from the the-universe-is-weird dept.
A physicist is using a theory he advanced to explain how EmDrive could work to explain how dwarf galaxies can be held together without the requirement of dark matter:
British physicist Dr Mike McCulloch, who previously used quantised inertia to explain how the controversial electromagnetic space propulsion technology EmDrive works, says that he has new evidence showing his theory can also explain galaxy rotation, which is one of physics' biggest mysteries. McCulloch, a lecturer in geomatics at Plymouth University's school of marine science and engineering, says he now has even more evidence that his "new physics theory" about quantised inertia works, and that it makes it possible to explain why galaxies are not ripped apart without using theory of dark matter.
[...] There are 20 dwarf galaxies in existence from Segue-1 (the smallest) to Canes Venatici-1 (the largest), and dark matter is only meant to work by spreading out across a wide distance, but it is still used to explain dwarf galaxies, even though this requires dark matter to be concentrated within these systems, which is implausible. Instead, McCulloch asserts that quantised inertia can be used to explain how galaxies rotate without using dark matter, and he has written a paper that has been accepted by the bi-monthly peer reviewed journal Astrophysics and Space Science.
Reprint of the IBT link here.
From the abstract of Low-acceleration dwarf galaxies as tests of quantised inertia (DOI not yet published):
Dwarf satellite galaxies of the Milky Way appear to be gravitationally bound, but their stars' orbital motion seems too fast to allow this given their visible mass. This is akin to the larger-scale galaxy rotation problem. In this paper, a modification of inertia called quantised inertia or MiHsC (Modied inertia due to a Hubble-scale Casimir effect) which correctly predicts larger galaxy rotations without dark matter is tested on eleven dwarf satellite galaxies of the Milky Way, for which mass and velocity data are available. Quantised inertia slightly outperforms MoND (Modied Newtonian Dynamics) in predicting the velocity dispersion of these systems, and has the fundamental advantage over MoND that it does not need an adjustable parameter.
Previously: Study Casts Doubt on Cosmic Acceleration and Dark Energy
Dark Matter Beats its Latest Challenge
Emergent Gravity and the Dark Universe
Space Race 2.0: China May Already be Testing an EmDrive in Orbit
Milky Way is Not Only Being Pulled—It's Also "Pushed" by a Void
A newly published analysis of Type Ia supernovae calls into question the accelerating expansion of the universe and the existence of dark energy:
Five years ago, the Nobel Prize in Physics was awarded to three astronomers for their discovery, in the late 1990s, that the universe is expanding at an accelerating pace. Their conclusions were based on analysis of Type Ia supernovae – the spectacular thermonuclear explosions of dying stars – picked up by the Hubble space telescope and large ground-based telescopes. It led to the widespread acceptance of the idea that the universe is dominated by a mysterious substance named 'dark energy' that drives this accelerating expansion.
Now, a team of scientists led by Professor Subir Sarkar of Oxford University's Department of Physics has cast doubt on this standard cosmological concept. Making use of a vastly increased data set – a catalogue of 740 Type Ia supernovae, more than ten times the original sample size – the researchers have found that the evidence for acceleration may be flimsier than previously thought, with the data being consistent with a constant rate of expansion.
Marginal evidence for cosmic acceleration from Type Ia supernovae (open, DOI: 10.1038/srep35596) (DX)
Last month, a team of scientists led by Stacy McGaugh at Case Western Reserve University determined from observations of 153 galaxies that the dynamics of galaxy rotation seems to depend solely on the normal, visible matter in it (SN coverage here). It was a strong argument that rather than hypothesising dark matter to explain the oddities in galactic rotation, it may instead be necessary to modify the laws of gravity.
However, two scientists from McMaster University, Ben Keller and James Wadsley, have just recently examined the results of a detailed simulation of dark matter in galaxy formation previously done known as the McMaster Unbiased Galaxy Simulations 2 (MUGS2). The simulation was a sophisticated one that took into account various other factors such as gas dynamics, star formation, and stellar feedback, but incorporated no new physics beyond that of the standard Lambda-Cold Dark Matter (ΛCDM) cosmological model. They found that the relation that McGaugh et. al. discovered from observations of real galaxies was reproduced just about exactly by the simulation. Their paper is here. Their abstract states:
Recent analysis (McGaugh et al. 2016) of the SPARC galaxy sample found a surprisingly tight relation between the radial acceleration inferred from the rotation curves, and the acceleration due to the baryonic components of the disc. It has been suggested that this relation may be evidence for new physics, beyond ΛCDM. In this letter we show that the 18 galaxies from the MUGS2 match the SPARC acceleration relation. These cosmological simulations of star forming, rotationally supported discs were simulated with a WMAP3 ΛCDM cosmology, and match the SPARC acceleration relation with less scatter than the observational data. These results show that this acceleration law is a consequence of dissipative collapse of baryons, rather than being evidence for exotic dark-sector physics or new dynamical laws.
So now it seems that the earlier troubles with dark matter were actually the result of too naïve a simulation, and by taking into account additional known, relevant physics, the troubles disappear.
Theoretical physicist Eric Verlinde has finally published his much anticipated article on the nature of gravity. In a 2010 New York Times article Verlinde already stated: gravity is an illusion. His theory goes beyond the concept of gravity as envisioned by both Isaac Newton and Albert Einstein. It will be very interesting to see other scientists sink their teeth into this.
Abstract of his article:
Recent theoretical progress indicates that spacetime and gravity emerge together from the entanglement structure of an underlying microscopic theory. These ideas are best understood in Anti-de Sitter space, where they rely on the area law for entanglement entropy. The extension to de Sitter space requires taking into account the entropy and temperature associated with the cosmological horizon. Using insights from string theory, black hole physics and quantum information theory we argue that the positive dark energy leads to a thermal volume law contribution to the entropy that overtakes the area law precisely at the cosmological horizon. Due to the competition between area and volume law entanglement the microscopic de Sitter states do not thermalise at sub-Hubble scales: they exhibit memory effects in the form of an entropy displacement caused by matter. The emergent laws of gravity contain an additional 'dark' gravitational force describing the 'elastic' response due to the entropy displacement. We derive an estimate of the strength of this extra force in terms of the baryonic mass, Newton's constant and the Hubble acceleration scale a0 = cH0, and provide evidence for the fact that this additional 'dark gravity force' explains the observed phenomena in galaxies and clusters currently attributed to dark matter.
Heck, I'm not even going to pretend I grok any of this: I shine shoes for a living and just hope that my understanding of gravity-as-we-know-it is sufficient to catch the coins customers drop into my weary hand.
[Researchers] in China have announced that they've already been testing the controversial drive in low-Earth orbit, and they're looking into using the EM Drive to power their satellites as soon as possible.
Big disclaimer here - all we have to go on right now is a press conference announcement [archive.is] and an article from a government-sponsored Chinese newspaper (and the country doesn't have the best track record when it comes to trustworthy research).
[...] But what the China Academy of Space Technology (CAST) team is saying also corresponds with information provided to IB Times from an anonymous source. According to their informant, China already has an EM Drive on board its version of the International Space Station, the space laboratory Tiangong-2.
You may not notice it, but our Milky Way galaxy is cruising along at 630 kilometers (~391 miles) per second. That speed is often attributed to the influence of a single gravitational source. But in a new study, a group of researchers has found that the motions of the Local Group—the cluster of galaxies that includes the Milky Way—are being driven by two primary sources: the previously known and incredibly massive Shapley Supercluster and a newly discovered repeller, which the researchers dub the Dipole Repeller.
Shapley's contribution was already known, but the Dipole Repeller's hadn't been recognized prior to this study.
The researchers plotted the motions of many galaxies in the nearby Universe in a 3D model, using data from the Cosmicflows-2 database. Since the Universe is expanding, most galaxies are moving away from ours, creating a red-shift in the light they emit. But since the researchers were more interested in the other influences on a galaxy's motion, they simply subtracted the expansion's contribution. The resulting plot shows what the motions of galaxies would look like if space wasn't expanding.
The galaxies in that plot all follow different paths—some proceed through the Great Attractor in the middle of the picture, others curve around the periphery, and so on. They all seemed to have a clear destination: the Shapley Supercluster. But they also seem to have a clear origin point: the Dipole Repeller. When the researchers traced the galaxies' paths backwards, they all originate there. It looks a lot like there's something there repelling the galaxies, as if the Repeller and Shapley formed the negative and positive ends of an electrical dipole, and charges were being driven from one to the other.
That's not what's actually happening. Gravity is the dominant force acting on a galaxy, and gravity, unlike electricity, can't repel—it's only an attractive force. So what's going on?
The Dipole Repeller's true identity is probably, well, nothing. It's actually a void with much less mass than the surrounding space. This has the effect of seeming like a repeller because the nearby space has a much denser concentration of matter, creating a gravitational gradient between the two. The low-density void is the only direction from which there's no force pulling on the galaxy, or at least significantly less force than comes from every other direction.
Nature Astronomy, 2017. DOI: 10.1038/s41550-016-0036
The man behind the disputed thruster technology EmDrive has published a presentation detailing the third generation of the device. Roger Shawyer envisions EmDrive 3.0 enabling personal flying vehicles and a "space elevator without cables":
[Although] the second generation of the EmDrive can theoretically produce 3 tonnes of thrust for 1 kilowatt of power, it isn't able to move very far, so it is only useful for marine applications or for diverting asteroids, like in the new CBS sci-fi TV drama Salvation.
Shawyer has long said that his aim for inventing the EmDrive was to help get satellites into space cheaply, to enable more applications and new ways for the human race to combat global warming and the energy crisis. Essentially, the EmDrive needs to be able to move and work as well as a conventional rocket, in order to be a viable solution.
To negate these shortfalls, Shawyer's firm Satellite Propulsion Research Ltd (SPR) has also been researching a third generation of the EmDrive, which solved the acceleration problem by reducing the specific thrust.
So instead of getting 3 tonnes of thrust for every kilowatt, substantially less thrust is produced – but it can be used to accelerate the device (more about this theory can be read in a paper Shawyer presented in Beijing in 2013).
Speaking of that TV show, Roger would like some credit please.
Previously: Finnish Physicist Says EmDrive Device Does Have an Exhaust
It's Official: NASA's Peer-Reviewed EmDrive Paper Has Finally Been Published
Space Race 2.0: China May Already be Testing an EmDrive in Orbit
Physicist Uses "Quantised Inertia" to Explain Both EmDrive and Galaxy Rotation