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41

I'm not going to address the production mechanism,1 just the nature of the "sound" in this case. What you think of as the hard vacuum of outer space could just as well be seen as a very, very, very diffuse, somewhat ionized gas. That gas can support sound waves as long as the wavelength is considerably longer than the mean free path of the atoms on the ...


39

It's not a mechanism so much as a misconception of the nature of space (and its relationship to time): at low velocities, everything looks linear and Euclidean so we assume it is, but in reality it is not (as can be determined by appropriate experiments). It's kind of like asking by what mechanism you can reach something to your west by traveling east: if ...


38

In space you don't just "go somewhere". You have to match orbits, while not wasting too much fuel. If you're in a low circular orbit, and you want to get to a high circular orbit, it takes two tangential burns, one to elongate your orbit into an ellipse, and another at the high point of the ellipse to make it circular again. This is called a Hohman ...


32

Ok David asked me to bring the rain. Here we go. Indeed it is very feesible and very efficient to use an electromagnetic accelerator to launch something into orbit, but first a look at our alternative: Space Elevator: we don't have the tech Rockets: You spend most of the energy carrying the fuel, and the machinery is complicated, dangerous, and it cannot ...


31

The Sun isn't "made of fire". It's made mostly of hydrogen and helium. Its heat and light come from nuclear fusion, a very different process that doesn't require oxygen. Ordinary fire is a chemical reaction; fusion merges hydrogen nuclei into helium, and produces much more energy. (Other nuclear reactions are possible.) As for rockets, they carry both ...


30

As the other guys have already covered most of the topic, I'd like to quote some things. Light can't escape only from the inside of event horizon because it has already fallen into it. But after reading the article now, we could indicate some points. The article specifically says a "supermassive blackhole". They're a way too bulk in size when compared to ...


26

The relevant Science summary is "Radio Bursts, Origin Unknown" by Cordes, abstract here. Briefly, it notes that a burst of radio waves will undergo dispersion in the interstellar and intergalactic medium (ISM and IGM), the amount of which is indicative of how much matter the signal has passed through. Some further background not given in that summary: In ...


25

The gas molecules in your bottle of air aren't just sitting still, they're moving around in random directions. From memory, the speed of oxygen and nitrogen molecules at room temperature is around 500 meters per second. When the bottle is closed, the air molecules hit the walls and lid of the bottle and bounce back, so the air stays in the bottle. If you ...


24

There have actually been cases of (accidental!) exposure to near-vacuum conditions. Real life does not conform to what you see in the movies. (Well, it depends on the movie; Dave Bowman's exposure to vacuum in 2001 was pretty accurate.) Long-term exposure, of course, is deadly, but you could recover from an exposure of, say, 15-30 seconds. You don't ...


21

Ignoring the "no gravity" part of your question - there is, it's 1/6th that of the Earth, the flag looks like it's "waving" because the horizontal pole that runs along the top of the flag got stuck part way out. This meant that the flag didn't "unfurl" fully and is hanging like a curtain rather than being stretched flat as was the original intention. The ...


19

Suppose you move a small distance $\vec{dr}$ = ($dx$, $dy$, $dz$) and you take a time $dt$ to do it. Pre-special relativity you could say three things. Firstly the distance moved is given by: $$ dr^2 = dx^2 + dy^2 + dz^2 $$ (i.e. just Pythagorus' theorem) and secondly the time $dt$ was not related to the distance i.e. you could move at any velocity. Lastly ...


18

At constant 1 g acceleration half-way through, then constant 1 g deceleration the remaining half, it takes 7 years in rocket time, 38 years in Earth time: http://www.cthreepo.com/lab/math1.shtml Scroll down to Long Relativistic Journeys and enter your data. To the Andromeda Galaxy (2.5 mil ly) it's 29 years in rocket time! :)


17

For the sorts of vehicles we're used to, like cars and aeroplanes, there are two contributions to drag. There's the drag caused by turbulence, and the drag caused by the effort of pushing the air out of the way. The streamlining in cars and aeroplanes is designed to reduce the drag due to turbulence. The effort of pushing the air out of the way is basically ...


16

It's a great way to get gyroscopic stability. NASA has been using this technique for a long time. For instance, the Pioneer spacecraft used this method. Another example is the Juno spacecraft as well. I hope that answers your question sufficiently.


16

Strictly speaking vacuum is the state of lowest energy. That means no matter or radiation (photons or any other particles). Note that space is not a perfect vacuum. Also note that, technically, a gas of planets and comets etc. has a pressure (there is usually little reason to care about it though). There is also radiation pressure due to the photons. ...


15

It will diffuse into space. Space is a near-perfect vacuum—its pressure is nearly zero and it has extremely little matter (in the empty parts, at any rate). On the other hand, your bottle has a relatively high pressure. When you remove the barrier (by opening the cap), the air naturally flows to the region of low pressure. Once there, it creates a ...


15

The right way to think about this is geometry--- but the geometry mixes up space and time. I wrote some answers about this here: Einstein's postulates <==> Minkowski space. (In layman's terms) and here: Help Me Gain an Intuitive Understanding of Lorentz Contraction and if you read these first, you can easily understand the effect. The Lorentz ...


14

A brief history of the misapplication of magnetohydrodynamics to the analysis of the solar wind: 1959: Soviet satellite Luna 1 directly observed the solar wind for the first time and measured its strength. http://en.wikipedia.org/wiki/Luna_1 So as of 1959, by direct experimental observation, it was known that the heliopause was at least the radius of the ...


13

When you take the lid off, all the molecules that would otherwise hit it escape since there is nothing to hold them back. Although the molecules are going at a typical thermal velocity of roughly 500 m/s, the mean free path of molecules in air is about 70 nm and it therefore takes some time for molecules near the bottom of the bottle to "find out" that the ...


12

First of all, it is an elementary misconception that there would be a "zero gravity" environment in a tower that would only reach the top of the atmosphere. Most of the air molecules exist at a height smaller than 10 kilometers - and above 100 kilometers from the Earth's surface, the air is so diluted that it becomes undetectable. At the height of 10 ...


12

Two points that may help Think about what is required in order to accelerate. You have to throw something overboard.1 However your engine works you will eventually run out of fuel and at that point you are done accelerating. There is an exception to the "run out of fuel" claim and a possible loophole. The exception is a photon drive: just point a laser ...


12

When the cosmonaut sneezed they would start moving, and rotating, in the opposite direction, but when the sneeze hit their faceplate (ugh!) this would stop the motion. The net result is that the velocity of the cosmonaut would not have changed, but their position and angle would have. According to Wikipedia a typical breath is 500cm$^3$ and a sneeze ...


12

I think what would happen is that any water molecule with enough energy to escape the surface tension would escape. Because there is no air to provide the water molecule with a way of turning round and going back in, it would permanently leave. This means that the highest energy molecules would selectively evaporate, lowering the average energy of the ...


11

Something like this, along with the associated article on Wikipedia, might help: And if you "learn by doing" and are willing to have a bit of fun while you develop a sense of the "map" there's a boardgame (of all things) that treats this topic fairly accurately (at least if what you're looking for is some intuition about how the $\Delta\text{V}$ map feels ...


11

According to Universe Today, for the intergalactic medium they state a figure of only one hydrogen atom per cubic meter. As a point of comparison, the University of California, San Diego quotes an interstellar density of 1 atom per cubic centimeter. As to why it is important, all this material has photoionization effects on observations. Even though it is ...


11

1) Most materials you use in everyday life contain far more moisture than you might believe. This is a major reason materials meant to be exposed to space are specially designed and tested. In a general vacuum, most fabrics and many plastic will outgas - all of the absorbed moisture and oils will work their way to the surface and boil off - which is a major ...


10

Actually no, because even in a perfect vacuum the object will emit gravity waves and slowly spiral into the planet. However this is a somewhat pedantic answer since for all but very high masses orbiting very close to each other, the gravity wave radiation is so small that the orbit would be stable on timescales far longer than the age of the universe. ...


10

Turn on your rocket engines or configure your space craft into a rotating cylinder.


10

Dear GJ, "vacuum" and "empty space" is always the same thing, but one must always be careful what these two synonymous terms mean. General relativity implies that the only "information" that the vacuum carries at each point is the so-called "metric tensor" - a set of numbers that allow one to calculate the distance between any two nearby points. This is ...


10

I am going to speculate on a production mechanism to complement @dmckee's answer. It is true that light cannot escape from a black hole, except it can lose energy through Hawking radiation. Suppose the black hole oscillates,vibrates, i.e. within it compression waves exist this would of course be another way of losing energy. This because the radius of the ...



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