# Tagged Questions

The near-vacuum extending between the planets and stars, containing small amounts of gas and dust. Also called outer space to refer to the physical universe beyond the Earth's atmosphere.

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### “Artificial gravity” on a rotating space stations

There have been a lot of sci-fi shows recently using the "rotating space station" explanation for gravity on space stations. After watching these videos: http://www.youtube.com/watch?v=49JwbrXcPjc&...
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### What is the largest sphere of liquid water that could exist in space held together under it's own gravity? [duplicate]

What is the largest theoretical sphere of liquid water that could exist in space held together under it's own gravity? I've always wondered if a planet the size of earth could exist as a single volume ...
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### Consequences of destroying a space elevator

Suppose there is a fully functional space elevator built on Earth. The base is attached to coordinates $(\lambda, \varphi) = (0,0)$ e.g., on the equator on the zero-meridian. What would happen ...
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### How does blood/saliva boil in outer space?

Why would the blood boil? Is it because of the temperature or pressure? Because I really can't figure it out. I thought space didn't have a temperature above freezing unless close to a star or the sun....
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### Equation of the saddle-like surface with constant negative curvature?

What is the equation for the saddle-like 2d surface (embeded in 3d Euclidean space with cartesian coordinates x, y and z) with constant negative curvature frequently used to illustrate open universe (...
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### “Space” in General Relativity and “vacuum” in Standard Model, is it the same thing?

And expansion of space is equal to expansion of vacuum?
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### An electromagnetic space elevator?

If you surround the equator with a continuous Niobium Tin superconductor ring, and ran somewhere near but less than the maximum current density through, the magnetic field of the Earth would support ...
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### How would a huge ball of air look in space from outside and from inside?

If you replaced the Earth (except the atmosphere) with air and kept the pressure linear to the center (of the now non-existing Earth) while ignoring the effects this would have on gravity and leaving ...
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### How fast until you feel wind in space? [duplicate]

I couldn't find this question asked anywhere else, so I thought I would ask it here: does anyone know how fast you would have to be traveling in space to feel 'wind' from the particles in front of you?...
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### Is a semi-Euclidean space possible?

Does exists a geometry (3d for example) which is Euclidean in 2 dimensions (x and y coordinates) and non-Euclidean when the third dimension (z) is taken into account? In other words a space where it ...
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### Definition of “direction”

Is there an actual definition of "direction" (that is, spatial direction) in physics, or is it just one of those terms that's left undefined? In physics textbooks it's always just taken for granted ...
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### How to measure the effects of the rotation around the Sun?

It is well know that we can measure the spinning of the Earth with a Foucault pendulum. But, is there a similar experiment for the rotation of the Earth around the Sun? I would like to know if we ...
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### Does space have a “radiation pressure” caused by subatomic particles?

If space is not actually a void, then there's something shooting around in it, I'm guessing a lot like molecules in a gas. Could we apply a $(PV/T = k)$ -like gas law to it. Obviously we're not ...
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### What properties do you need for building a tower?

When I was a boy I used to daydream about building a tower so tall that the top of it would stick out of the top of Earth's atmosphere project into near space. There would perhaps be a zero gravity ...
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### In a spaceship, if a vessel suddently stops will an object inside the vessel keep going?

My question is a 2 part question. First if a vessel in space is going very fast and suddently stops (maybe it is not possible but that is not the point) will things/humans inside the vessel keep ...
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### what are dimensions?

First, discrete examples. In a computer screen I can specify any "2D" point with just one single number (pixel order starting count from first at upper left, and going on, left2right and up2down ...
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### Explaining lightyear to non technical people

I need to explain the concept of a light-year to a non technical audience. Actually a presentation about planets and galaxies. It is quite difficult (for them) to comprehend the speed of light itself ,...
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### How does sound travel in space?

In relation to this question: How can a black hole produce sound? Which notes that the hole "produces" sound. The top answer states that: What you think of as the hard vacuum of outer space ...
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### Microgravity: how powerful is an astronaut

In 2008, NASA astronaut Clayton Anderson tossed a 635-kg tank of ammonia coolant overboard from the International Space Station (ISS). Subsequently the tank burned up in earth atmosphere as planned. ...
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### What is an “Idea” in terms of time space and matter? [closed]

If the physical world we know is made of matter stretched in time and space and some forces affecting it, what would be an Idea, pure Information or something similar. Does those things don't exist ...
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### What exactly happens to an exposed human body in space?

I know that space is a vacuum, has no air, and is very, very cold. From what I have seen in movies and TV shows when a space suit is exposed the oxygen will escape like a visible gas and the person ...
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### Can an elliptical orbit take the same time as a circular obit?

In the picture below you can see two orbits of potential pbjects. The main aspect of the orbits is that they have a collision point at the maximum of the elliptical orbit. My question is, could the ...
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### Sum total distance of electrons on a spherical surface

What is the sum total distance between every possible pair of point charges when there are n point charges on a spherical surface? All point charges can only and are located on the infinitesimal ...
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### Object docking in Space

How do objects dock in space? There's a recent piece of news that Keppler would dock to the ISS sometime this week. I want to know the operational aspects of it - considering the velocity of the ...
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### Nothing vs. empty space

This question quotes Hawking saying: [...] you enter a world where conjuring something out of nothing is possible (at least, for a short while). That's because at this scale particles, such as ...
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### How hot would space feel?

I read that the temperature of the space around the earth can vary greatly depending on whether or not it is in direct sunlight. Space, however, is not very dense, so I imagine that heat would not ...
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### What is an extreme deep field image (XDF) and how is it captured?

NASA recently took this Extreme Deep Field image (XDF) that is the area of only small fraction of the dia of moon and contains 5,500 galaxies. Nasa says this was capture by extreme long exposures so ...
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### Will stars disappear from the sky when their particle horizon is outside the event horizon

Given that the universe is expanding at an accelerated rate, will there be a point where stars visible in the night sky will simply disappear from view when their particle horizon is outside the event ...
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### Is dark energy around a black hole locally curved?

The repartition of dark energy in the vacuum is homogeneous all over the universe. The diagram below represents space with a black hole in the middle. The square is divided in small unit squares. If ...
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### How much time has passed for Voyager I since it left the Earth, 34 years ago?

34 years have passed since Voyager I took off and it's just crossing the solar system, being approximately at 16.4 light-hours away. How much time have passed for itself, though?
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### Why model space with real numbers?

Are there any good papers discussing why we use $\mathbb{R}^{3}$as a model for space? More specifically are there any that explain why we don't use other number systems such as extensions of the real ...
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### Is rocket propellant meaningfully a form of “space junk”

I imagine that most people are familiar with the concept of space junk (or space debris), which is a hazard to space exploration that grows with every item that humans leave in space. Wikipedia lists ...
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### 2 different density liquids in space

Lets say you are in deep space with basically zero gravity. You have a ball of water floating in front of you. If you carefully injected that ball with a syringe filled with vegetable oil, what ...
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### Oberth Effect in deep space

Does the Oberth effect only apply when in orbit of a planet or would a rocket generate more and more thrust (if kept on) even in deep space? Wikipedia explains that the faster the rocket goes, the ...
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### Can structural trusses in centrifuges be helpful at all?

Imagine a rotating space station for the purpose of creating artificial gravity. Generally, such a space station is portrayed as a ring or a cylinder. Images of these space stations often have lines ...
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### What is the voltage difference between the Moon and the Earth?

The Moon and Earth are approximately spherical conductive balls and the Earth has a self-capacitance of around 710uF. Is there ever a significant potential difference in the Earth-Moon system? Is ...
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### The most stable metal for radioactive environment

Could you suggest which metal/alloy shows the least activation & better long-term stability for space (LEO, inside Van allen belts, deep space) applications? Or stability of construction ...
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### Can a huge gravitational force cause visible distortions on an object

In space, would it be possible to have an object generating such a huge gravitational force so it would be possible for an observer (not affected directly by gravitational force and the space time ...
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### Why is everything floating in space so cold?

Of course there is pretty hot stuff too. For example Suns. But isn't the vacuum of space the perfect containment for heat? And shouldn't the rare collision with particles even heat up an object that ...
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### What's wrong with this reactionless drive?

I think this is analogues for the Woodward effect, but macroscopic: We assume a spacecraft consisting of a broomstick, a donut and lots of gear for storing and transfering mechanical energy. Take the ...
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### how does international space station change its orientation?

In what way does the rotating gyroscope help in changing the orientation of the international space station in space ? Is there any other way to change the the orientation of ISS ?
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### Under what practical conditions would Earth's atmosphere be a dilatant?

I have read and heard in many places that when the astronauts of Apollo were coming back to Earth, they had to determine the best angle of attack to re-enter the atmosphere. This is usually indicated ...
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### How do NASA's Curiosity determine the elemental composition of Mars using spectrometer?

From this article on hindustantimes.com - Curiosity sends data about Martian surface: The resultant flash of glowing plasma is viewed by the system’s 4.3-inch aperture telescope, which sends the ...
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### Is there an analogue of configuration space in quantum mechanics?

In classical mechanics coordinates are something a bit secondary. Having a configuration space $Q$ (manifold), coordinates enter as a mapping to $\mathbb R^n$, $q_i : Q \to \mathbb R$. The primary ...
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### Would Titan moon blow up if you light a match?

Given that the atmosphere of Titan is mostly methane, and from a comment on this TED talk... Would it blow up from a lighted match-stick? Seems like it's at least plausible. But, wouldn't the lack of ...
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### How do we know that the CMBR is the oldest light?

How do we know that the CMBR is the oldest light which we can see? Is it based just on the facts 1.that waves redshift with expanding space, and 2.predictions of the big bang theory; Or is there a way ...
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### From how deep into space can a human “skydive” back to earth? [duplicate]

Possible Duplicate: From how high could have Felix Baumgartner jumped without disintegrating like a shooting star? If a human can skydive from an altitude of 24 miles (39 km), and a satellite ...
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### Visualizing Electromagnetic Waves in 3D Space [closed]

I did one module of physics for my GCSE one year ago which taught me about transverse EM waves & the EM spectrum, but since then, I do not understand how a wave would move in 3D space. Can someone ...