plancke

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Theories about the Origins of Space and Time.

1. Gravity as Thermodynamics
Entropic gravity is a theory in modern physics that describes gravity as an entropic force - not a fundamental interaction mediated by a quantum field theory and a gauge particle, but a consequence of physical systems’ tendency to increase their entropy. 

2. Loop Quantum Gravity
According to Einstein, gravity is not a force – it is a property of space-time itself. Loop quantum gravity is an attempt to develop a quantum theory of gravity based directly on Einstein’s geometrical formulation. The main output of the theory is a physical picture of space where space is granular. More precisely, space can be viewed as an extremely fine fabric or network “woven” of finite loops. These networks of loops are called spin networks. The evolution of a spin network over time is called a spin foam. The predicted size of this structure is the Planck length, which is approximately 10−35 meters. According to the theory, there is no meaning to distance at scales smaller than the Planck scale. Therefore, LQG predicts that not just matter, but space itself, has an atomic structure.

3. Causal Sets
Its founding principles are that spacetime is fundamentally discrete and that spacetime events are related by a partial order. The theory postulates that the building blocks of space-time are simple mathematical points that are connected by links, with each link pointing from past to future. Such a link is a bare-bones representation of causality, meaning that an earlier point can affect a later one, but not vice versa. The resulting network is like a growing tree that gradually builds up into space-time.

4. Causal Dynamical Triangulations
The idea is to approximate the unknown fundamental constituents with tiny chunks of ordinary space-time caught up in a roiling sea of quantum fluctuations, and to follow how these chunks spontaneously glue themselves together into larger structures. The space-time building blocks were simple hyper-pyramids (four-dimensional counterparts to three-dimensional tetrahedrons) and the simulation’s gluing rules allowed them to combine freely. The result was a series of bizarre ‘universes’ that had far too many dimensions (or too few), and that folded back on themselves or broke into pieces.

5. Holography
In this model, the three-dimensional interior of the universe contains strings and black holes governed only by gravity, whereas its two-dimensional boundary contains elementary particles and fields that obey ordinary quantum laws without gravity. Hypothetical residents of the three-dimensional space would never see this boundary, because it would be infinitely far away. But that does not affect the mathematics: anything happening in the three-dimensional universe can be described equally well by equations in the two-dimensional boundary, and vice versa.

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Where is the cosmic microwave background?

“So the CMB isn’t the end of the Universe, but rather the limit of what we can see, both distance-wise (as far as we can go) and time-wise (as far back as we can go). Until we can directly detect the signatures of what was released earlier – the cosmic neutrino background, gravitational waves from inflation, etc. – the CMB will be our window into the earliest time we can observe: 380,000 years after the Big Bang.”

The farther away in space we look, the farther back in time we’re seeing. Light arriving from a star ten light years away is ten years old; light that took a billion-year journey from a distant galaxy is a billion years old. If we look out today at the most distant light we can see, we discover that it originates from the Big Bang itself: the Cosmic Microwave Background, or CMB. But this doesn’t mean the light has never interacted with anything since the birth of the observable Universe. In fact, many arose from matter/antimatter annihilations, all of them have scattered off of charged particles, and the CMB photons we detect today were all released when the Universe was a few hundred thousand years old. Because of the way the Big Bang works, the particles are literally everywhere, all at once, including right here.

Come get the full story on where the CMB actually is, and what it means when we state its age and distance!

As a man who has devoted his whole life to the most clear headed science, to the study of matter, I can tell you as a result of my research about atoms this much: There is no matter as such. All matter originates and exists only by virtue of a force which brings the particle of an atom to vibration and holds this most minute solar system of the atom together. We must assume behind this force the existence of a conscious and intelligent mind. This mind is the matrix of all matter.
—  Max Planck
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Mostly Mute Monday: Stunning Pictures Of The Milky Way’s Magnetic Field

“From the light’s polarization, we can reconstruct the galaxy’s magnetic field. And by superimposing it over the foreground emission map, we can see for the first time how our galaxy’s structure and magnetic field are interrelated. What we found was an intricate relationship between dust grains — the precursors to stars – and the giant magnetic structures we find, some of which extend for over a thousand light years in diameter.”

If you want to view the Milky Way in all its true splendor, you need to go beyond visible light, as the cosmic dust that gives rise to new stars also absorbs visible light, robbing us of a view of our galaxy. But those other wavelengths that are more transparent to the dust — infrared and microwave — are absorbed by Earth’s atmosphere. If we want to see what’s going on, we’ve got to go to space. With nine different frequency maps covering the entire sky, the ESA’s Planck satellite not only can determine what’s through that dust, but it can measure the effects of the Milky Way’s magnetic field due to the polarization of light, showing the future of star birth in our own galaxy.

After a short hiatus while we worked to figure it out, our Mostly Mute Monday series is back!

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Distant Quasars Show That Fundamental Constants Never Change

“From a physics perspective, it’s long been assumed that the fundamental constants and the laws of nature really are the same everywhere and at all times. However, one particular dimensionless constant, α, the ratio between the electric charge, the speed of light and the Planck constant, has been shown by a number of previous studies to show variations both the farther back in time we look and at different locations on the sky. However, new observations by a team working at Arecibo observatory, of the quasar PKS 1413+135, have placed a very tight constraint on the time variations, casting doubt on the previous findings. To only 1.3 parts in a million, the fundamental constant α once again appears to be truly constant.”

We assume that the fundamental constants are truly constant, but they don’t have to be. The speed of light is the same everywhere, but it could have been different elsewhere, either in space or in time. The same is true for other constants, like Planck’s constant, the gravitational constant, or even the fundamental charges or masses of particles. You might not think it’s likely, but the evidence indicated otherwise. Over the past 20 years, time variations and spatial variations in the fine structure constant, which determines the force of the electromagnetic coupling, have been observed to about 5 parts in a million in different locations and at different distances. It was a disputed but intriguing finding, but new evidence was just released conflicting with those results. Instead, the fundamental constant, α, once again appears to be truly constant, to better than 1.3 parts in a million, thanks to the new results from Arecibo.

There’s always more work to be done, but one of the greatest puzzling results from the astrophysical community might not be a puzzle after all!

There’s a temperature called the Planck temperature that is so hot that it straight up fucks with physics and doesn’t even qualify as a temperature and that’s why I honestly think this entire universe shitposts

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The first Milky Way hydrogen map reveals how stars were formed

Using a 100-meter radio telescope at Germany’s Max Planck Institute and Australia’s 64-meter CSIRO radio telescope — two of the world’s largest and most powerful telescopes — scientists were able to create a hydrogen map of the Milky Way. And they found the fuel for stars.

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Supporting the damaged brain

A new study shows that embryonic nerve cells can functionally integrate into local neural networks when transplanted into damaged areas of the visual cortex of adult mice.

(Image caption: Neuronal transplants (blue) connect with host neurons (yellow) in the adult mouse brain in a highly specific manner, rebuilding neural networks lost upon injury. Credit: Sofia Grade, LMU/Helmholtz Zentrum München)

When it comes to recovering from insult, the adult human brain has very little ability to compensate for nerve-cell loss. Biomedical researchers and clinicians are therefore exploring the possibility of using transplanted nerve cells to replace neurons that have been irreparably damaged as a result of trauma or disease. Previous studies have suggested there is potential to remedy at least some of the clinical symptoms resulting from acquired brain disease through the transplantation of fetal nerve cells into damaged neuronal networks. However, it is not clear whether transplanted intact neurons can be sufficiently integrated to result in restored function of the lesioned network. Now researchers based at LMU Munich, the Max Planck Institute for Neurobiology in Martinsried and the Helmholtz Zentrum München have demonstrated that, in mice, transplanted embryonic nerve cells can indeed be incorporated into an existing network in such a way that they correctly carry out the tasks performed by the damaged cells originally found in that position. Such work is of importance in the potential treatment of all acquired brain disease including neurodegenerative illnesses such as Alzheimer‘s or Parkinson’s disease, as well as strokes and trauma, given each disease state leads to the large-scale, irreversible loss of nerve cells and the acquisition of a what is usually a lifelong neurological deficit for the affected person.

In the study published in Nature, researchers of the Ludwig Maximilians University Munich, the Max Planck Institute of Neurobiology, and the Helmholtz Zentrum München have specifically asked whether transplanted embryonic nerve cells can functionally integrate into the visual cortex of adult mice. “This region of the brain is ideal for such experiments,” says Magdalena Götz, joint leader of the study together with Mark Hübener. Hübener is a specialist in the structure and function of the mouse visual cortex in Professor Tobias Bonhoeffer’s Department (Synapses – Circuits – Plasticity) at the MPI for Neurobiology. As Hübener explains, “we know so much about the functions of the nerve cells in this region and the connections between them that we can readily assess whether the implanted nerve cells actually perform the tasks normally carried out by the network.” In their experiments, the team transplanted embryonic nerve cells from the cerebral cortex into lesioned areas of the visual cortex of adult mice. Over the course of the following weeks and months, they monitored the behavior of the implanted, immature neurons by means of two-photon microscopy to ascertain whether they differentiated into so-called pyramidal cells, a cell type normally found in the area of interest. “The very fact that the cells survived and continued to develop was very encouraging,” Hübener remarks. “But things got really exciting when we took a closer look at the electrical activity of the transplanted cells.” In their joint study, PhD student Susanne Falkner and Postdoc Sofia Grade were able to show that the new cells formed the synaptic connections that neurons in their position in the network would normally make, and that they responded to visual stimuli.

The team then went on to characterize, for the first time, the broader pattern of connections made by the transplanted neurons. Astonishingly, they found that pyramidal cells derived from the transplanted immature neurons formed functional connections with the appropriate nerve cells all over the brain. In other words, they received precisely the same inputs as their predecessors in the network. In addition, they were able to process that information and pass it on to the downstream neurons which had also differentiated in the correct manner. “These findings demonstrate that the implanted nerve cells have integrated with high precision into a neuronal network into which, under normal conditions, new nerve cells would never have been incorporated,” explains Götz, whose work at the Helmholtz Zentrum and at LMU focuses on finding ways to replace lost neurons in the central nervous system. The new study reveals that immature neurons are capable of correctly responding to differentiation signals in the adult mammalian brain and can close functional gaps in an existing neural network.