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Category: cosmology

The Physicist Who Proved Entropy = Gravity

What if gravity is not fundamental but emerges from quantum entanglement? In this episode, physicist Ted Jacobson reveals how Einstein’s equations can be derived from thermodynamic principles of the quantum vacuum, reshaping our understanding of space, time, and gravity itself.

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Gravitational waves leave imprints on light emitted by atoms, theoretical study predicts

Gravitational waves are ripples in spacetime produced by violent cosmic events, such as the merging of black holes. So far, direct detections have relied on measuring tiny distance changes over kilometer-scale instruments. In a new theoretical study published in Physical Review Letters, researchers at Stockholm University, Nordita, and the University of Tübingen propose an unconventional approach: tracking how gravitational waves reshape the light emitted by atoms. The work describes a possible detection route, but an experimental demonstration remains for the future.

When atoms are excited, they naturally relax by emitting light at a characteristic frequency—a quantum process known as spontaneous emission. This happens through their interaction with the quantum electromagnetic field.

“Gravitational waves modulate the quantum field, which in turn affects spontaneous emission,” said Jerzy Paczos, a Ph.D. student at Stockholm University. “This modulation can shift the frequencies of emitted photons compared with the no-wave case.”

DESI maps C-19, an extremely metal-poor Milky Way stellar stream

Using the Mayall 4-meter telescope at Kitt Peak National Observatory, an international team of astronomers has observed C-19—an extremely metal-poor stellar stream in the Milky Way’s halo. Results of the observational campaign, published March 11 on the arXiv pre-print server, provide crucial insights into the properties of this stellar stream.

Stellar streams are remnants of dwarf galaxies or globular clusters (GCs) that once orbited a galaxy but have been disrupted and stretched out along their orbits by tidal forces of their hosts. Observations show that many stellar streams are elongated debris of tidally disrupted globular clusters.

Studies of galactic stellar streams could answer some crucial questions about the Milky Way. For instance, they could help us understand the large-scale mass distribution of the galactic dark matter halo. Moreover, the investigation of stellar streams could confirm whether or not our galaxy contains low-mass dark matter subhalos.

Inside the Gigantic Universe

Physicist Jim Al-Khalili explores the incomprehensible scale of the universe. A cosmic journey into the laws of gravity, relativity, and the formation of supergalaxies. Discover how the largest structures shape our understanding of the cosmos itself.

Director: Tim Usborne.
Writers: Jim Al-Khalili, Tim Usborne.
Stars: Prof. Jim Al-Khalili (Physicist, Presenter)
Genre: Science Documentary, Physics, Cosmology.
Country: United Kingdom.
Language: English Also Known As: Secrets of Size: Going Big (BBC)
Release Date: 2022
Filming Location: United Kingdom / Various International Locations.

Synopsis:

In this second episode of the fascinating series Secrets of Size, Professor Jim Al-Khalili takes us on a cosmic journey into the immensity, exploring the largest scale of the universe.

We leave behind the quantum realm to focus on the forces that govern the largest structures: gravity and relativity. Al-Khalili explains how these laws shape the existence of galaxies, galaxy clusters, and the immense supergalaxies.

The episode reveals the incomprehensible scale of the cosmos, where time and space are distorted, and how the study of these giants allows us to understand the origin, evolution, and perhaps the ultimate destiny of the universe itself.

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Quantum entanglement and the illusion of time, in 79 minutes

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Up next.
Brian Cox: The quantum roots of reality | Full Interview ► • Brian Cox: The quantum roots of reality |…

Time feels obvious, but physics tells a stranger story about its existence: Theoretical physicist Jim Al-Khalili explores why our sense of time may be incredibly misleading, including the idea that past, present, and future might all exist at once.

0:00 Chapter 1: Does time flow?
2:42 Why Time Feels Faster as We Age.
3:56 Time and Change in Philosophy and Physics.
5:28 Einstein and the End of Absolute Time.
6:19 Time in the Equations of Physics.
7:50 Chapter 2: How do we reconcile quantum field theory with the general theory of relativity?
12:10 Evidence for Time Dilation: Muons.
14:29 Gravity Slows Time: General Relativity.
19:22 Space-Time and the Block Universe.
21:55 Does Time Really Exist?
26:33 The Debate: Eternalism vs Presentism.
34:12 Chapter 3: Is There a “Now”?
40:40 Chapter 4: Why Does Thermodynamics Have a Direction in Time?
49:38 Quantum Entanglement and the Direction of Time.
55:10 Did Time Begin at the Big Bang?
45:00 Will Time End?
1:05:40 Chapter 5: Is Time Travel Possible?

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Dark matter experiment reaches ultracold milestone

An international collaboration, including Northwestern University, has reached a critical milestone in the search for dark matter, the mysterious substance that makes up about 85% of all matter in the universe. Located two kilometers below ground in Canada, the Super Cryogenic Dark Matter Search (SuperCDMS) at SNOLAB has cooled to its operating temperature, the collaboration announced on March 17.

Just thousandths of a degree above absolute zero, the cryogenic experiment is about 100 times colder than the temperature of deep space. This extreme cold enables scientists to eliminate thermal noise from vibrating atoms, potentially isolating dark matter’s incredibly tiny signals.

With this milestone, the project transitions from building the experiment to preparing for the search. Researchers can now turn on the dark matter detectors, whose superconducting sensors only function when cooled to extremely low temperatures. If the equipment operates correctly, it should achieve the highest level of sensitivity yet for detecting low-mass particles, which have about half the mass of a single proton.

Searching for the Nature of Dark Matter

Dark matter makes up most of the matter in our Universe, yet its true nature remains one of the greatest mysteries in modern science. In this webinar, leading Cambridge researchers will explore how we’re uncovering the invisible.

Chaired by Professor Anthony Challinor, Director of the Kavli Institute for Cosmology, this webinar brings together three Cambridge researchers on the front line of dark matter research:

Professor Ben Allanach (Department of Applied Mathematics and Theoretical Physics)
Professor Hiranya Peiris (Institute of Astronomy and Kavli Institute for Cosmology)
Dr Harry Cliff (Cavendish Laboratory, Department of Physics)

Astronomers May Have Seen Colliding Black Holes Trigger a Blaze of Light

A brief blaze of gamma and X-ray light that lit up Earth telescopes in November 2024 may have come from an unexpected source.

Just a few seconds earlier, from the same tiny corner of the sky, LIGO-Virgo-KAGRA had detected the telltale gravitational wave signal of two black holes colliding. These massive events are some of the most extreme in the Universe; even so, they’re not generally expected to produce detectable light.

A team led by astronomer Shu-Rui Zhang of the University of Science and Technology of China has linked the extraordinary detection to an even more extraordinary set of possible circumstances: the collision, the researchers believe, may have taken place in the enormous, roiling disk of dust and gas surrounding a third, supermassive black hole – the host galaxy’s active galactic nucleus (AGN).

Could a recently detected ultra-high-energy neutrino be linked to new physics?

Neutrinos are extremely lightweight and electrically neutral particles that rarely interact with ordinary matter. Due to these rare interactions, neutrinos can travel across space almost entirely unaffected, carrying information about highly energetic cosmological events, such as exploding stars or supermassive black holes.

The KM3NeT neutrino telescope, an observatory located at the bottom of the Mediterranean Sea, recently detected the presence of a neutrino carrying extremely high energy, above 100 PeV (peta-electronvolts). This is one of the most energetic neutrinos observed to date.

Theoretical predictions suggested that another large-scale neutrino detector, namely the IceCube detector, would also observe similar high-energy neutrino events. However, this did not happen, which might potentially hint at some new physics, such as a new type of neutrinos or non-standard interactions, that are not included in the standard model of physics.

Globular cluster NGC 5824 is embedded in a dark matter halo, study suggests

Using data from the Magellan Clay telescope and the Canada-France-Hawaii Telescope (CFHT), astronomers have investigated a galactic globular cluster known as NGC 5824. Results of the new study, available in a paper published March 5 on the arXiv pre-print server, suggest that the cluster is embedded in a dark matter halo.

NGC 5,824 is an old globular cluster (GC) located some 104,000 light years away in the Milky Way’s outer halo. It has a mass of about 1 million solar masses, an age of 12.8 billion years and is the second brightest globular cluster of the outer halo clusters. NGC 5,824 is known to have a diffuse stellar envelope that extends beyond its tidal radius and symmetrically surrounds the cluster.

Given that the origin of the stars in this envelope and whether they remain gravitationally bound to the cluster center is still unclear, a team of astronomers led by Paula B. Díaz of the University of Chile decided to investigate NGC 5,824 by analyzing the data from the survey of the Milky Way outer halo satellites, based on the images acquired by CFHT and the Magellan Clay telescope. The study was complemented by data from ESA’s Gaia satellite.

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