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Huge microwave observatory to search for cosmic inflation

Multi-telescope project has ambitious goals and a big price tag.

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NSF/Steffen Richter/Harvard Univ./SPL

Telescopes in Antarctica track the cosmic microwave background radiation left over from the Big Bang.

US researchers have drafted plans to study the faint afterglow of the Big Bang using a new facility. They hope it will be sensitive enough to confirm whether or not the infant Universe underwent a brief period of explosive expansion known as inflation.

The Cosmic Microwave Background Stage-4 experiment (CMB-S4) would comprise three 6-metre and 14 half-metre telescopes distributed across two sites in Antarctica and Chile, according to a preliminary design due to be made public this week. Potentially up and running within a decade, the facility would be nearly 100 times as sensitive as existing ground-based CMB experiments.

It won’t be cheap, however. Construction will cost a little over US$400 million, according to the expert task force commissioned by the US Department of Energy (DOE) and National Science Foundation (NSF) to produce the design. That is at least twice as much as envisioned in a less-detailed review 3 years ago, and 30 times the cost of existing experiments.

The price tag is “not necessarily” a showstopper, says Richard Barvainis, who directs the NSF’s extragalactic astronomy and cosmology programme. But CMB-S4 will have to compete for limited funding with other large proposed facilities.

Primordial ripples

The CMB provides an image of the Universe as it was just 380,000 years after the Big Bang. Discovered in 1964, the radiation has since been observed by experiments on the ground, on balloons and in space, yielding increasingly precise insights into the Universe’s geometry, contents and age — currently calculated at a little under 14 billion years.

But physicists think that the CMB has more to offer. In particular, distinctive patterns in its polarization known as B modes could reveal the existence of primordial gravitational waves. Gravitational waves — ripples in space-time — were first observed directly in 2015, but their detection in the very early Universe would be a major breakthrough, providing the strongest evidence yet for inflation, according to Charles Lawrence, an astrophysicist at NASA’s Jet Propulsion Laboratory in Pasadena, California, who chairs the CMB-S4 task force.

Current ground-based CMB experiments typically detect microwaves using a few thousand pixels and are based either near the South Pole or in Chile’s Atacama Desert, where very dry conditions make the atmosphere nearly transparent to microwave radiation. None of the experiments has so far spotted the telltale B mode. One group did make a well-publicized claim in 2014, but it transpired that the sighting was actually caused by emissions from Galactic dust. Researchers are now building several more experiments that will be ten times as sensitive.

But Lawrence says that detecting the gravitational waves predicted by many of today’s models of inflation would require sensitivity boosted by a further order of magnitude. Hence CMB-S4, which would comprise nearly 400,000 pixels. If it, too, came up empty-handed, the task force writes, it might be necessary “to give up on inflation”.

Fight for funding

CMB-S4 is too large for any single group to build, so researchers across the US started collaborating on the design in 2013. Their initial plans were approved a year later by a panel advising the DOE on particle physics. But they must wait until 2020 to see how they fare in the next round of the once-per-decade survey of astronomy and astrophysics that the NSF uses to assess funding priorities.

Barvainis says that the agency will support CMB-S4 only if it gets “a very high priority” in the decadal survey, which is also likely to include a proposed upgrade to the National Radio Astronomy Observatory’s Very Large Array in New Mexico, along with the development of one or more large optical telescopes. Even if the project does prevail, he adds, further agency reviews could delay the envisaged start of operations — due in 2026 — by at least two years.

The task force suggests that instead, CMB-S4 could be started by adding DOE detectors to existing telescopes in Chile while installing a few of the smaller telescopes at the South Pole. Under that strategy, the NSF would initially fund only operations. However, officials at the DOE also foresee snags. James Siegrist, the agency’s associate director for high-energy physics, says budgetary disagreements between the White House and Congress are creating “a lot of uncertainty” in Washington DC. A delay until 2027 or 2028 “could easily happen”, he predicts.

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  1. Avatar for Pentcho Valev
    Pentcho Valev
    Vacuum is not empty, and this makes the Cosmic Microwave Background concept rather silly. It is unreasonable to believe that the vacuum is full of energy and at the same time to claim that the noise known as CMB is not a product of this energy but just traverses it, unchanged. You have vacuum energy, detectors in contact with the vacuum which register strange noise coming from all directions, and you conclude that the noise is not produced by the vacuum energy but comes from the miraculous beginning of space and time. In addition, you implicitly assume that the vacuum energy does not change the noise. Silly, isn't it? Vacuum slows down light - this explains the Hubble redshift (in a STATIC universe): "...explains Liberati. "If spacetime is a kind of fluid, then we must also take into account its viscosity and other dissipative effects, which had never been considered in detail". Liberati and Maccione catalogued these effects and showed that viscosity tends to rapidly dissipate photons and other particles along their path, "And yet we can see photons travelling from astrophysical objects located millions of light years away!" he continues. "If spacetime is a fluid, then according to our calculations it must necessarily be a superfluid. This means that its viscosity value is extremely low, close to zero"." Nature: "As waves travel through a medium, they lose energy over time. This dampening effect would also happen to photons traveling through spacetime, the researchers found." "Some physicists, however, suggest that there might be one other cosmic factor that could influence the speed of light: quantum vacuum fluctuation. This theory holds that so-called empty spaces in the Universe aren't actually empty - they're teeming with particles that are just constantly changing from existent to non-existent states. Quantum fluctuations, therefore, could slow down the speed of light." The transition from expanding to STATIC universe is unavoidable because the implications of the expanding universe theory are absurd: Sabine Hossenfelder: "If The Universe Is Expanding, Then Why Aren't We? The solution of general relativity that describes the expanding universe is a solution on average; it is good only on very large distances. But the solutions that describe galaxies are different - and just don't expand. It's not that galaxies expand unnoticeably, they just don't. The full solution, then, is both stitched together: Expanding space between non-expanding galaxies." "The Multiverse Is Inevitable, And We're Living In It. Alan Guth: "It's hard to build models of inflation that don't lead to a multiverse. It's not impossible, so I think there's still certainly research that needs to be done. But most models of inflation do lead to a multiverse, and evidence for inflation will be pushing us in the direction of taking [it] seriously." The Multiverse itself may not give rise to any observable, testable predictions, but arises as a direct consequences of other physical theories that have already been validated." Pentcho Valev
  2. Avatar for Pentcho Valev
    Pentcho Valev
    In my view, the following dialog marks the beginning of a sweeping revolution in cosmology: Sabine Hossenfelder: "Is Space-Time Fluid? We have known at least since Einstein that space and time are inseparable, two hemispheres of the same cosmic brain, joined to a single entity: space-time. Einstein also taught us that space-time isn't flat, like paper, but bent and wiggly, like a rubber sheet. Space-time curves around mass and energy and this gives rise to the effect we call gravity. That's what Einstein said. But turns out... [...] That space itself isn't fundamental but made of other things is one way to approach the problem. Not everyone likes the idea. What irks physicists most about giving substance to space-time is that this breaks Einstein's bond between space and time which has worked dramatically well - so far. Only further experiment will reveal whether Einstein's theory holds up." Arun: "How does a fluid analog of general relativity avoid having a preferred reference frame?" Sabine Hossenfelder: "Arun, it doesn't. It's why I write it breaks the union between space and time." [END OF QUOTATION] Sabine Hossenfelder is on the right track. The "preferred reference frame" does not affect the validity of the principle of relativity in its traditional usage - it is only responsible for the vacuum friction that slows down photons coming from distant stars, in a STATIC universe. So the Hubble redshift is produced, but at the end of their journey photons redshift less vigorously than at the beginning. This has wrongly been interpreted as accelerating expansion: "In the mid 1990s two teams of scientists, one led by Brian Schmidt and Adam Riess, and the other by Saul Perlmutter, independently measured distances to Type 1a supernovae in the distant universe, finding that they appeared to be further way than they should be if the universe's rate of expansion was constant. The observations led to the hypothesis that some kind of dark energy anti-gravitational force has caused the expansion of the universe to accelerate over the past six billion years." Below I'm showing that the redshifting varies EXPONENTIALLY with time. The "finding that they appeared to be further way than they should be" is an illusion due to using an approximation to the exponential function. Assume that, as the photon travels through space (in a STATIC universe), a factor equivalent to vacuum friction (see relevant references below) slows it down so that the photon loses speed in much the same way that a golf ball loses speed due to the resistance of the air. On this hypothesis the resistive force (Fr) is proportional to the speed of the photon (V): Fr = - KV That is, the speed of light decreases with time in accordance with the equation: dV/dt = - K'V Clearly, at the end of a very long journey of photons (coming from a very distant object), the contribution to the redshift is much smaller than the contribution at the beginning of the journey. Light coming from nearer objects is less subject to this effect, that is, the increase of the redshift with distance is closer to LINEAR for short distances. For distant light sources we have: f' = f(exp(-kt)) where f is the initial and f' the measured (redshifted) frequency. For short distances the following approximations can be made: f' = f(exp(-kt)) ~ f(1-kt) ~ f - kd/λ where d is the distance between the light source and the observer and λ is the wavelength. The approximate equation, f' = f - kd/λ, is only valid for short distances and corresponds to the Hubble law. The original equation, f' = f(exp(-kt)), shows that at the end of a very long journey (in a STATIC universe) photons redshift much less vigorously than at the beginning of the journey. This means that photons coming from very distant objects have undergone some initial "vigorous" redshifting which is unaccounted for by the Hubble law. This explains why the very distant objects "appeared to be further way than they should be if the universe's rate of expansion was constant". Is there "vacuum friction" that slows down photons? Yes there is: "This leads to the prediction of vacuum friction: The quantum vacuum can act in a manner reminiscent of a viscous fluid." New Scientist: "Vacuum has friction after all." "So how can a vacuum carry force? One of the first things we learn in classical physics is that in a perfect vacuum - a place entirely devoid of matter - friction can't exist, because empty space can't exert a force on objects traveling through it. But, in recent years, quantum physicists have shown that vacuums are actually filled by tiny electromagnetic fluctuations that can interfere with the activity of photons - particles of light - and produce a measurable force on objects." Pentcho Valev
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