Physics Archives

December 19, 2023December 21, 2023 by Paul M. Sutter

Why String Theory Requires Extra Dimensions

String theory found its origins in an attempt to understand the nascent experiments revealing the strong nuclear force. Eventually another theory, one based on particles called quarks and force carriers called gluons, would supplant it, but in the deep mathematical bones of the young string theory physicists would find curious structures, half-glimpsed ghosts, that would point to something more. Something deeper.

December 16, 2023December 16, 2023 by Matt Williams

Scientists are Recommending IceCube Should be Eight Times Bigger

This image shows a visual representation of one of the highest-energy neutrino detections superimposed on a view of the IceCube Lab at the South Pole. Credit: IceCube Collaboration

The IceCube Neutrino Observatory, operated by the University of Wisconsin-Madison (UW-M), located at the Amundsen–Scott South Pole Station in Antarctica, is one of the most ambitious neutrino observatories in the world. Behind this observatory is the IceCube Collaboration, an international group of 300 physicists from 59 institutions in 14 countries. Relying on a cubic kilometer of ice to shield from external interference, this observatory is dedicated to the search for neutrinos. These nearly massless subatomic particles are among the most abundant in the Universe and constantly pass through normal matter.

By studying these particles, scientists hope to gain insight into some of the most violent astrophysical sources – such as supernovae, gamma-ray bursts, merging black holes and neutron stars, etc. The group of scientists tasked with advising the U.S. government on particle physics research is known as the Particle Physics Project Prioritization Panel (P5). In a recent draft report, “Pathways to Innovation and Discovery in Particle Physics,” the P5 team recommended a planned expansion of IceCube. This recommendation is one of several that define the future of astrophysics and particle physics research.

December 6, 2023December 9, 2023 by Matt Williams

Communicating With a Relativistic Spacecraft Gets Pretty Weird

Artistic rendition of an interstellar spacecraft traveling near the speed of light. Credit: Made with ChatGPT

Someday, in the not-too-distant future, humans may send robotic probes to explore nearby star systems. These robot explorers will likely take the form of lightsails and wafercraft (a la Breakthrough Starshot) that will rely on directed energy (lasers) to accelerate to relativistic speeds – aka. a fraction of the speed of light. With that kind of velocity, lightsails and wafercraft could make the journey across interstellar space in a matter of decades instead of centuries (or longer!) Given time, these missions could serve as pathfinders for more ambitious exploration programs involving astronauts.

Of course, any talk of interstellar travel must consider the massive technical challenges this entails. In a recent paper, a team of engineers and astrophysicists considered the effects that relativistic space travel will have on communications. Their results showed that during the cruise phase of the mission (where a spacecraft is traveling close to the speed of light), communications become problematic for one-way and two-way transmissions. This will pose significant challenges for crewed missions but will leave robotic missions largely unaffected.

November 28, 2023November 28, 2023 by Evan Gough

The Second Most Energetic Cosmic Ray Ever Found

An example of a cosmic-ray extensive air shower recorded by the Subaru Telescope. The highlighted tracks, which are mostly aligned in similar directions, show the shower particles induced from a high-energy cosmic ray. Credit: NAOJ/Hyper Suprime-Cam (HSC) Collaboration

“Oh My God,” someone must have said in 1991 when researchers detected the most energetic cosmic ray ever to strike Earth. Those three words were adopted as the name for the phenomenon: the Oh-My-God particle. Where did it come from?

November 13, 2023November 9, 2023 by Paul M. Sutter

Why Even Einstein Couldn’t Unite Physics

Einstein Lecturing — Albert Einstein during a lecture in Vienna in 1921. Credit: National Library of Austria/F Schmutzer/Public Domain

Near the end of his life Einstein worked tirelessly to find a way to unite electromagnetism with gravity. He could not, and never did, the notes scattered on his desk scrawled with fruitless probes and useless hypotheticals. Indeed, Einstein passed without even understanding why the two forces could not be united.

November 12, 2023November 9, 2023 by Paul M. Sutter

How Einstein Unlocked the Quantum Universe and Created the Photon

This all-sky Fermi view includes only sources with energies greater than 10 GeV. From some of these sources, Fermi's LAT detects only one gamma-ray photon every four months. Brighter colors indicate brighter gamma-ray sources. Credit: NASA/DOE/Fermi LAT Collaboration

It started with a simple experiment that was all the rage in the early 20^th century. And as is usually the case, simple experiments often go on to change the world, leading Einstein himself to open the revolutionary door to the quantum world.

November 11, 2023November 9, 2023 by Paul M. Sutter

How to Think About a Four-Dimensional Universe

Hubble image of SDSSJ0146-0929, a galaxy cluster that is massive enough to severely distort the spacetime around it. There's the mass of the visible stars and gas, but there's also a hidden amount of dark matter that adds to the cluster's mass. Credit: ESA/Hubble & NASA; Acknowledgment: Judy Schmidt

In Einstein’s famous theory of relativity the concepts of immutable space and time aren’t just put aside, they’re explicitly and emphatically rejected. Space and time are now woven into a coexisting fabric. That is to say, we truly live in a four-dimensional universe. Space and time alone cease to exist; only the union of those dimensions remains.

November 10, 2023November 9, 2023 by Paul M. Sutter

Is Anything Absolute with Relativity?

Researchers crunched Einstein's theory of general relativity on the Columbia supercomputer at the NASA Ames Research Center to create a three-dimensional simulation of merging black holes. Image Credit: Henze, NASA

The theory of relativity is at once simple and elegant but also maddeningly nonintuitive. There’s no need to get into the full guts and glory of that theory here, but there is one feature of Einstein’s work that takes center stage, and would eventually lead him into a complete reshaping of Newton’s gravity, altering our very conceptions of the fabric of the universe.

November 9, 2023November 9, 2023 by Paul M. Sutter

How Einstein’s Daydream of Light Created Relativity

Lasers are used to squeeze atoms and entangle them. Credit: MIT

Einstein’s fascination with light, considered quirky at the time, would lead him down the path to a brand new theory of physics.

October 24, 2023October 24, 2023 by Alan Boyle

‘Her Space, Her Time’ Reveals the Hidden Figures of Physics

Sepia-tone photos of Leavitt, Payne-Gaposchkin, Rubin and Alexander — These are just four of the women physicists profiled in "Her Space, Her Time": Henrietta Swan Leavitt, Cecilia Payne-Gaposchkin, Vera Rubin and Claudia Alexander. (Credits: Wikimedia; Smithsonian Institution; Rubin photo by Mark Godfrey, courtesy of AIP Emilio Segre Visual Archives; NASA)

Quick: Name a woman scientist.

Chances are the name you came up with is Marie Curie, the physicist and chemist who won two Nobel Prizes more than a century ago for the discoveries she and her husband Pierre made about radioactivity.

But who else? In a new book titled “Her Space, Her Time,” quantum physicist Shohini Ghose explains why women astronomers and physicists have been mostly invisible in the past — and profiles 20 researchers who lost out on what should have been Nobel-level fame.

“This issue around having low representation of women in physics is something that’s common all around the world,” Ghose says in the latest episode of the Fiction Science podcast. “And I’ve certainly faced it in my own experiences as a physicist growing up. I really didn’t know of any woman physicist apart from Marie Curie.”