Reusable rockets: Up and down and up again

A while back I highlighted SpaceX’s reusable first stage.  Last week, they launched with it with the plan to have it do a controlled descent into the waters off Cape Canaveral.  I haven’t been able to find detailed reports of how well it worked, other than this snippet from their web site.

Data upload from tracking plane shows first stage landing in Atlantic was good! Flight computers continued transmitting for 8 seconds after reaching the water. Stopped when booster went horizontal. Several boats enroute through heavy seas…

While we’re waiting to get more word on this, the Economist has an interesting article on how this might affect the economics of spaceflight.

EVERYTHING about space flight is superlative. Even relatively modest rockets are hundreds of feet high. The biggest (the Saturn V, which launched astronauts to the Moon) remains the most powerful vehicle ever built. But space flight is superlatively expensive, too. One reason is that, for all their technological sophistication, rockets are one-shot wonders. After they have fired their engines for a few minutes they are left to fall back to Earth, usually splashing ignominiously into the ocean.

Rocket scientists have therefore long dreamed of making something able to fly more than once. Such a reusable machine, they hope, would slash the cost of getting into space. The only one built so far, America’s space shuttle, proved a dangerous and costly disappointment, killing two of its crews and never coming close to the cost savings its designers had intended. But hope springs eternal, and several of America’s privately run “New Space” firms are planning to try again.

The furthest advanced is SpaceX, founded by Elon Musk, an internet mogul. On April 18th it is due to launch one of its Falcon 9 rockets on a cargo-carrying trip to the International Space Station (ISS), something it has done twice before. This time, though, the main story is not the ISS mission, but the modifications the firm has made to the rocket itself.

via Reusable rockets: Up and down and up again | The Economist.

As the article discusses, some caution is called for in light of the Shuttle’s history.  Still, if they can make flights cheaper, then many missions that aren’t yet economical might become so.

On the article’s comments about Musk’s Mars ambitions, envisioning one way trips is all the rage these days.  Personally, I continue to think this is a terrible idea.  It’s easy to contemplate something like this with idealized visions of living on Mars.  It’s  quite another to live for months and years in a canned environment, unable to return to Earth until (unless?) you’re able to develop enough industry to build a return launch vehicle.  People who change their mind sometime over those years may come to feel like they’re in the most remote and bleak prison in history.

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The Fusion Game

Originally posted on Ignostic Atheist:

So you’ve always wanted to know how stars work? Fe[26]  lets you fuse your way to stellar oblivion, and it’s free! What more could you want? The goal of the game is to reach a stable isotope of iron, a point at which stellar fusion can no longer progress, short of a supernova. Although the game keeps track of your top score, I personally feel that it should be judged like golf, by how few steps it takes you to reach iron. On the other hand, actually succeeding with a bunch of non reacting magnesiums is an accomplishment.

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SMBC: The evil mathematical universe

A slightly different point of view on the mathematical universe, as only Zach Weiner can deliver.  (Click through to see the full sized version.)

via Saturday Morning Breakfast Cereal.

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Max Tegmark posts his chapter on cosmic inflation online

If you enjoyed my write up on Tegmark’s Level II multiverse, you might enjoy this guest post that he makes on Sean Carroll’s blog, which includes a link to the chapter on inflation from his book, including those visual aids I referenced!

Since the BICEP2 breakthrough is generating such huge interest in inflation, I’ve decided to post my entire book chapter on inflation here so that you can get an up-to-date and self-contained account of what it’s all about. Here are some of the questions answered:

  • What does the theory of inflation really predict?

  • What physics does it assume?

  • Doesn’t creation of the matter around us from almost nothing violate energy conservation?

  • How could an infinite space get created in a finite time?

  • How is this linked to the BICEP2 signal?

  • What remarkable prize did Alan Guth win in 2005?

via Guest Post: Max Tegmark on Cosmic Inflation | Sean Carroll.

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Ugh, really Americans? Poll reveals majority of Americans distrust Big Bang theory

In a new national poll on America’s scientific acumen, more than half of respondents said they were “not too confident” or “not at all confident” that “the universe began 13.8 billion years ago with a big bang.”

via Poll reveals majority of Americans distrust Big Bang theory –

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Tegmark’s Mathematical Universe Hypothesis

Mandelbrot set (Source: Wikipedia)

I recently read Max Tegmark’s latest book, ‘Our Mathematical Universe‘, about his views on multiverses and the ultimate nature of reality.  This is the fourth and final post in a series on the concepts and views he covers in the book.

The previous entries were:
Tegmark’s Level I Multiverse: infinite space
Tegmark’s Level II Multiverse: bubble universes
Tegmark’s Level III Multiverse: The many worlds interpretation of quantum mechanics

This final post in the series is a commentary on the overall book.  Tegmark spends the early parts reviewing the current state of cosmology and physics.  As described in the previous entries, he covers three increasingly diverse and grander definitions of the multiverse.  These are fairly standard multiverse conceptions, and they aren’t all the one in currently circulation, but they are the ones most relevant to his main thesis.

The Mathematical Universe Hypothesis

Philosophy is written in this grand book, the universe … It is written in the language of mathematics, and its characters are triangles, circles, and other geometric figures    –Galileo

Galileo wasn’t the first to say this of course.  The ancient Greeks were also well aware of it.  Mathematics is at the heart of science.  Isaac Newton is credited with explaining the universal role of gravity, not because he was the first to come up with the idea (others had already contemplated it), but because he was the first to demonstrate the mathematics that described its dynamics.

The uncanny usefulness of mathematics in describing the world has often been a source of puzzlement for many philosophers.  Indeed, there is a philosophy of mathematics field where a number of theories about this are discussed and debated, such as empiricism, platonism, nominalism, and many others.

So, the idea that mathematics describes the universe is well accepted.  Tegmark, however, goes further by asserting that the universe is not just described by mathematics, but that it is mathematics, characterizing this as a radical form of platonism.

Now, immediately we have to do an important semantic clarification.  When Tegmark refers to mathematics, he isn’t referring to the notation, the nomenclature, or the techniques that we use to express or explore mathematics.  The ancient Greeks worked in math with a different notation than we use today, and no doubt an alien from Andromeda would have a radically different notation and process than anything humans have conceived of.  But all these notations and processes should refer to the same underlying structures, the same underlying realities.

Tegmark points out that these mathematical structures are often identical to the underlying structures in nature.  We have a tendency to view mathematical structures as abstract and separate from physical reality.  But if those abstract structures match the physical ones, if we have two descriptions that are equivalent, then it makes sense to regard them as describing the same thing.

Many properties in science, such as empty space, the quantum wave function, or the spin property of elementary particles, are really only known only by their numeric properties.  (“Spin” was originally thought to be descriptive of particles rotating in some classical manner.  Subsequent developments showed that to be naive, but the name stuck.)

Most scientific theories are mathematical at their core, but require a qualitative explanation of one or more of the variables.  In physics, this is often referred to as “baggage”.  For example, the equation E=mc2 is fairly meaningless if you don’t know that E is energy, m is mass, and c is the speed of light.

Tegmark speculates that, if the Mathematical Universe Hypothesis is true, then the much sought after Theory of Everything should be a purely mathematical theory.  It shouldn’t need any baggage.  It’s entities should merely serve as points in relationships that should be enough to explain all of reality.

Addressing commons criticisms of the MUH, Tegmark spends a chapter on time.  Mathematical structures are timeless structures, so how does that relate to a universe that evolves with time?  Thinking in terms of spacetime, with time as one of the dimensions, the universe, including all of its history, could be viewed as a static structure.  Tegmark uses the example of a DVD movie that appears to change when watching it, but is actually a static unchanging construct.  He describes this concept in fascinating detail, in a manner that I can’t do justice to here.

Tegmark has an interesting discussion on time, infinity, and strange predictions that may call into question whether infinity is a valid concept.  I found this section interesting because infinity seems to be an important assumption for the Level I and II multiverses.  This discussion also included an excellent description of problems such as Boltzmann brains.

Finally, Tegmark addresses the most glaring criticism, that many mathematical structures do indeed match real world patterns, but not all of them.  Many, such as the Mandelbrot set, exist only abstractly.  Here is where all the earlier discussion of multiverses come to fruition.  Tegmark’s answer is that all mathematical structures correspond with actual physical patterns, just not all in this universe.

The Level IV multiverse is one of mathematical structures.  If our universe is a mathematical structure, then it is only one of an infinite variety of structures.  All mathematical structures have physical reality in this multiverse.  Exploring this multiverse is a matter of computation and ideas.

My take

Before reading this book, I was agnostic about the MUH, and I’m forced to say that I remain largely agnostic, albeit now in a much more informed fashion.  Tegmark does an excellent job of describing the concept, along with the many required supporting ideas.  But I often found him to exude a level of certainty that felt unwarranted.

His certitude is often related to what he sees as the inevitable mathematical consequences of well accepted theories.  I don’t understand the mathematics of most of those theories well enough to judge first hand whether or not that certitude is warranted.  But I’m aware that many physicists, who do understand those theories at the mathematical level, don’t necessarily concur.

I’m also aware that just because the mathematics lead to a certain conclusion doesn’t make that conclusion inevitable.  The mathematical consequences of Newtonian mechanics allowed astronomers to predict the existence of Neptune because of Uranus’s orbit, but it also led them to predict the existence of Vulcan because of Mercury’s orbit.  One was right, but the other was wrong, and a new theory (general relativity) was necessary to understand why.

I do strongly believe that mathematics rest on empirical foundations, foundations found in the patterns of nature.  As a result, many mathematical constructs have real world correlates, and many others approximate real world patterns.  This, to me, is sufficient to explain the powerful utility of mathematics in science, without necessarily having to  adopt an absolutist position about all mathematical structures having physical existence.

Of course, many abstract mathematical structures have no known physical correlates.  Here Tegmark’s extensive descriptions of multiverses serve an important purpose, since multiverses are necessary to explain how these abstract structures could exist physically.  Interestingly, Tegmark himself does speculate that some mathematical structures might actually not exist.  His focus is on infinite ones, but it doesn’t seem like much of a cognitive leap to conclude that many other types might not as well.

But if those abstract structures don’t have a physical existence, then where do they come from?  I’m tempted to say that they come from the same place as Vulcan, that is a tautological conclusion with no real world correlate.  But this implies that they’re not valid, and I don’t think that, particularly since abstract structures sometimes turn out to correspond to something physical that we just weren’t aware of when they were formulated.

To be clear, I do think the MUH is a valid candidate for reality.  It might be true.  In the first post on this blog, I discussed the possibility that reality might be structure all the way down, and the MUH is definitely compatible with that.  Even if reality does have a brute physical layer, everything above it are patterns, most of which, if not all, are describable in mathematical terms.

I tend to think that whether or not the MUH is true is a philosophical matter.  Tegmark asserts that the idea is falsifiable since if it isn’t true, physics will eventually hit a brick wall where mathematics is no longer useful.  The problem is that if we hit such a wall, MUH proponents can always claim that we simply don’t know enough yet to apply mathematics to that wall.

Indeed, a case could be made that this is exactly what the indeterminancy of a single quantum particle is, and that quantum interpretations that rescue determinism are just saving appearances.  Now, I’m agnostic on the major quantum interpretations, and I certainly don’t think it’s productive to assume we’ll never know more than we do about it, but it does seem that the MUH needs one of the deterministic interpretations of quantum mechanics to be true.

All that said, Tegmark is an excellent writer, and if you’ve found the ideas in this series interesting, then I highly recommend his book.  It’s an excellent introduction to many ideas and I’ve only lightly scratched the surface in this and the previous posts.

Additional reading

Fellow blogger, Disagreeable Me, a advocate of the MUH, has written an excellent blog post on it, which I know some of you have already read.  DM approaches the issue from a philosophical angle, and I found myself returning to his post after I had completed the book.  A highly recommended read.

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Is Philosophy Obsolete? – The Chronicle Review

Rebecca Goldstein appears to be on a campaign to defend philosophy.  In this essay, she defends its ability to make progress, and questions whether it should be lumped in with the humanities.  (I wonder what the humanities folks will think of that.)

Philosophy was the first academic field; the founder of the Academy was Plato. Nevertheless, philosophy’s place in academe can stir up controversy. The ancient lineage itself provokes dissension. Philosophy’s lack of progress over the past 2,500 years is accepted as a truism, trumpeted not only by naysayers but even by some of its most enthusiastic yea-sayers. But the truism isn’t true. Both camps mistake the nature of philosophy and so are blind to its progress.

via Is Philosophy Obsolete? – The Chronicle Review – The Chronicle of Higher Education.

I do think philosophy has enormous value.  Much of what I discuss on this blog is philosophy.  And it does make progress.  Unfortunately for philosophers, that progress is typically measured across centuries, and it appears that ground breaking philosophers are rarely celebrated in their own time.

I do think the field suffers from tolerating too many kooks in its ranks.   It seems to share this problem with economics, although they arise for different reasons in each field.  In the case of economics, it comes from politics.  In philosophy, it may be an unavoidable consequence of being open to new modes of thought.  But in both cases, it gives critics ammunition to question the entire field.  If philosophy is really about making things more coherent, then the incoherent should be excluded.

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