stronger absorption than the maximum allowed value based on the standard model. One explanation for the required colder primordial gas is the energy transfer between the baryon and dark matter fluids due to non-gravitational scattering. Here, we explore the thermal evolution of primordial gas, collapsing to form Population III (Pop III) stars, when this energy transfer is included. Performing a series of one-zone calculations, we find that the evolution results in stars more massive than in the standard model, provided that the dark matter is described by the best-fit parameters inferred from the 21-cm observation. On the other hand, a significant part of the dark matter parameter space can be excluded by the requirement to form massive Pop III stars sufficiently early in cosmic history. Otherwise, the radiation background needed to bring about the strong Wouthuysen-Field coupling at z >~ 17, inferred to explain the 21-cm absorption feature, could not be builtup. Intriguingly, the independent constraint from the physics of first star formation at high densities points to a similarly narrow range in dark matter properties, compared to the conclusions from the 21-cm signal imprinted at low densities.
THE WOODLANDS, TEXAS—The stately solar system of today was in turmoil in its first several million years, theorists believe, with giant planets sowing chaos as they strayed far from their current orbits. But corroborating evidence has been thin—until now.
Scientists have found a new window into the early dynamics: a curious chemical divide in the dozens of species of meteorites. The picture has emerged over several years, but in work presented last week at the Lunar and Planetary Science Conference here, a group of German geochemists reported clinching evidence. They tested 32 meteorites representing nearly all known types and found that “any meteorite you take, it belongs to either one of these groups,” says Thorsten Kleine, a geochemist at the University of Münster in Germany who led the work.
Those divergent chemistries imply distinct origin stories for asteroids, the parent bodies of most meteorites. One group formed from grist that began near the current location of the asteroid belt. The others coalesced much farther out, beyond a proto-Jupiter, near where Saturn orbits today. Only later, pushed and pulled by the wandering giant planets, did these immigrant asteroids find their home in today’s asteroid belt. Bill Bottke, a planetary dynamicist at the Southwest Research Institute (SwRI) in Boulder, Colorado, thinks the chemical divide holds other clues to the timing and formation of the planets. “It really seems to be a powerful mechanism for understanding our solar system.”
Paul Warren, a meteoriticist at the University of California, Los Angeles, was the first to notice what has come to be called the Warren gap. He gathered measurements of chromium and titanium isotopes for two meteorite types. Those metals, forged by the explosions of dying stars, were mixed throughout the disk of gas and dust from which planets and asteroids took shape. Warren expected his meteorites to display a continuum of isotopic abundances, because he assumed they had formed across the one broad region of the asteroid belt. Instead, he found that, in one meteorite type, called carbonaceous chondrites, the isotope levels were starkly different from other types. “I knew a good thing when I saw it,” he says.
In a 2011 study, Warren argued that such a dichotomy could exist only if the two groups were separated for millions of years at formation. The most plausible source of that split was a void created by the gravity of a proto-Jupiter. But carbonaceous chondrites are known to have formed later than other meteorites—so it was possible that their peculiar isotopic chemistry reflected changes over time in the disk, rather than a distinct place of origin.
A few years ago, Kleine’s group began looking at isotopes of molybdenum, another metal, and found a Warren gap there, too. It also found that iron meteorites fell into two populations even though they must all have formed at about the same time. That meant a physical barrier. “And the most obvious one would be Jupiter,” Kleine says.
Kleine’s team began spelling out the implications: By 1 million years after the solar system’s start, Jupiter’s core had grown large enough to sweep up dust in its path, creating a barrier. A new influx of metalrich dust to the solar system, perhaps from a nearby supernova, would have augmented isotopes in the outer asteroids but not the inner ones. Then, 3 million to 4 million years later, Jupiter migrated inward, mixing the two reservoirs. The Warren gap is both a validation of dynamic solar system models that predict a similar scenario, and a constraint they must reckon with, says Kevin Walsh, a SwRI dynamicist.
Now, scientists are gleaning other clues about the early solar system from the meteorites. One group is studying rare meteorites that mix up carbonaceous and noncarbonaceous components, a hint that they formed just after Jupiter’s migration, in an effort to date when the two reservoirs combined. And by comparing molybdenum isotopes in rocks from Earth’s mantle with those in meteorites, Kleine’s team has found preliminary signs that Earth’s water was partially delivered by a shower of impactors from the more distant asteroid population.
The meteorite studies could even set back the clock on the age of the 4.6-billion-year-old solar system itself. That date comes from the decay of uranium in calcium-aluminum–rich inclusions in meteorites. These little metal snowflakes, created by the sun’s heat, are thought to have arisen in the earliest years of the solar system. But scientists have long wondered why carbonaceous meteorites are richer in these snowflakes. It appears that the inclusions are also isotopically similar to the outer solar system meteorites. Researchers now speculate that they formed far from the sun, driven by heat from a proto-Jupiter. If so, some inclusions must have formed after Jupiter took shape, meaning they are at least 1 million years younger than the solar system. “A huge advance,” Bottke said. “My jaw was on the floor about that.”
Meanwhile, the hunt is on to interpret other meteorites in this new light. It’s amazing to think that samples on Earth originated near Saturn, Bottke says. “A few years ago if you had said that you would have had people laugh at you.”
Delays in the testing and integration of NASA’s next space observatory, the James Webb Space Telescope (JWST), will push its launch back to May 2020, the agency announced today. NASA’s acting administrator, Robert Lightfoot, also admitted in a press briefing that the project’s cost may exceed the ceiling of $8 billion imposed by Congress in 2011. The agency expects to provide a confirmed schedule and cost estimate this summer. Congress will have to give its approval for extra spending if the cost cap has been breached.
The two parts of the spacecraft—the telescope and instrument package and the spacecraft bus with sunshield—are waiting to be melded together at the facility of prime contractor Northrop Grumman in Redondo Beach, California. The JWST was originally planned to launch in October, but last September NASA pushed back the launch to the second quarter of 2019.
Delays in testing the sunshield and problems with the in-space propulsion system have slowed work. NASA science chief Thomas Zurbuchen said during the briefing that, during testing, the cables that tension the craft’s tennis court–size sunshield became unexpectedly slack during deployment and risked tangling. He also said the deployment tests had produced some tears in the superthin fabric of the sunshield that are now repaired and some changes had to be made to stem leaks in the propulsion system. “Webb is a really complex machine and rigorous testing is required to have a high confidence of success,” Zurbuchen said. “We have one shot to get this into space. Failure is not an option.”
A review board suggested that testing of the completed spacecraft will take longer than predicted, and calculated that there is a 70% probability the JWST would be ready for a May 2020 launch. In response, NASA will increase its engineering oversight, make some personnel changes, and institute new management reporting structures that will involve daily progress reports from Northrop Grumman. NASA has also commissioned an independent review of the project led by NASA veteran Thomas Young. That panel’s recommendations and NASA’s own findings will be combined in a report to be delivered to Congress this summer.
We propose that the state of the universe does not spontaneously violate CPT. Instead, the universe before the Big Bang is the CPT reflection of the universe after the bang. Phrased another way, the universe before the bang and the universe after the bang may be re-interpreted as a universe/anti-universe pair, created from nothing. CPT selects a unique vacuum state for the QFT on such a spacetime, which leads to a new perspective on the cosmological baryon asymmetry, and a new explanation for the observed dark matter abundance. In particular, if we assume that the matter fields in the universe are described by the standard model of particle physics (including right-handed neutrinos), we predict that one of the heavy neutrinos is stable, and that its density automatically matches the observed dark matter density if its mass is 4.8×108 GeV. Among other predictions, we have: (i) that the three light neutrinos are majorana; (ii) that the lightest of these is exactly massless; and (iii) that there are no primordial long-wavelength gravitational waves. We mention connections to the strong CP problem and the arrow of time.
We present and compare several cosmological constraints on the cross section for elastic scattering between dark matter (DM) and baryons, for cross sections with a range of power-law dependences on the DM-baryon relative velocity v, especially focusing on the case of σ ∝ v-4. We study constraints spanning a wide range of epochs in cosmological history, from pre-recombination distortions to the blackbody spectrum and anisotropies of the cosmic microwave background (CMB), to modifications to the intergalactic medium temperature and the resulting 21cm signal, and discuss the allowed signals in the latter channels given the constraints from the former. We improve previous constraints on DM-baryon scattering from the CMB anisotropies, demonstrate via principal component analysis that the effect on the CMB can be written as a simple function of DM mass, and map out the redshifts dominating this signal. We show that given high-redshift constraints on DM-baryon scattering, a v-4 scaling of the cross section for light DM would be sufficient to explain the deep 21cm absorption trough recently claimed by the EDGES experiment, if 100% of the DM scatters with baryons. For millicharged DM models proposed to explain the observation, where only a small fraction of the DM interacts, we estimate that a PIXIE-like future experiment measuring CMB spectral distortion could test the relevant parameter space.
THE WOODLANDS, TEXAS—What if aliens aren’t like us? For a long time, that’s been a confounding problem in the search for life beyond Earth: If alien life looks nothing like it does on our planet, if it abjures DNA and RNA for building blocks utterly strange, how could robotic explorers even know that they’ve discovered it?
With scientists eyeing the potentially habitable waters of Jupiter’s moon Europa and Saturn’s moon Enceladus, this question has only grown more pressing. It’s fine to think any life on Mars could have shared ancestry with Earth—the planets are close and have shared a lot of grist over billions of years—but DNA-based life at Saturn? That would be a stretch.
Still, the hunt for nonterran life could be accomplished with a tool familiar in any biology lab, scientists suggested here yesterday at the Lunar and Planetary Science Conference and in a paper in press at Astrobiology. If you want to have the broadest possible search for life, both terran and nonterran, they say, pack a genome sequencer. “You could have a completely different biochemistry,” says Sarah Stewart Johnson, an astrobiologist at Georgetown University in Washington, D.C., who led the work. “But you could still see a signal.”
The technique as proposed would work because nucleic acids like DNA are promiscuous. Take a strand 30 to 80 nucleotides long and it will naturally form secondary and tertiary structures that will bind with a host of materials and shapes: biologicals like peptides and proteins, sure, but also to organic molecules, minerals, and even metals.
Johnson’s team borrowed a technique from cancer biology, called the systematic evolution of ligands by exponential enrichment (SELEX), which creates a huge library of random, short chains of nucleotides, called aptamers, and then incubates them with a target of choice, such a specific breast cancer cell. SELEX is typically repeated multiple times, with scientists filtering out the aptamers that are not specific to their target.
“The idea here would be to flip that around,” Johnson says. Their sensor would expose samples to all those random aptamers, garnering information from each hit. “Analyze the whole binding pattern, anything that binds,” she says. These patterns could then be amplified and sequenced, revealing a pattern of chemical complexity that Johnson calls a fingerprint.
Such a fingerprint would not be as clear as catching DNA in a sequencer. But if a sample is exposed to such an aptamer library, a complex molecule is going to bind with a lot more sequences than a simple one. And complexity, especially if captured in a very small sample, is likely a hallmark of life. “It might not be as definitive as your DNA sequencer, but it could be, if not a biosignature, a really strong bioprint,”Johnson says.
This is not the only approach to agnostic life detection, as the nascent field is called, most of which require trading definitiveness for inclusivity. Johnson has worked with other scientists who have shown how a mass spectrometer, a tool common on NASA robotic missions right now, could be twinned with algorithms designed to evaluate a molecule’s complexity, not just its weight. Other techniques could gauge signs of mobility or energy use to flag nonterran life, Johnson adds, though those are not as technologically ready.
In recent years, genome sequencers have dramatically shrunk in size; Oxford Nanopore’s MinION, for example, weighs only 85 grams and fits in your hand. Although no NASA mission currently has plans to take a sequencer into space, the agency is supporting several efforts to get the technology ready for exploration.
Johnson’s proposal seems innovative and could complement other efforts at life detection, says Christopher Carr, an astrobiologist at the Massachusetts Institute of Technology in Cambridge who is not involved in the work. Carr is leading one of the NASA sequencing efforts, and Johnson’s technique could increase such a tool’s usefulness. “It will have a high likelihood to produce data for any given sample, whether or not it contains life,” he says. But the approach also carries the risk of providing confusing data, especially from unknown materials. Careful preparation and instruments that provide context for the sample could help overcome such hurdles, he adds.
Johnson, for one, is eager to get going with the hunt for life. She wants sequencers everywhere—not just on the outer planets, but also for samples of the Mars subsurface or Saturn’s moon Titan, dipped in frozen methane. “I want to go to Titan where everything is crazy and different,” she says. “I just want to go. I want to go everywhere.”
Modified Newtonian Dynamics has one free parameter and requires an interpolation function to recover the normal Newtonian limit. We here show that this interpolation function is unnecessary in a recently proposed covariant completion of Erik Verlinde’s emergent gravity, and that Verlinde’s approach moreover fixes the function’s one free parameter. The so-derived correlation between the observed acceleration (inferred from rotation curves) and the gravitational acceleration due to merely the baryonic matter fits well with data. We then argue that the redshift-dependence of galactic rotation curves could offer a way to tell apart different versions of modified gravity from particle dark matter.
Er en bog af Ray Kurzweil om kunstig intelligens. Endemålet kan hurtigt forklares ved Kurzweils svar på spørgsmålet: Does God exist? Not yet!
Bogen omhandler i virkeligheden “Livets oprindelse” og intelligensens efterfølgende frigørelse fra biologi og kemi.
Kurzweil says the law of accelerating returns suggests that once a civilization develops primitive mechanical technologies, it is only a few centuries before they achieve everything outlined in the book, at which point it will start expanding outward, saturating the universe with intelligence. Since people have found no evidence of other civilizations, Kurzweil believes humans are likely alone in the universe. Thus Kurzweil concludes it is humanity’s destiny to do the saturating, enlisting all matter and energy in the process.
Sådanne ideer er ikke nye inden for Science Fiction. SF-forfatteren:
In the 2010s public figures such as Stephen Hawking and Elon Musk expressed concern that full artificial intelligence could result in human extinction. The consequences of the singularity and its potential benefit or harm to the human race have been hotly debated.
In 2015, Singularity University and Yunus Social Business (YSB) announced a partnership at the World Economic Forum to use “accelerating technologies” and social entrepreneurship for global development in developing areas of the world where YSB is active.
Her er World Economic Forum særlig interessant:
The forum is best known for its annual meeting at the end of January in Davos, a mountain resort in Graubünden, in the eastern Alps region of Switzerland. The meeting brings together some 2,500 top business leaders, international political leaders, economists, celebrities and journalists for up to four days to discuss the most pressing issues facing the world. Often this location alone is used to identify meetings, participation, and participants, with such phrases as “a Davos panel” and “Davos man” being used.
Det er altså det erklærede formål med “Singularity University” at overbevise verdens ledere og økonomer om, at den kunstige intelligens inden for de kommende 30 år vil forvandle menneskeheden til Gud.
Her er så den officielle hjemmeside for Singularity University:
Modern whole-organism genome analysis, in combination with biomass estimates, allows us to estimate a lower bound on the total information content in the biosphere: 5.3 × 1031 (±3.6 × 1031) megabases (Mb) of DNA. Given conservative estimates regarding DNA transcription rates, this information content suggests biosphere processing speeds exceeding yottaNOPS values (1024 Nucleotide Operations Per Second). Although prokaryotes evolved at least 3 billion years before plants and animals, we find that the information content of prokaryotes is similar to plants and animals at the present day. This information-based approach offers a new way to quantify anthropogenic and natural processes in the biosphere and its information diversity over time.
The Total DNA in the Biosphere
Using information on the typical mass per cell for each domain and group and the genome size, we estimate the total amount of DNA in the biosphere to be 5.3 × 1031 (±3.6 × 1031) megabase pairs (Mb). This quantity corresponds to approximately 5 × 1010 tonnes of DNA, assuming that 978 Mb of DNA is equivalent to one picogram. Assuming the commonly used density for DNA of 1.7 g/cm3, then this DNA is equivalent to the volume of approximately 1 billion standard (6.1 × 2.44 × 2.44 m) shipping containers. The DNA is incorporated within approximately 2 × 1012 tonnes of biomass and approximately 5 × 1030 living cells, the latter dominated by prokaryotes. By analogy, it would require 1021 computers with the mean storage capacity of the world’s four most powerful supercomputers (Tianhe-2, Titan, Sequoia, and K computer) to store this information.
The Computational Power of the Biosphere
Finding the amount of DNA in the biosphere enables an estimate of the computational speed of the biosphere, in terms of the number of bases transcribed per second, or Nucleotide Operations Per Second (NOPS), analogous to the Floating-point Operations Per Second (FLOPS) metric used in electronic computing. A typical speed of DNA transcription is 18–42 bases per second for RNA polymerase II to travel along chromatin templates and elsewhere suggested as 100 bases per second. Precisely how much of the DNA on Earth is being transcribed at any one time is unknown. The percentage of any given genome being transcribed at any given time depends on the reproductive and physiological state of organisms, and at the current time we cannot reliably estimate this for all life on Earth. If all the DNA in the biosphere was being transcribed at these reported rates, taking an estimated transcription rate of 30 bases per second, then the potential computational power of the biosphere would be approximately 1015 yottaNOPS (yotta = 1024), about 1022 times more processing power than the Tianhe-2 supercomputer, which has a processing power on the order of 105 teraFLOPS (tera = 1012). It is estimated that at 37°C, about 25% of Open Reading Frames in Escherichia coli are being transcribed, but this is in a metabolically active population. In the natural environment, the percentage of DNA being transcribed is likely to be much less. Nevertheless, it is clear that even if the total DNA in the biosphere being transcribed at any given time was orders of magnitude less, the biosphere has many orders of magnitude more computational power than the fastest electronic computers yet built.
The elastic scattering between dark matter particles and photons represents an attractive possibility to solve a number of discrepancies between observations and standard cold dark matter predictions, as the induced collisional damping would imply a suppression of small-scale structures. We consider this scenario and confront it with measurements of the ionization history of the Universe at several redshifts and with recent estimates of the counts of Milky Way satellite galaxies. We derive a a conservative upper bound on the dark matter-photon elastic scattering cross section of σγDM < 8 × 10-10 σT (mDM/GeV) at 95% CL, about one order of magnitude tighter than previous findings. Due to the strong degeneracies with astrophysical parameters, the bound on the dark matter-photon scattering cross section derived here is driven by the estimate of the number of Milky Way satellite galaxies. Finally, we also argue that future 21~cm probes could help in disentangling among possible non-cold dark matter candidates, such as interacting and warm dark matter scenarios.