The American Museum of Natural History is dedicated to preserving our planet's past. But its new app, which offers turn by turn directions to exhibits, customizable museum tours, and exhibit information, is nothing less than state of the art. More »
One topic which generated a lot of discussion at the Gravity and Cosmology meeting was the void model of the Universe. The basic argument is simple: the dark energy is an ugly addition to our cosmological standard model, with 70% of the energy density of the Universe some mysterious substance with weird properties. From a theoretical perspective, dark energy has the wrong density by many, many orders of magnitude, and worse, we may never be able to study it directly in the laboratory. Now suppose I told you I had a model which explained all of the observations, was based on general relativity, and appealed to no mysterious dark energy component (but still has dark matter, unfortunately). Sounds tempting, right? This is precisely what John Moffat, Chris Clarkson, Antonio Enea Romano, Chul-Moon Yoo, and others were advocating at the workshop (Kenji Tomita has also done a lot of work on this; the model has been around for decades). There’s one important caveat, however. The void model throws out the homogeneity and isotropy assumption. The Universe is now spherically symmetric, with a big hole in the middle. Even worse, we happen to be very, very close to the center of the hole.
As I discussed in a previous post, John Moffat argues that we shouldn’t be any more disturbed by this model than the standard model, because they’re both anti-Copernican: the void model in space, the standard model in time. As I discuss in that post, I’m not sure I completely agree with this. The fine tuning for the average void model is fairly involved. First, the matter density must be carefully set, as a function of radius, to agree with observation of the luminosity-distance relation. Then we have to be set down within roughly 1 Mpc of the center of the spherical void (which is at least a few Gpc on a side). If we were at a random spot in the Universe, there’s a probability of much less than 1 in 10 billion that we’d end up sufficiently close to the center of a void (assuming such voids existed). On the other hand, the standard Lambda CDM model of cosmology requires fine-tuning of the cosmological constant to a tiny, but non-zero number. To some this is unbearably ugly. But, at the end of the day, it’s just one additional, arbitrary number.
All this being said, what’s great about void models is that they aren’t just a philosophical alternative to the standard model. This is physics. There are measurements that can be done to differentiate (and possibly falsify) these models. Stebbins & Caldwell have come up with one particularly interesting approach, exploiting the fact that “random” observers in a void model see a different sky (and hence, a different CMB) from the one we do in our privileged position. It is surprising that a model so radically different from our standard model is still viable (although under pressure). Tests over the next few years are expected to distinguish these models, and we’ll know definitively whether we are at the center of the Universe.
Available only on pre-order up until now, the Nikon thermos joins its biggest rival, the Canon thermos, in the hallowed hall of camera-lens thermoses that are actually up for purchase. Just $23. [100milligrams via NPR via TWBE] More »
From Gizmodo:
This cube may look like hell's version of Jenga, but it's actually an elaborate, 125-piece puzzle. The solution? A single-shot 45-caliber muzzle-loading pistol called the Intimidator. No, seriously. See for yourself.
Read the whole article
Looking for Ground Cable Reels Model GR 75 what the price is
CR4 Admin: Do not disclose your phone number on a public forum.
Hello folks, I'm hoping you can shed some light on a debate in my office over the tariff classification of most of the time measurment devices we see today.
I think this is another example of the customs tariff not keeping up with technology. allow me to explain.
Chapter 91 of the
Where does most of the oxygen in ocean water (used by fish) come from ? Is it just the surface contact between the atmosphere, and the surface of the water ? (If so how significant are the waves and churning of the water at the surface ?) Is the most important addition to the gases dissolved in the
will a generator run without the capacitor
Hmmmm, I'm not sure what message they're trying to send with the source code of the official webpage of the Democratic People's Republic of Korea. [Daily WTF via The Daily What] More »
Your Help Urgently Needed to Save the Future of Human Spaceflight, SpaceX
"If you care about the future of American space exploration, your urgent help is necessary. The only hope for the average citizen to one day travel to space is in danger due to the actions of certain members of Congress. SpaceX does not have the enormous lobbying power of the big government contractors to stop them, however with your help the day can still be saved.
NASA's Authorization bill (H.R. 5781) will be debated on the floor of the US House of Representatives tomorrow. Despite the imminent retirement of the Space Shuttle, H.R. 5781 authorizes over five times as many taxpayer dollars to fly NASA astronauts on the Russian Soyuz than it invests in developing an American commercial alternative, moreover at a time when jobs are sorely needed in the United States. Quite simply, this bill represents the sort of senseless pork politics that has driven our national debt to the point where our economy can barely service it.
The bill is expected to be brought to the House floor this Friday under a special "suspension of the rules," which is a procedure that limits debate and amendments.
Telephone your Congressional representative right away via the House Switchboard at (202) 225-3121 and ask them to vote NO on H.R. 5781, and instead support the bill unanimously agreed to in the Senate last week.
Your five minutes will make a critical difference, ensuring an exciting and inspiring future in space travel! SpaceX rarely asks you to take action, so you know it really matters when we do.
--Elon--
Look up your representative here."
wat are the mechanical engineering softwares other than the design softwares.
i have area about 500Meters and width 6Meter wide road in that i supposed to used 9Meter lighting pole and i used 250W 220V Metal halide light luminaires & with luminous flux lumen is 19000 how many lighting pole i should be used & how much spacing i should maintain between each pole and my system
whether apple3g is worthfull .wats its interesting features
I understand that gamma ray has higher frequency and energy than x-ray, and could penertrate more depth. But why does x-ray cost more than gamma ray for NDT service?
I love pinhole photography. The fact that people will take a gamble on a piece of film for months—or even years—strikes me as almost romantic, like a time capsule. This longest-ever exposure shows 34months of New York life. More »
They went to investigate solar wind-stirred storms in our planet’s magnetic field, but, after working for three years, two NASA solar-powered probes faced a dark demise, trapped in the Earth’s shadow. NASA researchers now think they can give the twin satellites another shot by altering their courses and sending them instead to study the moon.
NASA launched the probes in 2007 as a set of five identical satellites in the THEMIS Mission (Time History of Events and Macroscale Interactions during Substorms), meant to orbit Earth and send information during brief (2-3 hour) “substorms” when the magnetic field surrounding the Earth releases stored energy from solar winds. To understand the start of these “space tornadoes” responsible for the northern and southern lights, NASA placed the probes in very precise orbits, but for two craft that meant, one day, they would face prolonged battery-draining time in the Earth’s shadow.
“When we realized that the satellites would be going into very deep shadows, we started thinking of different methods for saving them–even before they were launched,” lead scientist Vassilis Angelopoulos, at the University of California, Berkeley, told Discovery News. “We realized that if we had enough fuel to change their orbits, the moon’s gravity would start pulling them up.”[Discovery News]
As Discovery News reports, funding is still pending for the new mission called ARTEMIS (Acceleration Reconnection and Turbulence and Electrodynamics of the Moon’s Interaction with the Sun), but the two satellites are already moonward bound. By firing their thrusters to extend their orbits, scientists started moving them closer to the moon in September of 2009, New Scientist reports. If the mission gets final approval, the recycled probes will move into position 62 miles in front of and behind the moon (relative to the Sun), and will give researchers a look at how the moon’s magnetic fields interact with solar winds.
The gravitational slingshot effect from these lunar encounters, as well as the probes’ close passes near Earth, changed their trajectories drastically – you can see the technical details [and artist renderings] here (pdf). Their own thrusters should be able to do the rest of the job, putting them in orbit around the moon in 2011. . . Not bad for two spacecraft that would have been space junk by now without this creative rescue plan.[New Scientist]
Related content:
80beats: “Space Tornadoes” Power the Northern Lights
80beats: Distant Turbulence in the Magnetic Field Triggers the Northern Lights
DISCOVER: Seeing the Light takes readers to an aurora research station in the Alaskan interior
DISCOVER: Space Weather explains the damage that solar storms can wreak
Image: Artist’s concept of original THEMIS in orbit. / NASA
This morning David and I got up much too early to drive out to hill country in order to collect switchgrass. It was hot, sunny, and muddy, but mission accomplished! On the ride home, we noticed thousands of baby spiders crawling around the back seat, but fortunately, it was his car.
Now to clean up before the afternoon meetings. But first, a question:
During the adventure, our pup got covered in little sticky burrs. I’ve already pulled out several dozen by hand and begun the tedious task of removing the rest with scissors. So I turn to our dog experts out there…
Do you think it’s worth cutting them all out, or will they fall away eventually on their own? Advice welcome and appreciated!
Position of the planets on August 27, 2010. Click for a larger version
The Mars Hoax is beginning to make the rounds again. It just won’t go away. I’m sure you’ve heard it. Mars is going to be the closest it will ever be (or some such claim) and it is going to be as large as the full Moon on August 27th! I’ve even heard all this was going to take place at 12:30 am “so get your cameras ready” and they were going to be close together, oh what an event.
Here’s the real deal. No-No-No-No!! Just go ahead and Google for The Mars Hoax or use any other search engine you please.
Let me take a crack at it too:
Let’s do away with the last bit first. Mars will not be above the horizon at 12:30 am on August 27th. Pretty hard to get that great photo if the planet can’t even be seen eh?
The part about Mars being closest in who knows how long. The image above (click to enlarge) shows the relative positions of the inner planets on August 27, 2010. Note the orbital tracks in the image. The Earth and Mars are a long ways apart on that special day; in fact the next time we will be anywhere close to Mars will be in April of 2014 and we will still be 92,750,760 km or 57,632,650 miles apart!
Let’s compare August 27, 2010 data:
| Moon | Mars | |
| Diameter: | 3,476 km 2,160 miles | 6,792 km 4,220 miles |
| Angular size: | 29′ 15″ | 4.39″ |
| Distance to: (from Earth) | 408,530 km 253,360 miles | 320,000,000 km 198,838,782 miles |
| Magnitude: | 0.00 | 1.52 |
..
Now I know some of you are going “but Tom, your numbers aren’t exact”, yeah I know but they are pretty close.
You can see by not only the image, but looking at that little chart, the angular size (the apparent size of the pair), it’s not even close! The magnitude shows Mars will be dimmer as seen by us – the Moon is going to be 90 odd percent full too. Small and comparatively dim is not large and bright.
Could we on Earth ever see Mars as big as the full Moon? No, but exactly would it take?
We would have to move Mars much closer to us. In order for Mars to appear to be the same size as the Moon we would need to move the orbit in – a lot! From 320,000,000 km to 801,000 km, (that’s from 198,838,782 miles to 497,670 miles for the metrically challenged). Can you imagine what that would do to our tides, to say nothing about other things like rotational and orbital rate?
The other choice would be to move the poor old Moon so its angular size was 4.39″ to match Mars. Moving the Moon from 408,530 km (253,360 miles) to a whooping 163,320,000 km (101,490,000 miles) away would do it. I almost think that would be worse for the Earth than moving Mars closer. I can envision the poor Earth spinning like a raw egg, ahhh, eggs and astronomy, no balancing needed.
So hopefully this will dispel any notion Mars and the Moon will ever appear to be the same size to any person in their right mind as viewed from Earth.
and….I do like Orson Welles 
We are interested in buying all types of sapphire processing equipment. In the first case, automatic diamond section saw, scalping machine, sapphire lapping machine, etc...
I would like to put accent on,that we are a direct buyer, no middleman.
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Those large quantities of nighttime data transfer that appear on your AT&T cellphone bill? It's not new, and it's nothing to worry about—even though somehow it's getting more attention now. It's just routine updates for billing. More »
