Category Archives: astrophysics

Books about space and how it works.

Review 218: Why does E=MC2?

LL 218 - Why Does EMC2Why Does E=mc2? by Brian Cox and Jeff Forshaw

Way back in the mists of ancient time, when I was a college drama student, we all went down to New York City to see Tom Stoppard’s Arcadia. I don’t remember much of it now, but I remember it had to do with math and fractals, time and space, and that when the play was over and we all went outside for a smoke, I had a moment of what could only be called sublime clarity. I stood out there with my cigarette, staring off into the middle distance, and – for just an ever-so-brief time – I understood everything.

Not the play, mind you. Everything. It all made sense. It was nothing I could have put into words or explained in any period of time shorter than a lifetime, but it all worked. It all fit together, and I knew what the universe was and what my place in it was. It’s probably how Fenchurch felt in The Hitchhiker’s Guide right before the Earth was demolished.

It... it all makes sense now.

It… it all makes sense now.

And that feeling was wonderful.

It passed, though, because no one can be allowed to hold on to that kind of clarity of understanding. We’d never get anything done. By the time I got on the bus, I was trying to claw my way back to it, understanding but not caring that this was a place you couldn’t find the same way twice. The fine, crystalline perfection of the universe had once again been hidden from my mind, and all that was left was the memory of what it had felt like to know that everything was as it should be.

Reading this book was kind of the opposite of that experience. On every page, I knew that if I would be able to hold on to these ideas just a moment longer, if I could just put the pieces together a little faster, then I would have true understanding of the elegant beauty of creation. But I couldn’t, and I was left with the feeling that it was my own shortcomings that were at fault, rather than those of the authors.

Cox and Forshaw have set a very interesting challenge for themselves in this book. They want to explain one of the most famous equations in human history, and to do it in such a way that the non-scientist reader can understand not only what it means, but where it came from and what its implications are. This is no mean feat, of course, on any front. For all its simplicity, E=mc2 contains within it some of the most important and fundamental understandings about how the universe works. To truly understand this equation is to understand time and space, matter and energy, existence in four dimensions and at scales both vast and tiny.

They begin with what looks like a very simple question: where are we? Galileo pondered this question for a while, and came up with an answer that was probably both enlightening and horrifying for his time.

We don’t know.

Very helpful, thank you.

Very helpful, thank you.

Oh sure, we can know where we are in relation to something else – between a pair of arbitrarily numbered latitude and longitude lines, for example, or at a position around the star that we orbit. But a moment’s thought reveals that we still need to explain where the reference point is, and that we can only explain that in relation to something else, which can only be positioned by yet another relative measurement. In other words, there is no such things as an absolute location in space. There is no universal “there” there by which we can understand the position of anything.

Man, that must’ve freaked him out.

The next insight is that if there is no absolute place, then there also cannot be any absolute motion. As I type this, I am sitting in my comfy chair. As far as I’m concerned, I’m motionless. But I’m not. To an alien on the moon, I’m moving with the Earth’s rotation, whipping past at a breakneck pace of about 1,600 kilometers per hour. On top of that, the Earth is moving around the sun at over 100,000 km/h. which is in turn dragging the whole solar system around the center of the galaxy at roughly 220 kilometers per second, and the galaxy itself is moving through intergalactic space at over 600 km/s, and space itself is expanding at what can only be Ludicrous Speed.

So questions that seem like they should be simple turn out to be really hard to answer. But what comes next is even worse: if there is no absolute place or motion, then what about time? How can we have an immutable, fixed time if there is no such thing as an immutable, fixed place?

Look, I don't know how to make it any simpler than this.

Look, I don’t know how to make it any simpler than this.

Cox and Forshaw proceed to lead us by the hand through the discoveries and realizations of scientists such as Faraday and Maxwell, with a little bit of Pythagoras and Galileo, before bringing us to Einstein and beyond. Through the use of lightspeed trains, mirror-clocks, and a whole variety of illustrative analogies, they take us step-by-step through the process of moving from our understanding of three-dimensional semi-Euclidean space to a four-dimensional spacetime. They guide us through physics and geometry, on scales both large and small, and show not just what E=mc2 means, but how Einstein got to it, and how we’ve proven it so far.

In that sense, this book is a great success. The popular vision of Einstein is that he came up with Relativity because he was bored at work, and that it popped into his head fully formed. But without the work of countless scientists before him, Einstein wouldn’t have had a place to start. E=mc2 is built on the foundations of meticulous science, and is supported by a logical structure that is both elegant and simple. What’s more, his theories of relativity have been tested again and again in all kinds of ways, and they have stood up to those tests. And not for lack of trying, mind you – there isn’t a physicist alive who wouldn’t be thrilled to prove Einstein wrong and propose a more accurate version of reality. But so far, it seems to be the best explanation there is.

For all their care and meticulousness, however, the book is still a bit tough to get through. One of the things that got in my way was how they constantly apologized for using math. I understand why they did it – a lot of adults have a hate-fear relationship with math, and especially equations that start using letters. Math still has an element of mystery and wizardry about it, at least if you’re not very proficient in it, and I get that they didn’t want to scare off any math-phobics from their book.

Wau!

Wau!

But at the same time, I think I would rather they had said, “Okay, follow along with us – it’s about to get MATHTASTIC!” Well, maybe not those words, but I started to get a little tired of being talked to like a timid child as the book went on. They said over and over that I could skip the math parts if I wanted to, and sure enough that’s what I ended up doing. But I think I would have come out of this book with a much better sense of understanding and accomplishment if Cox and Forshaw had said, “We’re going to do math and you’re going to understand it.” As it is, they talked to me like I was a slightly dim child, and I still didn’t fully understand. So what, then, does that say about me?

That I seriously overthink things, for a start.

In any case, even if I didn’t get the math, and didn’t see where all their conclusions came from – especially when they started going over the Master Equation of particle physics near the end – I at least came away with a better understanding of both the chain of reasoning that led to E=mc2 and the ramifications it has on our understanding of the universe. I don’t understand everything this time, at least not yet, but I know more. And that will have to do.

—————————–
“Science at its best is driven by inquiring minds afforded the freedom to dream, coupled with the technical ability and discipline to think.”
– Brian Cox & Jeff Forshaw, Why Does E=mc2?

Advertisements

Leave a comment

Filed under astronomy, astrophysics, Brian Cox, Jeff Forshaw, mathematics, physics, science

Review 132: Cosmos

Cosmos by Carl Sagan

If you’ve known me for more than a little while, you know that one of my great loves in this world is science. Even though I tend to get stymied by the math, and I probably couldn’t call up all the right data from my head at the right time, it is the idea of science and the stories of science that truly interest me. Just the fact that we live in a universe where it is possible to know how things work, where we can devise a way to look at the whole of creation, from things so large that they defy imagination to things so small that they can barely be said to exist at all. Science is imagination put into practice against the universe, and as much fun as stories and myths are, as hope and prayers may be, science is the best, most reliable way for us to come to grips with the Cosmos.

It is to Carl Sagan that I owe this love of what humans have done with ourselves.

Go ahead. Stare at this for a while.

When I was a kid, my father had a copy of Cosmos, and, since I was but a child, I never really read it. I tended more to flip through it for the interesting pictures – the speculative Jovian life forms on pages 42 and 43, the Viking photos of Mars in chapter 5, the gorgeous paintings of the views from other worlds around other stars, the photos of nebulae and galaxies, all of these things fascinated me, and if I had been a bit more patient I would have found out about them. But I was a kid, so that can be excused. What the book did for me was to open my mind to a universe of possibilities that were all within our reach, or at least would be someday.

As I got older, I saw the TV miniseries of the same name on PBS. Now the pictures that I had lingered over in the book were right before me, accompanied by Sagan’s soothing baritone. His ship of the imagination somehow managed to take us unfathomable distances from our home and bring us back again. He talked to his viewers like we were intelligent adults, fully capable of understanding and appreciating the vast scope of scientific discovery rather than a bunch of attention-deficit teenagers who couldn’t be trusted to keep watching without a jump-cut every ten seconds. Carl Sagan believed, despite the occasional evidence to the contrary, that human beings were capable of overcoming our barbaric pasts and forging a bright new future together in the stars.

The purpose of Cosmos, both the book and the TV show, was to educate. It was, as Sagan put it, “to engage the heart as well as the mind,” perhaps to help shed the image of science as a cold and passionless pursuit. He wanted to show how science became what is is, from the ancient scientist/philosophers in Ionia and Alexandria all the way up to the engineers and astronauts working at NASA. It’s all part of a long chain of knowledge that ties human history together and which engages one of our deepest desires: to know how the universe works.

Go ahead, do this one yourself. We'll wait.

Each chapter focuses on a different theme of knowledge – from the way the planets form and what they’re like to the nature of the furthest reaches of space. He starts with how Eratosthenes measured the world with just a shadow and some math, and how the ancient thinkers of Alexandria were asking the same questions about the nature of the Earth that we ask today. He follows the tortured path of Johannes Kepler in his quest to understand how the planets move, the arrogant brilliance of Newton as he completely redefined the clockwork of the cosmos, and the casual miracle that Einstein pulled off when he told us that not only are we not the center of the universe but that there is no center. Each great mind led to another.

Unfortunately, each setback cost us what may be valuable time. For all his wonderment, Sagan understood how petty and ignorant human beings could be. From the beginning, and at various points in the book, he reminds us of the millennium we lost with the destruction and corruption of the ancient thinkers of the Mediterranean. As far as we can tell, the men and women who made their home in Alexandria were investigating questions and scientific problems that would have changed the way we understand the world. If the library hadn’t been burned down, if religious terror hadn’t murdered scientific insight, who knows where we would be today? It’s impossible to know, but it’s tempting to think that we might have been well on our way to the stars by now.

My brother gave me this poster. He knows me so well...

The latter chapters underscore that theme pretty heavily, reminding us over and over again that we have one world, and only one world. Not only does Sagan fear that we could obliterate ourselves with the nuclear weapons we love and fear so much, but he also fears that self-annihilation may be a natural outcome to any intelligent civilization. Our search for intelligent life on other worlds may be fruitless, because they might be just as self-destructive as we are.

But we don’t know. We can’t know, at least not yet. Our understanding of the universe is still not clear enough, our technology is still not good enough, and perhaps it never will be. But for all our stumbles and failures, Sagan wants us to remember and understand just how much humanity is capable of, and how good we could be if we really put our minds to it. And in that sense, there is a lot of value to reading it now, thirty years after it was published.

A glorious dawn indeed....

While we have not eliminated nuclear weapons, we have made great strides towards controlling them and reducing their numbers. The hopes that Sagan had for future space exploration – Mars rovers, a probe to Titan, contact with comets – have all been made real, and with outstanding results. We know that the dinosaurs were wiped out by a meteor impact – something that Sagan is clearly unsure of at the time of writing. We have mapped the human genome and developed personal computers that have revolutionized the way we explore space. With the internet, any person on earth can catalog galaxies or explore the moon, there have been advances in nanotechnology and materials and bioengineering and evolution that would have made even Sagan’s eyes pop.

Despite all our flaws, we continue to advance. We continue to build knowledge upon knowledge and to further our understanding of how the universe works. Maybe we will one day leave this planet ourselves, perhaps just for a visit or perhaps to start a new world. Maybe if we persist in our quest to comprehend the world we live in, to shut out the howling and screaming of the voices of unreason, we can make the world a better place for generations to come.

Maybe we should all just have some pie. How much time do you have? (photo by Nicole)

In the great argument that is raging these days between the rationalists and the believers, the faithful and the atheists, it has become fashionable to try and shout the other side down. To adopt a position that excludes compromise and promises only defeat for one side or another. Sagan never would have wanted that, and I think he hit upon a solution that needs to be revisited.

Rather than try to turn people to science through cold logic or heated words, through derision and coercion and fear, do as Sagan did: win them over with wonder. The cosmos is too big, and there is too much to know to waste our time with petty arguments and pointless feuds. If you want people to appreciate science, turn to people like Sagan, or Neil deGrasse Tyson, Phil Plait, Mary Roach, Michio Kaku, Ann Druyan, Bill Nye, Adam Savage, or Dava Sobel – people whose enthusiasm and love of science will instill people with wonder, one person at a time. And it is in that way that we will go furthest towards ensuring humanity’s place among the stars.

—————————————————-
“Every one of us is precious in the cosmic perspective. If a human disagrees with you, let him live. In a hundred billion galaxies, you will not find another.”
– Carl Sagan, Cosmos

Carl Sagan on Wikipedia
Cosmos on Wikipedia
The Carl Sagan Portal (music plays when you open it, just FYI….)
Cosmos on Amazon.com

Leave a comment

Filed under astronomy, astrophysics, Carl Sagan, evolution, made into movies, nonfiction, science

Review 34: Death by Black Hole


Death by Black Hole by Neil deGrasse Tyson

I have often lamented the passing of my favorite popular scientist, Carl Sagan, by talking about how necessary he is right now. We are at a point in our history where scientific illiteracy is growing, where people are not only ignorant of how science works, but are proud of their ignorance. What we need is someone who can reach the majority of Americans who are not especially scientifically literate – the people whose automatic reaction to science is to think, “That’s just too hard for me to deal with.”

Enter Neil deGrasse Tyson, an astrophysicist and the director of the Hayden Planetarium at the American Museum of Natural History in New York City. He’s appeared on countless television programs, including The Daily Show and The Colbert Report, to talk about the current state of astronomy and astrophysics. He’s an engaging and entertaining man, who claims that Pluto was “asking for” its demotion, who seems to take perverse pleasure in describing all the terrible ways the universe could take us out. He knows that we’re in a precarious position, here on Earth, and he revels in it rather than worrying about it.

Whereas Sagan seemed to come from the point of view that the universe was a place of infinite wonder, where one could look anywhere and be awed and humbled, Tyson’s attitude is more of the universe as an infinite theme park – a place where you could see your electrons stripped from your body, watch gas clouds larger than our own solar system collide and ignite, or see planets crumple under cosmic bombardment. Tyson’s universe is an adventure, as big as it gets.

This book is a collection of essays that Tyson wrote for Natural History magazine over a ten year period, on a variety of subjects related to science and scientific inquiry. In many ways, it’s similar to every other pop science book out there – and there are so very many of them – but it is his perspective and his voice that makes this one stand out from the crowd.

He’s grouped his essays into seven sections, on topics ranging from the difficulties inherent in actually knowing anything about the universe to the understanding of how life went from little mindless bacteria to we clever Homo sapiens to the intersection of science and religion. Most of it is accessible to the average non-scientist, though he does get a little technical at points. But he understands that, and he tries to compensate for for the fact that, by and large, the public is intimidated by “real science.” In the essay entitled, “Over the Rainbow,” he discusses this particular challenge by using spectroscopy as an example.

In spectroscopy, astrophysicists look at the spectrum of a star, hunting for telltale dark lines that indicate the physical properties of stars. It’s like looking at a rainbow with bits blackened out of it, as though the CIA had somehow gotten to it first. Those black lines contain all the vital information about the star’s composition and, more importantly, speed. Very little can be gleaned by just looking at the star, as it turns out. He notes five levels of abstraction, starting from the star itself:

Level 0: A star
Level 1: Picture of a star
Level 2: Light from the picture of a star
Level 3: Spectrum from the light from the picture of a star.
Level 4: Patterns of lines lacing the spectrum from the light from the picture of a star.
Level 5: Shifts in the patterns of lines in the spectrum from the light from the picture of a star.

These descending levels of abstraction can apply to any branch of science, not just astrophysics. The challenge, as he notes, is getting people past level 1, which is easy to understand but is not the level at which true science is done. It is up to educators, he says, to help make people comfortable with looking at real science, and not just pretty pictures.

Indeed, there are several sections of the book dedicated to the intersection between science and the public. He talks about how easily we are baffled by numbers (why are below-ground floors not labeled -1, -2, -3 etc?) and how casually we disregard actual scientific facts. He brings up some of his favorite moments in bad movie science, and how he single-handedly saved Titanic from ignominious astronomical shame. At least, on its DVD re-release. He addresses the historically shifting centers of science in human history, how things like NASA are truly a global endeavor. Without the discoveries made through history by people all over the planet – from England to Greece to Baghdad – there would be no NASA, nor any science that we recognize. And to assume that the United States will always be the center of scientific discovery is to willfully ignore history.

And, of course, there’s a section dedicated to the conflict between religion and science, a never-ending battle that has existed since science began. Tyson believes that there can be no common ground between the two – science relies on facts, religion relies on faith. This is not to say that one is better than the other, any more than, say, a hammer is better than a screwdriver. It’s just that you can’t use them interchangeably. And he points out that becoming a scientist doesn’t require you to give up your faith. There have been, and still are, countless scientists who are believers in the Divine. It’s just that most of them know enough not to confuse science and spirituality.

The place where they meet, historically, is on the boundary of ignorance. Isaac Newton, having figured out gravity, couldn’t quite work out how you could have a multiple-body system like our solar system without the whole thing falling into chaos. His conclusion – God must, from time to time, step in to keep things on the right path. Having done that, Newton went on to do other things, and it wasn’t until the next century that Pierre-Simon laPlace decided that he wasn’t satisfied with Newton’s “Insert God Here” argument, and did the math for himself.

In other words, God is a marker on the boundaries of ignorance, and the best of us are tempted to let Him answer the questions that we can’t. To do so, however, impedes the path of science and stops progress in its tracks. What if Newton had said, “No, I’m going to figure this damn thing out.” Would we be a century ahead in our technology by now? Maybe, maybe not. What if the Catholic Church had listened when Galileo said, “The Bible tells you how to go to heaven, not how the heavens go.” Might more progress have been made? So many great thinkers have come up to the boundaries of their knowledge and, humbled by what they do not know, chose to allow The God of the Gaps reassure them.

But that’s the whole point of science, and it’s what this book, and others like it, are trying to instill in people. The unknown is not horrible, it is not terrifying, and it’s not a place to just stop. It’s a place of awe and wonder and bafflement and opportunity. To say, “I don’t understand it – it must be God” is short-changing ourselves and our heirs out of even greater knowledge of the universe.

—————————————————-
“Scientists cannot claim to be on the research frontier unless something baffles them. Bafflement drives discovery.”
– Neil deGrasse Tyson, Death by Black Hole
—————————————————-

Neil deGrasse Tyson on Wikipedia
Death by Black Hole on Wikipedia
Death by Black Hole on Amazon.com
The Hayden Planetarium

Leave a comment

Filed under astronomy, astrophysics, Neil deGrasse Tyson, nonfiction, science

Review 24: Death from the Skies!


Death From The Skies! by Phil Plait

I’ve always found the end of the world fascinating. So many cultures have put together their own ideas of how the world will end, from the Norse Ragnarök to the Christian apocalypse to the Hindu cycle of creation and destruction. We live in a world that was, for a long time, unpredictable to us and on many occasions seemed to be outwardly hostile. Our ancestors faced floods and earthquakes and disease, with no idea of where these things came from, why they happened or how to stop them. And so they made myths and stories to explain the dangerous world in which they lived. From that, they extrapolated – if the world is this dangerous now, how dangerous could it be if it really tried? And so came our myths of a world that not only succeeds in hurting us, but in wiping us out altogether.

Even in the modern age we have our myths. Books, television, and movies all use the end of the world (or end of a world) to tell stories – usually about the resilience of mankind and our ability to pick ourselves up, dust ourselves off, and rebuild human society, hopefully for the better. As good as this is for fiction, there are two problems when we try to apply these myths and stories to the real world: the world will end, one way or another, and no amount of heroics, cleverness or pluck will save us. Not in the long term, anyway.

Science has accomplished what religion and fiction could not – it has seen the future and can make fairly accurate prophecies about how this world, and our civilization upon it, will die. Renowned astronomer Phil Plait is your prophet for this trip into all the ways the world will end….

In this book, Plait looks at nine possibilities for the end of the world as we know it. In order, they are:

Death by Impact
Death from the Sun
Death by Supernova
Death by Gamma Ray Burst
Death by Black Hole
Death by Aliens
Death of the Sun
Death by Galactic Collision
Death of the Universe

In each chapter, Plait outlines the ways in which that specific event could injure or kill us, with as much science as he can comfortably put in. He explains, for example, why we can’t just send Bruce Willis up to hit an incoming meteor with a nuke (it probably won’t work) and why any black holes produced by the LHC won’t do us any harm. He looks at how a supernova happens, what it is about a black hole that turns it into one of the deadliest weapons in the universe, and tries – very, very hard – to make the reader understand exactly how long “forever” is. (Hint: it’s a lot longer than you think. Longer than that, even. Nope, keep going….)

Each chapter outlines the processes by which we could experience the destruction of our civilization or, in a few cases, the planet itself. He looks at the scientific foundations of these events, explaining in detail what it is about the sun, for example, that makes it a cauldron of chaos and torment, or why we really, really don’t want to get even a smallish black hole anywhere near the planet. And I have to say, of all the unlikely ways we could be toasted, gamma ray bursts are my favorite – a deadly beam of energy from thousands of light-years away, cooking the planet all the way down through the crust and utterly devastating the planet’s ecosystem so as to kill off anyone who was lucky enough to be on the other side of the world. I mean, wow. And there’d be no warning, either. By the time we knew what was happening, it’d be too late. So that chapter (with a line paying homage to Douglas Adams, even) is just mind-boggling.

Probably my favorite chapter, though, is the one about supernovas, mainly because his careful, step-by-step description of exactly how a supernova occurs made me think, “What I wouldn’t give to see that in person,” disregarding the fact that a) the best parts would happen way too fast for me to observe and b) it would vaporize me. Still, it’s a beautiful and terrifying chain reaction, which Plait describes in fantastic detail. The other chapter that evoked the same reaction was the one on the end of the universe. Despite timelines for which the word “vast” is terribly inadequate, Plait tells us what science knows about how the universe will end – the ever-increasing expansion of spacetime, the eventual death of the stars, evaporation of galaxies, the reign of the black holes and the slow, careful deaths which even they face. It all ends in darkness, all matter gone into a few stubborn subatomic particles and the eventual collapse of the very fabric of space and time.

And as bleak and miserable is the future looks, I still thought, “I really want to see that.” So if I can figure out how to live one googol years (that’d be a one with one hundred zeros after it [1]) and not have my very atoms decay into nothingness, then I’ll be able to… um… be really, really bored, probably. Since after that, there’s absolutely – literally – nothing to do. Until the universe experiences vacuum collapse, or a brane collision, possibly hitting the reset button on the cosmos and we get to do it all over again….

Most of what’s in the book isn’t new to me, but that’s probably because I grew up reading Cosmos, and I follow countless science TV shows, podcasts and blogs (including Plait’s own Bad Astronomy blog, which is well worth keeping up with, as well as his regular appearances on SETI’s podcast, Are We Alone? and occasional guest appearances on The Skeptics’ Guide to the Universe – both of which make for excellent listening). For people new to astronomy, though, this will be a rather dense learning experience – and reading it will be time well spent.

In addition to its user-friendly style, I really like the way it’s arranged – from small-scale (relatively) to large, with “Things that are absolutely certain to happen” at the beginning and end, and with “things that probably won’t happen” in the middle. And my favorite aspect of this book is that each chapter begins with a short vignette describing that particular end of the world, from the perspective of someone watching it happen. It’s not something you often see in books of this nature, and I’m really glad that Plait decided to put it in there. It makes it a little less academic and abstract and more real.

For all its death and destruction, the book isn’t really a downer. For one thing, while things like asteroid impacts and the death of the sun are inevitable, they don’t have to be fatal, and Plait describes a few ways in which – in theory – we (or our distant, distant descendants) might be able to avert or at least mitigate these catastrophes. It’s not easy, of course, but saving the world never is.

It’s mainly a marvel at the forces that surround us in the universe. It’s easy to forget, looking up at the sky from our brief, limited scale, that the universe isn’t just some pretty lights drifting about in empty blackness. Things are exploding and dying, burning and freezing, moving quickly and slowly – the cosmos is replete with activity and danger. Most of the universe isn’t just uninhabitable, it’s actively hostile to life as we know it. And yet, without the black holes, the supernovas and the galactic collisions, without massive meteor impacts and breakaway comets, solar flares and deadly radiation – without all that, life probably wouldn’t exist at all. So read this book, and take a moment to appreciate how lucky we are to be here at all, all things considered….

————————————————-
“They say that even the brightest star won’t shine forever. But in fact, the brightest star would live the shortest amount of time. Feel free to extract whatever life lesson you want from that.”
– Phil Plait, Death from the Skies!
————————————————-

[1] 10 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000

Phil Plait on Wikipedia
Bad Astronomy blog
Death from the Skies! on Wikipedia
Death from the Skies! on Amazon.com

Leave a comment

Filed under apocalypse, astronomy, astrophysics, death, nonfiction, Phil Plait, science, survival, technology