Relativity
esiegel | January 13, 2015When we talk about dimensions, we're used to thinking of three: something like length, width and depth, or x, y and z. But there's a fourth dimension as well that's of paramount importance for our Universe, otherwise everything would simply be static: time.
Image credit: Fair Use image obtained by Wikimedia Commons user DASHBot.
Our motion through time as well as space is what allows things to be different from one moment to the next. Although relativity (and Einstein) are what we commonly associate with these ideas, they predate him in both fiction (above) and science (below), such as…
esiegel | November 1, 2014“I think one of the coolest things you can do is disappear for a while, because it gives you the chance to re-emerge.” -Josh Homme
The Big Bang -- and General Relativity in general -- teaches us that in an expanding Universe, it's the fabric of space itself that evolves over time. One of the consequences of this is a bit puzzling: that since the Universe was denser in the past, it must have been hotter in the past as well.
Image credit: NASA / GSFC.
But if each individual photon has redshifted to longer wavelengths, and the energy of every photon is inversely proportional to that…
esiegel | September 30, 2014When it comes to physics, there sure are some strange theories -- and even stranger phenomena -- out there. The notion that particles don't have fixed, intrinsic properties that are simultaneously measurable can only be described as weird, and the fact that you can add as much energy as you want to a particle but it will never accelerate to beyond a particular speed is certainly counterintuitive. Yet one theory has them all beat.
Image credit: John D. Norton, via http://www.pitt.edu/~jdnorton/teaching/HPS_0410/chapters/Special_relati….
For ninety-nine years, now, General Relativity has…
esiegel | September 23, 2014When it comes to Einstein, the first thought that comes to people's mind is usually relativity -- either special or general -- or perhaps his famous E = mc^2. (Except for Anupam Garg; my old classical mechanics professor used to joke that Einstein's greatest contribution to physics was his shortened summation notation.) But Einstein's legacy goes much deeper than any of that.
Image credit: Wikimedia commons users Markus Poessel and Pbroks13.
You see, one of the greatest things that Einstein pioneered was the Gedankenexperiment, or the idea of performing an experiment in your mind. These…
esiegel | May 29, 2014“Oh leave the Wise our measures to collate. One thing at least is certain, light has weight. One thing is certain and the rest debate. Light rays, when near the Sun, do not go straight.” -Arthur Eddington
It might seem like General Relativity has been around forever, but it's been less than a century since it was released and confirmed. In fact, today marks the 95th anniversary of the solar eclipse that changed our view of the Universe!
Actual negative and positive photographic plates from the 1919 Eddington Expedition, via http://www.sciencebuzz.org/buzz-tags/eddington-expedition.
The…
esiegel | May 22, 2014“These neutrino observations are so exciting and significant that I think we’re about to see the birth of an entirely new branch of astronomy: neutrino astronomy.” -John Bahcall
From the Hubble expansion of the Universe to isotropy and homogeneity to the light elements to the leftover radiation glow to the formation of large-scale structure in the Universe, the Big Bang is by far the most successful scientific description of the Universe of all-time.
Image credit: Illustris Simulation, M. Vogelsberger, S. Genel, V. Springel, P. Torrey, D. Sijacki, D. Xu, G. Snyder, S. Bird, D. Nelson, L.…
esiegel | May 13, 2014“For my part I know nothing with any certainty, but the sight of the stars makes me dream.” -Vincent Van Gogh
Ever since the BICEP2 team reported their findings -- and evidence for B-mode polarization of the cosmic microwave background indicating gravitational waves from inflation -- the physics world has never been the same.
Images credit: Seljak & Zaldarriaga (L), Wayne Hu (R), viahttp://cosmology.berkeley.edu/~yuki/CMBpol/CMBpol.htm.
Recently, there have been rumors that perhaps this B-mode signal is due to the Milky Way, and not due to inflation after all. If this does turn out to…
esiegel | April 17, 2014“Other than the laws of physics, rules have never really worked out for me.” -Craig Ferguson
When you think about the Standard Model of particle physics, you very likely think about all the matter, energy, particles, antiparticles, forces and interactions of the Universe. And you might legitimately worry that this is all there is.
Image credit: Fermilab, modified by me.
Never fear; it can't be! The Standard Model may be wonderful for what it does predict, but we know with absolute certainty that it can't be everything.
Image credit:the BICEP2 collaboration, via http://www.cfa.harvard.edu/…
esiegel | March 21, 2014“The conclusions, the bizarre conclusions, emerge as though with the greatest of ease: the reasoning is unbreakable. It looks as though he had reached the conclusions by pure thought, unaided, without listening to the opinions of others. To a surprisingly large extent, that is precisely what he had done.” -C.P. Snow, on Einstein’s 1905 work
In 1887, two scientists set out to measure how the speed of light changed with the Earth’s motion. What they didn’t find wound up changing the world.
Image credit: Albert Abraham Michelson, 1881.
Today's Ask Ethan is all about the most famous failed…
esiegel | March 20, 2014“All our sweetest hours fly the fastest.” -Virgil
The speed of light in a vacuum is the limit for massless particles, but massive ones are limited even further! Have you ever wondered about that?
Image credit: ICEPP via https://www.icepp.s.u-tokyo.ac.jp/history/lep-e.html (L); LEP / CERN, via http://www.madrimasd.org/ (R).
We can get particles in accelerators up to 99.9999999988% the speed of light, and the Universe makes ones that are even faster! But despite all of this, there's a limit, and that limit is more restrictive than the speed of light in a vacuum!
Image credit: Simon Swordy (…
esiegel | February 21, 2014“If you put yourself in a position where you have to stretch outside your comfort zone, then you are forced to expand your consciousness.” -Les Brown
On the one hand, you've got gravitation, the most powerful force in the Universe, trying to attract all the matter in it together. If it had its way, not only would everything eventually merge together, but the Universe itself would recollapse!
Image credit: Eugenio Bianchi, Carlo Rovelli & Rocky Kolb, modifications by me.
But on the other hand, the Universe is not only expanding, but that expansion is accelerating, thanks to the presence…
esiegel | February 14, 2014"For the wise man looks into space and he knows there is no limited dimensions." -Lao Tzu
You know the deal: it's the end of the week, so it's time for another Ask Ethan! You've continued to send in your questions-and-suggestions, much to my delight, and I'm pleased to tell you that this week's question comes from Peter Tibbles. Peter asks about obtaining information from beyond where Einstein's theory of relativity allows us to see:
Because of the expansion of the universe there is an event horizon beyond which we can know nothing. There’s been one instance of intelligent life evolved (us);…
esiegel | January 3, 2014"The world owes you nothing. It was here first." -Mark Twain
When you think about where all of this came from -- back to the beginning of the Universe -- there's a good chance it makes you a little uncomfortable. For this week's Ask Ethan, our one remaining column here on ScienceBlogs, our reader vvv asks a question that quite possibly many of you have wondered:
Why didn't the universe collapse into a black hole right "at the moment of the big bang?"
And quite honestly, I've wondered a fair bit about this myself. Here's why.
Image credit: Kerry-Ann Lecky Hepburn (Weather and Sky Photography…
esiegel | December 27, 2013"Never waste your time trying to explain who you are to people who are committed to misunderstanding you." -Dream Hampton
Perhaps no word in the English language generates as much misunderstanding as the word theory. In scientific circles, this word has a very specific meaning that's different from everyday use, and -- as a theoretical astrophysicist myself -- I feel it's my duty to help explain exactly what we mean when we use it. In this week’s Ask Ethan column, I'm pleased to pull out of our question/suggestion box the question of Ripley, who asks:
I often see that because there is no "100…
esiegel | December 6, 2013"The results of my observation are best explained by the assumption that a radiation of very great penetrating power enters our atmosphere from above." -Victor Hess
You might think of the largest and most powerful particle accelerators in the world -- places like SLAC, Fermilab and the Large Hadron Collider -- as the source of the highest energies we'll ever see. But everything we've ever done hear on Earth has absolutely nothing on the natural Universe itself! For this week's Ask Ethan, let's take a look at the simple question of our reader David Hurn, who asks:
Ever since I was a young…
esiegel | December 5, 2013"Some say the world will end in fire,
Some say in ice.
From what I've tasted of desire
I hold with those who favor fire.
But if it had to perish twice,
I think I know enough of hate
To say that for destruction ice
Is also great
And would suffice." -Robert Frost
Depending on where you are in the world right now, you might really be feeling the effects of the emerging winter, as cold snaps, freezes and snowstorms take hold across the northern hemisphere.
Image credit: NASA's Scientific Visualization Studio, Goddard Space Flight Center.
But we can all be pretty sure that this is temporary,…
esiegel | November 22, 2013“Light thinks it travels faster than anything but it is wrong. No matter how fast light travels, it finds the darkness has always got there first, and is waiting for it.” -Terry Pratchett
It’s the end of the week once again, and so let's have a go at another Ask Ethan! Perhaps inspired by a great giveaway, there have been so many great questions pouring in (and you can submit yours here for four more chances to win), but this week’s comes from our reader and winner Brad (you owe me your email address, Brad), who asks,
When an object is quoted as being 13.8 billion light years away is that…
esiegel | November 15, 2013"I wouldn't know a spacetime continuum or a warp core breach if they got into bed with me." -Patrick Stewart
It's the end of the week once again, and so it's time for another Ask Ethan segment! There have been scores of good questions to choose from that were submitted this month alone (and you can submit yours here), but this week's comes from our reader garbulky, who asks:
Why does gravity decrease the further away you are from the object? I've read that it does decrease with distance squared but not why it does this.
This question seems so simple, and yet the answer -- to the limits of our…
esiegel | November 9, 2013"One of the most tragic things I know about human nature is that all of us tend to put off living. We are all dreaming of some magical rose garden over the horizon instead of enjoying the roses that are blooming outside our windows today." -Dale Carnegie
Our new Ask Ethan segment has been really popular, and the questions and suggestions keep pouring in. It's your Universe too, and if there's something you want to know about it, you should ask! (So keep it up!) This week's question is one of the biggest of them all, and it comes courtesy of John L. Ferri, who asks,
I have a difficult time…
esiegel | October 11, 2013"If you look for truth, you may find comfort in the end; if you look for comfort you will not get either comfort or truth only soft soap and wishful thinking to begin, and in the end, despair." -C. S. Lewis
And yet, when you search for the truth, you often find answers that butt up against your sensibilities, your preconceptions, and even your very notions of common sense. Such is the case in this week's Ask Ethan, where longtime reader and commenter MandoZink asks:
I have a question that has perplexed me for most of my life. Recently I sought out and re-read more expert explanations of the…