Saturn’s rotation in three different infrared wavelengths.
Credit: Cassini-Huygens mission/JPL/Space Science Institute
These intense false-color views highlight and enhance color variations across the intensely cratered and cracked surface of Rhea.
To create the false-color view, ultraviolet, green and infrared images were combined into a single black and white picture that isolates and maps regional color differences. This “color map” was then superposed over a clear-filter image. The origin of the color differences is not yet understood, but may be caused by subtle differences in the surface composition or the sizes of grains making up the icy soil.
Credit: NASA/JPL/Space Science Institute
The Southern Lights - the Aurora Australis - as seen from the Suomi NPP Earth-observing satellite. (via)
It could be time to bid the Big Bang bye-bye. Cosmologists have speculated that the Universe formed from the debris ejected when a four-dimensional star collapsed into a black hole — a scenario that would help to explain why the cosmos seems to be so uniform in all directions.
The standard Big Bang model tells us that the Universe exploded out of an infinitely dense point, or singularity. But nobody knows what would have triggered this outburst: the known laws of physics cannot tell us what happened at that moment.
“For all physicists know, dragons could have come flying out of the singularity,” says Niayesh Afshordi, an astrophysicist at the Perimeter Institute for Theoretical Physics in Waterloo, Canada.
It is also difficult to explain how a violent Big Bang would have left behind a Universe that has an almost completely uniform temperature, because there does not seem to have been enough time since the birth of the cosmos for it to have reached temperature equilibrium.
To most cosmologists, the most plausible explanation for that uniformity is that, soon after the beginning of time, some unknown form of energy made the young Universe inflate at a rate that was faster than the speed of light. That way, a small patch with roughly uniform temperature would have stretched into the vast cosmos we see today. But Afshordi notes that “the Big Bang was so chaotic, it’s not clear there would have been even a small homogenous patch for inflation to start working on”.
On the brane
In a paper posted last week on the arXiv preprint server, Afshordi and his colleagues turn their attention to a proposal made in 2000 by a team including Gia Dvali, a physicist now at the Ludwig Maximilians University in Munich, Germany. In that model, our three-dimensional (3D) Universe is a membrane, or brane, that floats through a ‘bulk universe’ that has four spatial dimensions.
Ashfordi’s team realized that if the bulk universe contained its own four-dimensional (4D) stars, some of them could collapse, forming 4D black holes in the same way that massive stars in our Universe do: they explode as supernovae, violently ejecting their outer layers, while their inner layers collapse into a black hole.
In our Universe, a black hole is bounded by a spherical surface called an event horizon. Whereas in ordinary three-dimensional space it takes a two-dimensional object (a surface) to create a boundary inside a black hole, in the bulk universe the event horizon of a 4D black hole would be a 3D object — a shape called a hypersphere. When Afshordi’s team modelled the death of a 4D star, they found that the ejected material would form a 3D brane surrounding that 3D event horizon, and slowly expand.
The authors postulate that the 3D Universe we live in might be just such a brane — and that we detect the brane’s growth as cosmic expansion. “Astronomers measured that expansion and extrapolated back that the Universe must have begun with a Big Bang — but that is just a mirage,” says Afshordi.
The total amount of energy in the universe is constant. Energy cannot be created or destroyed but only converted from one form into another. If an object or process gains an amount of energy, it does so at the expense of a loss in energy somewhere else in the universe.
First Law of Thermodynamics
but maybe also the First Law of How Life Works.
The color of the Aurora depends on the altitude and the atom being struck by solar radiation (causing excitation). At higher altitudes, there is more Atomic Oxygen than Nitrogen, leading to the common color stratifications you see.
500-200 km altitude
— Atomic Oxygen — Red
— Atomic Oxygen — Greenish-Yellow
— Ionized Nitrogen — Blue/Purple
— Nitrogen (N2) — Crimson
Oxygen only emits red at higher altitudes because once it’s excited, it takes a longer time to emit red than it does green. Why is that important? Well, at lower altitudes there is more Nitrogen for the Oxygen to bump into and absorb that excitation-energy before it gets a chance to emit red light. In this case, where the collision occurs, the Oxygen will emit Green and at low enough altitudes the Nitrogen-Oxygen collisions eventually prevent Oxygen from emitting any light at all.
During stronger storms, high energy solar particles will reach lower in the atmosphere and cause the Crimson emission from Nitrogen, creating a deep-red band at the lower edge of the aurora. Other elements emit light too, like Hydrogen (Blue) or Helium (Purple) which are at higher altitudes.
Fluid dynamics of Earth’s ocean, colored by surface temperature.
shine on forever, shine on benevolent sun