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Contents of the Universe: Dark Matter and Dark Energy

Amazingly, 95% of the make-up of the universe is stuff we can't see, according to cosmologists. Find out more about dark energy and dark matter, which far surpasses the amount of visible mass in the universe.

Physics Spotlight10

Susskind's Theoretical Minimum Coming Out in Paperback

Sunday April 13, 2014

Book Cover of The Theoretical Minimum by Leonard SusskindLeonard Susskind's phenomenal book The Theoretical Minimum: What You Need to Know to Start Doing Physics is slated for a paperback release on April 22, 2014. For anyone who seriously wants to confront the challenge of actually doing physics - instead of just learning about all the cool stuff that physics talks about - this is really an essential book. Every student who has any hope of moving forward into the study of physics or engineering would do well to have this book on their "to read" list. The strong presence of mathematics isn't for the faint of heart, but it's a level of mathematics that anyone with an interest in physics or engineering will need to become familiar with. (See "What Skills Do I Need to Study Physics?")

The sequel, Quantum Mechanics: The Theoretical Minimum, came out at the end of February. A review on it is coming soon ... but if you haven't read the first book yet, then your chance to get it in paperback is coming up.

The Physics of Captain America

Friday April 4, 2014

The Physics of Superheroes coverEver since reading Jim Kakalios' The Physics of Superheroes, I've been intrigued with the science of how superheroes do the things they do. While this usually manifests in the more grandiose elements of the superhero world, with questions like "How can Iron Man fly?" or "What all can Magneto manipulate with his magnetic powers?" it can show up in much more mundane places as well.

Toward that end, the fine folks over at Wired magazine's Dot Physics blog have taken a commercial segment where Captain America catches his thrown shield and turned it into a problem that incorporates friction, Newton's third law of motion, and the principle of conservation of momentum toward an entirely worthy goal: determining the mass of Cap's shield.

The process is available on their blog, along with some nice little free-body diagrams. For those who don't want to work through the calculations, though, the results come out to the shield having a mass of about 19.9 kg. This means a weight of about 43.9 pounds, which is a pretty heavy shield and certainly hefty to throw, though probably not for someone enhanced with super-soldier serum.

The author then goes a step forward to consider the density of the shield, and here I think we run into some problems. Using some additional estimates, he arrives at  a pretty broad range: 87 8767 - 4383 kg/m3. This range extends from a bit more dense than iron to less dense than titanium, so it is a reasonable range, in principle, but the Vibranium alloy that composes Cap's shield may give some additional clues. Here is from The Physics of Superheroes on the subject:

Wolverine's claws are composed of pure Adamantium, but Captain America's shield is a one-of-a-kind alloy of steel and Vibranium. The steel is needed to provide rigidity, so that the shield can ricochet off walls and supervillain minions. Vibranium is an extraterrestrial material brought to Earth when a meteorite crashed in the African nation of Wakanda, which is ruled by the superhero the Black Panther. Vibranium has the ability to absorb any and all sound and convert the energy in the sound wave into some other, not-well-specified form, making it the perfect shock absorber, a quality strongly desired in a shield.

Kakalios doesn't specifically address the density of Vibranium, but I find it unlikely that something with the ability to absorb sound waves would be more dense than iron, so my guess is that this would at the very least be at the lower end of this spectrum. In part this seems justified because the special properties of the Vibranium alloy would indicate that we can stick with the thinner shield estimate and still have an effective shield.

What do you think? Does that shield look like it weighs over 40 pounds?

3 Weeks In, Cosmos is Shining Brightly

Tuesday March 25, 2014

Cosmos-A-SpaceTime-Odyssey-Official-Facebook-Page.jpgThe scientific television event Cosmos: A Spacetime Odyssey has aired three of its thirteen episodes so far, and I, for one, am extremely impressed with what I've seen. When the series began, I asked if it could really live up to the hype and I'm fairly sure that it's at least coming close. Though the core science in each episode is well established and won't be new to anyone who has studied science to any depth, it is presented in an engaging and entertaining manner that makes it accessible even to viewers who may never have been exposed to the concepts before. For those of us who know the basic facts, it's still good television. The historical treatments and little details sprinkled throughout offer enough insights that I've discovered a couple of new things in each episode. Again, I cannot commend FOX enough for the risk they took in embracing this project, and I truly hope it is successful and shows television executives that thoughtful television does have an audience in America.

If you haven't yet seen the series, then I do recommend that you check it out. If nothing else, this will at least help offer solidarity in support of intellectually-stimulating television programming!

The series is available for streaming free on their official website and also through Hulu. Busy and don't have time to watch the full episodes? Well, check out our recap of the episode highlights:

Let us know what you think of Cosmos: A Spacetime Odyssey in the comments below!

Gravity Waves Seen From Post-Big Bang Inflation

Sunday March 23, 2014

A timeline of the history of the universe. (June 2009) - NASA / WMAP Science TeamPhysicists have detected gravity waves in the light left over from the Big Bang, which hints that a 30-year-old cosmological theory that potentially bridges the divide between the largest and smallest scales in our universe might be on the right track.

For decades, scientists have widely accepted the Big Bang theory as the leading cosmological description of the universe's earliest moments. The real nail in the coffin of alternative theories was the discovery of the cosmic microwave background (CMB) radiation in 1964, which matched closely with the theoretical predictions about the existence and value of this remnant energy left over from the earliest universe.

But this most certainly did not mean that all questions about the early universe had been answered. As more data came in from astronomers, it became clear that the universe had properties which cosmologists would like to explain, but which were not specifically determined by the Big Bang theory itself. How to explain, for example, the fact that the universe looks roughly the same in all directions (called the homogeneity problem). Or how could they explain the fact that the spacetime geometry appeared to be so flat (called the flatness problem)?

In 1980, the particle physicist Alan Guth took a stab at this problem. Together with colleagues, he worked to apply cutting edge understanding of the quantum physics at work at the smallest scales of reality to figure out what might have been going on in the early universe. The result was a prediction that the early universe would have been incredibly unstable and, within the first second of the big bang, would have undergone an immense expansion. The resulting theory became known as inflation theory and in the three decades since, it has become widely accepted among physicists of all stripes.

Part of the reason for this is that all evidence we've gathered from observational projects such as WMAP and others have supported the predictions of inflation. But there were, in fact, some other suggestions that might have explained these different phenomena as well. So while physicists broadly believed that inflation was probably true, they didn't yet have a key piece of direct evidence to confirm it over and above the rival theories.

Fortunately, inflation theory did offer a very precise prediction that was offered by no other competing theory. During the rapid expansion in the earliest instance of the universe, the very fabric of spacetime itself would have been distrubed, sending undulating ripples throughout the universe itself. These gravity waves (called the Cosmic Gravitational-Wave Background or CGB) would be incredibly difficult to detect, but the theory predicted that they would result in a polarization of the cosmic microwave background itself ... and inflation theory also predicted precisely the level of polarization that was expected!

All that was required was for technology to catch up with theory and become refined enough to detect whether or not this polarization existed. On Monday, March 17, 2014, the BICEP2 collaboration group announced results that confirmed the first direct evidence of inflation theory. Using advanced telescopes mounted at the South Pole, they detected precisely the polarization predicted by the inflation theory. Specifically, they detected that the CGB had a B-mode polarization with a value of r = 0.2.

This is being broadly heralded as confirmation of the inflation theory, although I should be quick to point out that it would need to be confirmed by other experiments. Fortunately, there are several in place to do just that. If confirmed, however, it would seem to be about as solid confirmation as a theory could have, so inflation theory will become even more widely accepted within the physics community. This evidence represents the earliest evidence we've found about anything that happened in our universe and, in the words of physicist Clifford Johnson's Asymptotia blog:

Those tiny scales are knocking on the door of the kinds of things I work on - quantum gravity. The very young universe had both quantum physics and spacetime physics (gravity) doing important things together and the combination of the two "quantum gravity" is what we hope to understand and put to the test one day, whether it be string theory or some other approach we may or may not have thought of.

Though there's likely not going to be any practical application to this discovery, this sort of confirmation is definitely the sort of thing that could set Alan Guth and the other creators of inflation theory on the track for a Nobel Prize. Amazingly, we have possibly one of the most fascinating historical records if that is the case. One of the physicists working on the experiment notified Andrei Linde (one of the co-creators) of the discovery ... and recorded it. If confirmed in the next couple of years, we therefore have the possibility of the first Nobel Prize in Physics that was heralded in with a viral YouTube video!

Image: A timeline of the history of the universe. (June 2009), Source: NASA / WMAP Science Team

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