gravity
esiegel | July 26, 2011"Birth and death; we all move between these two unknowns." -Bryant H. McGill
One of the most remarkable consequences of the Big Bang is that the Universe as we know it -- full of planets, stars, galaxies and life -- hasn't been around forever! Because the Universe is expanding and cooling, it was hotter, denser, and more compact in the past.
Image credit: SciencePhotoLibrary.
But these things that fill the Universe today weren't there in the very early stages of the Universe; they took time.
Gravity needed many millions of years to collapse these slightly overdense regions to a point where…
esiegel | July 12, 2011"Sometimes I don't want to see the puppeteers,
sometimes I just want to see the magic therein,
and sometimes I just want to pry open the atoms
and know why they spin." -Glen Sutton
But it isn't just the atoms -- the minuscule building blocks of matter -- that spin. It's also the individual galaxies, collections of some mind-boggling number (like 1068) of atoms, that spin.
Image credit: Jean-Charles Cuillandre, Giovanni Anselmi and the CFHT.
Messier 95, above, is just one such example. But how did these galaxies get to be this way?
To answer this question, we have to go all the way back to…
esiegel | June 3, 2011"It is no good getting furious if you get stuck. What I do is keep thinking about the problem but work on something else. Sometimes it is years before I see the way forward. In the case of information loss and black holes, it was 29 years." -Stephen Hawking
When we look out at the Universe, you know what it is that we see.
Image credit: Misti Mountain Observatory.
Light! Light from stars, galaxies, clusters, etc., covering all the different wavelengths you can measure.
But there weren't always stars, galaxies, and clusters in the Universe. When the Universe was first "born," in fact, the…
esiegel | May 20, 2011"We all need to look into the dark side of our nature - that's where the energy is, the passion. People are afraid of that because it holds pieces of us we're busy denying." -Sue Grafton
No, not the dark side of our nature, just the dark side of nature! Because if all our Universe were made out of were atoms and photons, we wouldn't get a Universe that looks like ours.
What do I mean? Let's take a look.
Image credit: MPA Garching and Volker Springel.
The Universe starts off as a very smooth place, where regions that are denser or less dense than average are only something like 0.003% away…
esiegel | May 16, 2011Some 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
Sure, if all we're talking about is the Earth, that one's a no-brainer. It's fire.
Our Sun, very slowly, is burning up its Hydrogen fuel into Helium, through the process of nuclear fusion. But over the course of billions of years, it starts to burn its remaining fuel at an ever increasing rate. Over the next billion or two years, the…
esiegel | May 6, 2011"God does not play dice with the Universe." -Einstein
"Einstein, don't tell God what to do." -Neils Bohr (disputed, but awesome)
Einstein, the brilliant mind behind general relativity and the concept of "spacetime," is making the news again this week. As you all know, gravity isn't some mysterious invisible force traveling across space, it comes about because energy itself -- most commonly in the form of mass -- distorts the very fabric of space.
Image credit: GNU user Johnstone and NASA's Galileo spacecraft.
Of course, wrapping your head around this can prove quite difficult. Space, as we…
esiegel | May 4, 2011"You still don't get it, do you? He'll find her! That's what he does! That's ALL he does! You can't stop him!" -Kyle Reese, the Terminator
Now that we've all survived Judgment Day, we can stop looking for ways to stop the Terminators, and go back to the search for dark matter. Let's back up a bit, though, and take a look at normal matter first.
As you well know, normal matter here on Earth is always subjected to the force of gravity. You throw something up into the air, and the Earth's gravity always works to pull it back down. In general, something moving under only the influence of the…
esiegel | April 20, 2011"You may hate gravity, but gravity doesn't care." -Clayton Christensen
What's the deal with gravity, dark matter, and this whole "lensing" business anyway? You've probably heard that energy -- most commonly mass -- bends light. And perhaps you've seen an image or two like this one to illustrate that.
Image credit: ESA, NASA, J.-P. Kneib and Richard Ellis.
Above is the great galaxy cluster Abell Cluster 2218. But those giant, stretched arcs you see? Those are actually background galaxies that get distorted and magnified by the giant cluster.
As the light leaves its source, the mighty gravity…
esiegel | March 7, 2011"Nothing in life is to be feared, it is only to be understood. Now is the time to understand more, so that we may fear less." -Marie Curie
Were you here last week, when I wrote about MOND and dark matter, and in particular what the supreme failings of MOND are? Apparently, right here on Scienceblogs was a hugely dissenting opinion.
Image credit: Subaru Telescope.
After all, when you look at what we call small-scale structure, from dwarf spheroidal galaxies up to the scales of some very small galaxy clusters, MOND works even better than dark matter does!
So what is dark matter, and why am I…
jhalper | March 6, 2011
Dark matter - that invisible stuff that is supposed to make up some 20% of the Universe - was thought up to explain a puzzling observation. The amount of mass we can see through our telescopes is not enough to keep galaxies from spinning apart. The existence of great quantities of hidden mass would provide the gravitational pull needed to form those galaxies and enable them to rotate in the way that they do.
But not everyone is willing to buy the idea that the Universe is cloaked in "invisible cloth." An alternate theory, first put forward by Weizmann Institute astrophysicist Prof. Moti…
esiegel | March 1, 2011"There's an old saying about those who forget history. I don't remember it, but it's good." -Stephen Colbert
Let me start by telling you a story about an old problem. Take a look at the planet Mercury, one of the five planets (not counting Earth) visible in our night sky to the naked eye.
And I can see some of you at home squinting at your screen, asking why I'm showing you a picture of the Moon right after sunset. Well, Mercury's in that picture, I promise. Let me make it a little easier for you.
No less a naked-eye astronomer than Copernicus had difficulty seeing the planet Mercury, and…
esiegel | January 20, 2011"What do we mean by setting a man free? You cannot free a man who dwells in a desert and is an unfeeling brute. There is no liberty except the liberty of some one making his way towards something. Such a man can be set free if you will teach him the meaning of thirst, and how to trace a path to a well. Only then will he embark upon a course of action that will not be without significance. You could not liberate a stone if there were no law of gravity -- for where will the stone go, once it is quarried?" -Antoine de Saint-Exupery
Gravity, on the largest scales, rules everything in the Universe…
esiegel | January 5, 2011"The size of the universe is no more depressing than the size of a cow." -David Deutsch
But it is bizarre, I'll give you that. The most common scientific question I get asked is how, if the Universe is 13.7 billion years old, and the speed limit of the Universe is the speed of light, why do I say the observable Universe is 93 billion light years across?
In other words, why is this picture of the Universe wrong?
I've tried to answer this before, and so have others, but perhaps it's time for another -- more conceptual -- attempt. This is one of the most mind-boggling things about relativity.…
esiegel | December 30, 2010"There is only one corner of the universe you can be certain of improving, and that's your own self." -Aldous Huxley
Earlier this week, I told you the story of how we went from a Universe that was -- at one time -- almost perfectly smooth, full of tiny, random fluctuations in density,
to the Universe we have today, full of stars, galaxies, and clusters of galaxies all clumped together in a beautiful cosmic web of structure.
But there was one picture I showed that generated a lot of questions. I put up an image showing what the Universe was made out of today (when we have this great cosmic…
esiegel | December 28, 2010You may find yourself living in a shotgun shack
You may find yourself in another part of the world
You may find yourself behind the wheel of a large automobile
You may find yourself in a beautiful house, with a beautiful wife
You may ask yourself: well... how did I get here? -Talking Heads
Yesterday's Astronomy Picture of the Day was this beautiful shot of the nearest 1.5 million (or so) galaxies, as mapped by the 2-Micron All-Sky Survey, with our galaxy shaded in blue.
Now, if you're an astrophysicist, you might ask yourself how these nearby galaxies are distributed. Are they regularly…
esiegel | December 8, 2010"Why it is that of all the billions and billions of strange objects in the Cosmos -- novas, quasars, pulsars, black holes -- you are beyond doubt the strangest?" -Walker Percy
Black holes. You've all heard them before, and you can visualize them pretty easily. How so? Start by thinking about the Earth.
Held together by the immense force of gravity, the Earth is a difficult world to leave.
What exactly do I mean by that?
It takes a tremendous amount of energy to get off of the planet Earth. If you were at the surface of the Earth, you'd have to be moving at around 40,000 km/hr (or 25,000 mi/…
esiegel | October 20, 2010"The laws in this city are clearly racist. All laws are racist. The law of gravity is racist." -Marion Barry
The law of gravity, contrary to what Marion Barry says, is -- perhaps -- the most indiscriminate of all the laws of nature.
What do I mean? Well, you get a large collection of matter and energy together, like in a galaxy, and what does it do? It pulls -- with the entirety of the irresistible force of gravity -- on everything. Give the most massive collections of matter enough time, and they'll pull in everything around them for tens of millions of light years.
And when you do, you'll…
rallain | September 8, 2010Actually, it should be called Happy "Magnitude of the local Earth gravitational field" day. You know, 9.8 N/kg on September 8 (9/8). Get it? Well, the idea was for the physics students and faculty to build some stuff to do outside - projectile motion type stuff. Well, we had the idea a while ago and then kind of forgot about it.
In order to just get something done, I set up the "shoot the falling target" demo. (previously known as shoot the monkey). Here is a quick video demo (seriously - first take too).
What is going on here and what does this have to do with g? Well, it doesn't…
esiegel | August 30, 2010"The whole fabric of the space-time continuum is not merely curved, it is in fact totally bent." -Douglas Adams
As many of you know, if you take a whole bunch of mass, and you've got nothing going on except gravity, it's going to gravitationally collapse. And if atoms, nuclei, pressure, and nuclear reactions don't (or can't) prevent that gravitational collapse from running away, you're going to wind up with a black hole.
But last week, I told you that if you took all the matter in the Universe and shaped it into a cylinder, you'd actually wind up with a huge cylinder of solid matter, as big…
drorzel | August 27, 2010I'm pretty sure I've used this topic before, but not with PollDaddy. And while I really ought to do a ResearchBlogging post today to make it a clean sweep for the week, I just don't have the energy.
So here's a poll: what's your favorite fundamental force?
What's your favorite fundamental force?online surveys
Those of us with corporeal existence should restrict our answers to the low-energy condition of the present material universe, not any of the higher energy unification scales.