. How are the suffixes of websites determined? For example, why is a particular website .com or .org or .in? — D, India
Although yours isn't a physics question, it's one that's interesting to me and easy to answer. The person who sets up the website gets to choose the domain. That's all there is to it. As long as the complete domain name hasn't already been registered, you can pay a fee and register it. For example, I chose to register this website as www.howeverythingworks.org because I feel more like an organization (of one person) than a commercial enterprise. I could have registered it as www.howeverythingworks.in, but that would imply I'm in India and I'm not. The only exception that I know of is .edu, which is restricted to educational institutions. I would not be allowed to register this website as www.howeverythingworks.edu.
Actually, I could have registered this website as www.howeverythingworks.com, but I would have had to purchase that domain name from someone else. It is registered to a cybersquatter—someone who registers a domain name in hopes of selling it at a profit to someone else. Cybersquatting was hugely popular during the internet bubble, when companies were paying vast amounts of money for particular domain names. But these days, who wants to pay thousands of dollars for a name? I'm totally happy to be www.howeverythingworks.org and I'll let someone else pay the big bucks to purchase www.howeverythingworks.com. In the meantime, that domain is just a link to advertising and an offer to sell the domain name.
. My boyfriend and I are having this debate on whether or not to squeeze the air out of a 2 liter bottle of Coke after opening it. He thinks it will keep the Coke carbonated longer and I disagree. Who is right? — TN, Ft. Collins, CO
Yours is actually a complicated question. After you open the soda, the CO2
dissolved in the soda is no longer in equilibrium with the gas above soda. When you cap the bottle, CO2
will gradually escape from the liquid until it forms a dense gas so that CO2
molecules from that gas return to the liquid solution as often as they leave the solution for the gas. In other words, the equilibrium between dissolved CO2
and gaseous CO2
has to be reestablished.
By shrinking the volume of gas over the soda, your boyfriend reduces the number of CO2 molecules that must enter the gas phase in order to reestablish that equilibrium. BUT, when dense gas develops in the squeezed bottle, the high pressure of that gas will reinflate the bottle to its original size. The benefits of shrinking the gas volume will thus be lost.
To succeed in keeping more of the CO2 molecules in solution, you have to make sure that the squeezed bottle stays squeeze. That's hard to do. You're probably better off pouring the soda gently into a smaller bottle, one that just barely holds all of the liquid. That smaller bottle won't expand as a dense gas of CO2 forms above the liquid soda and the soda will reestablish its equilibrium without losing too many of its dissolved CO2 molecules.
. When you traveling in a jet plane, why do objects on the ground look as though they are still or moving slowly? — K, India
When you watch something move, what you really notice is the change in the angle at which see you it. Nearby objects don't have to be traveling fast to make you turn your head quickly to watch them go by so you perceive them as moving rapidly. An object that is heading directly toward you or away from you doesn't appear to be moving nearly as quickly because its change in angle is much smaller.
When you watch a distant object move, you don't see it change angles quickly so you perceive it as moving relatively slowly. Take the moon for example: it is moving thousands of miles an hour yet you can't see it move at all. It's just so far away that you see no angular change. And when you look down from a high-flying jet, the distant ground is changing angles slowly and therefore looks like it's not moving fast.
. My eight year old daughter asked me, "If light is the fastest thing in the universe what is the second fastest thing in the universe?" — JPW, Lancaster, PA
Your daughter's question is a cute one. I like it because it highlights the distinction between the speed of light and all other speeds. The speed of light is unimaginably special in our universe. Strange though it may sound, even if light didn't exist there would still be the speed of light and it would still have the same value. The speed of light is part of the geometry of space-time and the fact that light travels at "the speed of light" is almost a cosmic afterthought. Gravity and the so-called "strong force" also travel at that speed.
OK, so there is actually a multi-way tie for first place in the speed rankings. Your daughter's question is what comes next? The actual answer is that it's a many-way tie between everything else. With enough energy, you can get anything moving at just under the speed of light, at least in principle. For example, subatomic particles such as electrons, protons, and even atomic nuclei are routinely accelerated to just under the speed of light in sophisticated machines around the world. The universe itself has natural accelerators that whip subatomic particles up until they are traveling so close to the speed of light that it's hard to tell that they aren't quite at the speed of light. Nonetheless, I assure you that they're not. The speed of light is so special that nothing that has any mass at all can possibly travel at the speed of light. Only the ephemeral non-massive particles such as light particles (photons), gravity particles (gravitons), and strong force particles (gluons) can actually travel at the speed of light. In fact, once photons, gravitons, and gluons begin to interact with matter, they don't travel at the speed of light either. It's sort of a guilt-by-association: as soon as these massless particles leave the essential emptiness of the vacuum and begin to interact with matter, even they can't travel at the speed of light anymore.
That said, I can still offer the likely second place finisher on the speed list. I'm going to skip over light, gravity, and the strong force traveling in extremely dilute matter because that's sort of cheating — if you take something that naturally travels at the speed of light and slow it down the very, very slightest bit, of course it will come ridiculously close to the speed of light. In real second place are almost certainly cosmic ray particles. These cosmic rays are actually subatomic particles that are accelerated to fantastic energies by natural processes in the cosmos. How such accelerators work is still largely a mystery but some of the cosmic ray particles that reach our atmosphere have truly astonishing energies — once in a while a single cosmic ray particle that is smaller than an atom will carry enough energy with it that it is capable of moving small ordinary objects around. Even if it carries the energy of a fly, that's a stupendous amount of energy for an atomic fragment. Those cosmic ray particles are traveling so close to the speed of light that it would be a photo-finish with light itself.
. I have a large commercial superconducting magnet and am looking for a high-value-added product or manufacturing process to pursue with it. Is there anything you have learned in your research that would be worth producing? — PT
As a general observation, the bottleneck in scientific research and technological innovation is almost always the ideas, not the equipment. Occasionally, a revolutionary piece of equipment comes on the scene and makes a whole raft of developments possible overnight. But a commercial superconducting magnet isn't revolutionary; you can buy one off the shelf. As a result, all the innovations that were waiting for magnets like that to become available were mopped up long ago and any new innovations will take new ideas.
Coming up with good ideas is hard work and if I had them, I'd have gotten hold of such a magnet myself. Although science is often taught as formulas and factoids, it's really about thinking and observing, and good ideas are nearly always more important than good equipment. Good ideas don't linger unstudied for long when commercial equipment is all it takes to pursue them.
. I have heard that we "know" the universe is expanding because everything is moving away from everything else. My question is: if this situation is like ink dots on a balloon, then we should be able to point to the direction of the universe's center. Which way is that center? - BS
The "ink dots on a balloon" idea provides the answer to your question. In that simple analogy, the ink dots represent stars and galaxies and the balloon's surface represents the universe. Inflating the balloon is then equivalent to having the universe expand. As the balloon inflates, the stars and galaxies drift apart so that an ant walking on the surface of the balloon would have to travel farther to go from one "star" to another. A similar situation exists in our real universe: everything is drifting farther apart.
The ant lives on the surface of the balloon, a two-dimensional world. The ant is unaware of the third dimension that you and I can see when we look at the balloon. The only directions that the ant can move in are along the balloon's surface. The ant can't point toward the center of the balloon because that's not along the surface that the ant perceives. To the ant, the balloon has no center. It lives in a continuous, homogeneous world, which has the weird property that if you walk far enough in any direction, you return to where you started.
Similarly, we see our universe as a three-dimensional world. If there are spatial dimensions beyond three, we are unaware of them. The only directions that we can move in are along the three dimensions of the universe that we perceive. The overall structure of the universe is still not fully understood, but let's suppose that the universe is a simple closed structure like the surface of a higher-dimensional balloon. In that case, we wouldn't be able to point to a center either because that center would exist in a dimension that we don't perceive. To us, the universe would be a continuous, homogeneous structure with that same weird property: if you traveled far enough in one direction, you'd return to where you started.
. If I knew the initial (exact) conditions of the throw of a die, could I throw a 6 with certainty? How does the Heisenberg principle affect my ability to control the outcome? — TW
In the classical view of the world, the view before the advent of quantum theory, nature seemed entirely deterministic and mechanical. If you knew exactly where every molecule and atom was and how fast it was moving, you could perfectly predict where it would be later on. In principle, this classical world would allow you to throw a 6 every time. Of course, you'd have to know everything about the air's motion, the thermal energy in the die, and even the pattern of light in the room. But the need for enormous amounts of information just means that controlling the dice will be incredibly hard, not that it will be impossible. For simple throws, you could probably get by without knowing all that much about the initial conditions. As the throws became more complicated and more sensitive to initial conditions, you'd have to know more and more.
However, quantum mechanics makes controlling the die truly impossible. The problem stems from the fact that position and velocity information are not fully defined at the same time in our quantum mechanical universe. In short, you can't know exactly where a die is and how fast it is moving at the same time. And that doesn't mean that you can't perform these measurements well. It means that the precise values don't exist together; they are limited by Heisenberg uncertainty. So quantum physics imposes a fundamental limit on how well you can know the initial conditions before your throw and it thus limits your ability to control the outcome of that throw. How much quantum physics affects your ability to throw a 6 depends on the complexity of the throw. If you just drop a die a few inches onto a table, you can probably get a 6 most of the time, despite quantum mechanics and without even knowing much classical information. But as you begin throwing the die farther, you'll begin to lose control of it because of quantum mechanics and uncertainty. In reality, you'll find classical physics so limiting that you'll probably never observe the quantum physics problem. Knowing everything about a system is already unrealistic, even in a classical universe. The problems arising from quantum mechanics are really just icing on the cake for this situation.
. How certain can I be that modern physics applies to distant places? Shouldn't I wait until reputable scientists have performed experiments way off in outer space? — JS
Fortunately, you don't have to wait that long. From astronomical observations, we are fairly certain that the laws of physics as we know them apply throughout the visible universe. It wouldn't take large changes in the physical laws to radically change the structures of atoms, molecules, stars, and galaxies. So the fact that the light and other particles we see coming from distant places is so similar to what we see coming from nearby sources is pretty strong evidence that the laws of physics don't change with distance. Also, the fact that the light we see from distant sources has been traveling for a long time means that the laws of physics don't seem to have changed much (if at all) with time, either. While there are theories that predict subtle but orderly changes in the laws of physics with time and location, effectively making those laws more complicated, no one seriously thinks that the laws of physics change radically and randomly from place to place in the Universe.
. If one metric ton of antimatter comes into contact with one metric ton of matter, how much energy would be released? — TC
Since the discovery of relativity, people have recognized that there is energy associated with rest mass and that the amount of that energy is given by Einstein's famous equation: E=mc2. However, the energy associated with rest mass is hard to release and only tiny fractions of it can be obtained through conventional means. Chemical reactions free only parts per billion of a material's rest mass as energy and even nuclear fission and fusion can release only about 1% of it. But when equal quantities of matter and antimatter collide, it's possible for 100% of their combined rest mass to become energy. Since two metric tons is 2000 kilograms and the speed of light is 300,000,000 meters/second, the energy in Einstein's formula is 1.8x1020 kilogram-meters2/second2 or 1.8x1020 joules. To give you an idea of how much energy that is, it could keep a 100-watt light bulb lit for 57 billion years.
. In your discussion of event horizons, you stated that light falls just like everything else. I thought that light does not speed up when falling but just gains energy—that it is blue-shifted. Conversely, when it rises in a gravitational field, it does not slow down but just loses energy—that it is red-shifted. Is that correct? — B
Yes. For very fundamental reasons, light can't change its speed in vacuum; it always travels at the so-called "speed of light." So light that is traveling straight downward toward a celestial object doesn't speed up; only its frequency and energy increase. But light that is traveling horizontally past a celestial object will bend in flight, just as a satellite will bend in flight as it passes the celestial object. This trajectory bending is a consequence of free fall. While the falling of light as it passes through a gravitational field is a little more complicated than for a normal satellite—the light's trajectory must be studied with fully relativistic equations of motion—both objects fall nonetheless.