# Tag Info

74

Your intuition is good, but you're mixing up some quantum and classical phenomena. In classical (i.e. non-quantum) physics, a vacuum is a region of space with no matter. You can have electromagnetic fields in a vacuum, so long as the charges creating the fields are in a different region. By the same token you can have gravitational fields in a vacuum, ...

24

I don't understand the difference between the first and the second question, but the answer is "No, you don't need air for the clothes to dry". In fact, it will dry faster if in vacuum, because the water will start to boil in zero pressure, even if the temperature is not 100º C. In fact, at zero pressure, water cannot exist in liquid, but will evaporate if ...

17

The graviton is the hypothetical gauge boson associated with the gravitational field. I say hypothetical because it is far from clear whether gravity can be described by a quantum field theory, so it isn't clear whether gravitons are a useful description. In any case, you should not take the notion of virtual particles like the graviton too seriously. have ...

7

I think when you say "no air" you mean "no wind" In modern greek too "air" can mean "wind" and and also the content of the atmosphere. So if you hang clothes in the same sun but with no wind to supply convection, the clothes will try slower than when a wind is blowing, due to convection. Convection replaces the saturated air close to the clothes with ...

6

You are simply confusing vacuum with "nothingness", which is a philosophical concept. You can check the definition at wiki Vacuum is space that is devoid of matter. The word stems from the Latin adjective vacuus for "vacant" or "void". An approximation to such vacuum is a region with a gaseous pressure much less than atmospheric pressure.[1] ...

5

If we assume you are a sphere in space, at the same distance from the sun as Earth, then we can calculate the heat absorbed - and we can calculate how hot you need to be so heat in = heat out (assuming uniform surface temperature, and radiative heat transfer only). For this, we need the Stefan-Boltzmann expression for total emission at a given temperature: ...

5

In quantum mechanics, it's impossible to remove all the particles from a vacuum. A volume of space time that contains only photons and gravitons in thermal equilribium (or not) sounds like a perfectly good vacuum to me.

5

Internal friction in the metal of the bell eventually will bring the ringing vibrations to an end. The bell vibrates when it rings, making its molecules more energetic and creating heat. Bonding between the molecules of the bell resist the vibrations, and eventually the strength of the molecular bonds will create enough friction to bring the vibrations ...

4

Anything that "suspends" the bell - whether it be a bolt, a piece of string, or a magnetic field - is applying a force. When the bell vibrates, this vibration will be transmitted. This is because the force of a magnet is a function of position - you can only get magnetic attraction because of a divergence of the field, so if you move, the force changes and ...

4

No, because Haag's theorem states that there is no map between the free and interacting Hilbert spaces such that the fields and their commutation relations on one space are unitarily mapped onto the fields and their commutation relations on the other space. That is, the space of states of the interacting theory is as a representation of the commutation ...

4

The conductivity of the vacuum is not a very trivial issue. In fact, depending on how you look at it, it behaves in two different ways. Firstly, there is no retarding force on any charged particle with constant velocity in vacuum. To this extent, no extra work is required in maintaining a constant current through any surface in vacuum. In stark contrast ...

4

The colour of stars as observed by an observer on Earth varies just like the colour of our own Sun, depending on where in the sky the source is relative to the observer. However, the light of stars is generally too faint to notice this as clearly with the naked eye, because we cannot perceive colour for weak light sources.

3

No, Rayleigh scattering models the probability (and angle) of scattering as a function of wavelength and of the particle sizes. All wavelengths travel a long way but the path followed (scatter or nonscatter) varies. Since space is mostly "empty", there's little scattering. Beyond that, your understanding of stars is quite incomplete. THey do in fact have ...

3

Disclaimer before I get started: A perfect vacuum is impossible. As I answer your question, I will take your use of the word "vacuum" to mean "a chamber with an air pressure arbitrarily close to 0 Pa." When I use the word "vacuum" in my response, I mean the same. Your clothes don't need the air in order to dry, and in fact, will dry more quickly. ...

2

In theory, yes – it’s an effect called ‘cold welding’ by which the metallic bonds that hold atoms together in each object effectively ‘bridge the gap’ between them to create a single solid object. In practice, this rarely happens on Earth because most metals form a protective oxide layer where their surface is exposed to the atmosphere. Slight bumps and ...

2

Starlight, as emitted by a star, comes in a wide range of colours. For instance see the picture below. Now this is a picture, and pictures can often be tricky with their representation of colour, so you'll have to take my word for it that Betelgeuse does look significantly redder to the naked eye than say Vega until you get a chance to go look yourself on ...

2

No, in the very basic sense it is not a good conductor, because very high voltages are required to shoot them through. But yes it still is a conductor, because it allows the flow of current. Compare this to a diode, which similarly only allows current (in the same very basic sense) to flow if a certain voltage is applied. Such non linear behaviour exceeds ...

1

But can we really say that vacuum (..as in space) is a good conductor of electricity in a very basic sense? No, because vacuum is not a material object. The word conductor was meant for material bodies. It is not usually used to describe vacuum, because vacuum is not merely a different body from metal or dielectric, but it is a different concept - a ...

1

I know this question is technically already answered, but there were several things missing from the answers that I thought should be mentioned (I am writing a review paper comparing different regions of space so I had these numbers at hand already as well). The speed of sound in space has multiple meanings because space is not a vacuum (though the number ...

1

Suppose you have a box filled with water in a uniform fashion. Now if you try to stretch the box in the $z$-direction, say, while keeping the other dimensions constant, what is the energy required? Well if the water distribution remains uniform, you can approximate this by the Hookean law $E_\text{elastic} = \frac{1}{2}k(z-z_0)^2$. Note that the constant $k$ ...

1

What you're describing is theoretically possible, or at least there is no contradiction inherent in its conception any more than any other "pure" quantum state is: you simply need to prepare the pure quantum state which is the zero particle number observable eigenstate for all the quantum fields (electron, photon, ...). This of course corresponds to all the ...

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