Relativity 4 Engineers Weblog

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Clock Tick Rates

Do moving clocks really tick slower? It is hard to tell, because relative to what are they "moving"? If there are two clocks in relative motion, which one is moving? Read more about the issues involved.

Loedel diagrams

Loedel diagrams are special cases of the Minkowski spacetime diagram, very easy to use when only two inertial frames are considered. It is an excellent tool for teaching Special Relativity.

Twin paradox graphical solution

The twin paradox graphical solution is the ultmate way of comprehending the subtleties of Special Relativity. Read and discuss this solution on the Blog.

Space War Puzzle

The Space War Puzzle explores the perplexities of simultaneity and relative positions at high-speed flight.

Apollo Lunar Laser Ranging

Apollo lunar laser ranging test aims for sub-millimeter accuracy.

LED Puzzle

The LED puzzle makes one think hard about simultaneity in Special Relativity. The outcome looks paradoxical, but it is not.

Relativistic Orbits Can be Stunning

Relativistic orbits can be stunningly beautiful. Have a look it this one. It was produced using the equations in Relativity 4 Engineers

GLAST Off!

June 11, 2008: Today, NASA's Gamma-ray Large Area Space Telescope (GLAST for short) left Earth onboard a Delta II rocket. "The entire GLAST Team is elated," reported program manager Kevin Grady of NASA's Goddard Space Flight Center shortly after the rocket's liftoff from Cape Canaveral. "The observatory is now on-orbit and all systems continue to operate as planned." (Science@NASA)

Whereto Gravity Probe B?

A senior review of NASA's astrophysics missions has concluded that a satellite that is trying to measure gravitational effects predicted by Einstein's theory of general relativity should receive no additional funding after this September. (Physicsworld.com)

What now?

Cosmic Censorship

Read how nature attempts to hide the bizarre "naked singularities" that are seemingly possible under certain conditions. (ars technica)

Largest-Ever Dark Matter Structures Discovered

To glimpse the unseen structures, the team of French and Canadian scientists "X-rayed" the dark matter, an invisible web that may make up more than 80 per cent of the mass of the universe. OK, it wasn't X-rays, but rather gravitational lensing ... [University of British Columbia]

Double Einstein Ring

A double Einstein Ring image was captured by the Hubble Space Telescope, and shows a central galaxy surrounding by an almost complete ring, with another fainter ring around that. Like a bull's-eye... [Universe Today]

Massive gas cloud speeding to collision with Milky Way

A giant cloud of hydrogen gas is speeding toward a collision with our Milky Way Galaxy, and when it hits -- in less than 40 million years -- it may set off a spectacular burst of stellar fireworks. (Spaceflight Now)

Private Moon Race on the Way?

Since the competition was announced September 13, well over 300 registration requests have come in from all over the world, said Peter Diamandis, Chairman and Chief Executive Officer of the X Prize Foundation. (Livescience.com)

Quasar Wind

Quasar wind is one of the hot topics discussed in cosmology today. Find out more about these strange beasts and their atmospheres.

Fantastic Skies of Orphan Stars

What a view! It's late summer, after dark, and you're flat on your back in a sleeping bag watching the camp fire's last embers drift up to the heavens. Overhead a magnificent band of stars divides the night - it's the Milky Way. Now, imagine that scene doubled in brightness and beauty. [NASA]

Stardust or Quasardust?

We may be more than what Carl Sagan said (stardust); we may also be 'quasardust'. (Globalspec CR4)

Dark Energy not Needed?

"It has been shown that the nonlocal nature of quantum loop gravity can create a very long apparent delay between a critical phase transition and its measurable effect. In this case, the influence of the transition from a light-dominated universe to a matter-dominated universe, which occurred a very long time ago, shows up as the cause of the recent new period of acceleration that we have labeled dark energy." (ARSTechnica)

Tachyon Puzzle

In relativity theory, tachyons are hypothetical particles that can only move faster than light (FTL) in every inertial frame of reference. It is also said that such FTL particles can arrive 'there' before they leave 'here' and can hence send information back in time, violating cause-before-effect (causality) principles. Read more, with comments, on the Relativity and Cosmology Blog.

Galactic Building Blocks Spotted

Astronomers have found nine of the faintest, tiniest and most compact galaxies ever seen.

The little objects are hundreds to thousands of times smaller and vastly younger than our Milky Way, lending support to a "building block" theory in which hundreds of the tiny galaxies merge together and form larger bodies of stars. (Space.com)

How Orbits Work

How orbits work - demystified - relativistic and Newton's. Download pdf.

Huge Hole in Universe Observed

This big void is nearly a billion light-years across, mostly devoid of stars, gas and other normal matter, and it's also strangely empty of the mysterious "dark matter" that permeates the cosmos. Other space voids have been found before, but nothing on this scale. [Space.com]

Cosmic Energy

According to present standard cosmological theory, an 'inflationary epoch' imparted an enormous 'kinetic energy' of expansion upon the embryo universe. A brief look at the order of magnitude of this energy.

Quantum Cosmology

Quantum cosmology deals with the universe when it was incredibly dense, just after the big bang. A brief overview of what it is about.

Quantum Gravity

Quantum gravity is the cutting edge of gravitation research. A brief summary of the two leading contenders in the 'race'.

Biggest Recorded Collision in Cosmos

The orbiting X-ray telescopes XMM-Newton and Chandra have caught a pair of galaxy clusters merging into a giant cluster. This is a collision on a super-galactic scale.

The Origin of Inertia

Is the origin of inertia in Mach's principle or in temporal stresses? Was Einstein right about it?

What is Cosmology?

A brief answer to the question "what is cosmology?" It introduces non-technical people to physical cosmology, the scientific study of the Universe at large

What is Gravity?

Updated, non-technical answer to the question: what is gravity? Deals with the evolution of classical gravity theory by Kepler, Newton and Einstein. (Relativity 4 Engineers)

Is Special Relativity Comprehensible?

One of the problems with special relativity is the fact that it essentially operates in "empty space", where there are no objects or matter that could serve as fixed reference points. Motion is relative, so does it matter? It does if you accelerate a clock to high speed, leave it to travel freely for some time and then compare it's time with your own clock. (Globalspec CR4)

Most Distant Black Hole Discovered

The most distant black hole found so far is nearly 13 billion light-years from Earth, astronomers announced on June 7, 2007. (Space.com)

The shape of the Universe

Our observable universe is very close to a sphere with us at the center, but that is only because we have a spherical horizon around us. The horizon is roughly at the distance that light could have traveled since the birth of our Universe. (Globalspec CR4)

Bell's Spaceship Paradox

Another "controversial paradox", this time about the interpretation of accelerating systems in Einstein's special relativity. Read the article and comments and write comments on the Globalspec CR4 Blog.

The Twin Paradox

This old gem of a "paradox" is still making people uneasy. Here is a two-part 'engineering view' of the solution to the twin paradox.

Broken Einstein Rings

When thing do not line up perfectly, Einstein's rings are broken in several possible ways. Read about it and the relatively simple math that underpins this phenomenon. (CR4 Globalspec.com)

Black Hole Accretion Disk Sized

NASA's Chandra X-ray Observatory has observed a remarkable eclipse of a supermassive black hole, allowing a disk of hot matter swirling around the hole to be measured for the first time. (NASA)

Time Travel a Dream?

While time travel has long been achievable with the artistic license of novel-writing or movie-making -- one of the earliest time travel stories, Samuel Madden's "Memoirs of the Twentieth Century", was written as far back as 1733 -- the idea of time travel as a practical reality has generally been dismissed as impossible.

Over the last 25 years, however, with some great advances in the field of quantum physics, an increasing number of serious scientific thinkers have come round to the view that not only is time travel theoretically feasible but also, in some circumstances, practically so as well. (CCN)

Origins of the universe

Stephen Hawking, the Lucasian professor of mathematics at Cambridge University delivered the J. Robert Oppenheimer Lecture in Physics on March 13, 2007. It is a must read! (UC Berkeley News)

Center of Milky Way a Colossal Particle Accelerator?

The black hole at the center of our Milky Way could be working like a cosmic particle accelerator, revving up protons that smash at incredible speeds into lower energy protons and creating high-energy gamma rays. (Spaceflight Now)

Spinning Binary Black Holes Problem Solved!

Einstein would be proud. One hundred years after the great scientist and humanist challenged conventional wisdom and published his famous Special Theory of Relativity (1905), a team of modern-day physics researchers at The University of Texas at Brownsville (UTB) and the Rochester Institute of Technology have finally solved the Einstein field equations for coalescing black hole binaries on supercomputers. (TACC)

Storing light here -- and retrieving it there

Physicists in the US have been able to imprint a coherent pulse of light on a collection of ultracold atoms -- and then retrieve the same light pulse from a second set of atoms that is some distance away. The experiment proves that macroscopic particles can be quantum mechanically indistinguishable even though they are physically separate. The work was carried out using Bose-Einstein condensates (BECs) -- atoms cooled to such low temperatures that they are all in the same quantum state (Nature 445 605).

Black Holes - How They Work

A engineer's introduction to black holes, with links to more technical stuff - and you don't need to be an engineer to follow the material! (Globalspec CR4)

What is Gravity?

No one knows what this mysterious force really is, but Einstein came closest in describing it (so far). This short article gives a view into "Einstein's gravity".

What is Relativity?

Here's a new non-technical article, starting with Einstein's answer and then going one step further...

Spinning Black Hole Pushes Limit

A Center for Astrophysics-led team has measured a black hole spinning so rapidly that it pushes the predicted speed limit for black hole rotation. It is turning more than 950 times per second. (Space Daily)

The History of Dark Energy

Scientists now have evidence that dark energy has been around for most of the universe's history. (Space.com)

The Einstein-de Sitter Model of the Universe

The Einstein-de Sitter model of the expanding universe - introduction and pdf download

PPN Formalism of Gravitation Theory

The Parameterized Post-Newtonian Formalism - PPN Formalism for short. Download pdf.

Tests of Relativity - putting Einstein to the test

Einstein was right - so far - says tests of relativity after almost a century

Gravitational Waves

Ripples in space-time equals gravitational waves, propagating at c. Download pdf.