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11

$begingroup$

What I've heard from books and other materials is that heat is nothing but the sum of the movement of molecules. So, as you all know, one common myth breaker was "Unlike in movies, you don't get frozen right away when you get thrown into space".

But the thing that bugs me is that things in the universe eventually cool down. How is that possible when there are no other things around to which the molecules can transfer their heat?

thermodynamics energy-conservation temperature equilibrium

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edited 1 hour ago

CJ Dennis

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dolcodolco

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$endgroup$

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  Molecules can give off electromagnetic radiation; their energy is transferred to the E.M. field itself. Eventually energy becomes evenly distributed, meaning that there can be no net gain or loss of energy. When that happens, objects will not cool off; entropy is maximised.
  $endgroup$
  – user234461
  14 hours ago
  

  
  
  
  


• 
  
  
  

  
  3
  

  
  
  
  
  
  

  
  $begingroup$
  The term you're looking for is Black-body radiation. Any object above 0K radiates heat away.
  $endgroup$
  – Tomáš Zato
  12 hours ago
  

  
  
  
  

add a comment
 | 

11

$begingroup$

What I've heard from books and other materials is that heat is nothing but the sum of the movement of molecules. So, as you all know, one common myth breaker was "Unlike in movies, you don't get frozen right away when you get thrown into space".

But the thing that bugs me is that things in the universe eventually cool down. How is that possible when there are no other things around to which the molecules can transfer their heat?

thermodynamics energy-conservation temperature equilibrium

share|cite|improve this question

edited 1 hour ago

CJ Dennis

47544 silver badges1313 bronze badges

asked yesterday

dolcodolco

16811 silver badge66 bronze badges

$endgroup$

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  $begingroup$
  Molecules can give off electromagnetic radiation; their energy is transferred to the E.M. field itself. Eventually energy becomes evenly distributed, meaning that there can be no net gain or loss of energy. When that happens, objects will not cool off; entropy is maximised.
  $endgroup$
  – user234461
  14 hours ago
  

  
  
  
  


• 
  
  
  

  
  3
  

  
  
  
  
  
  

  
  $begingroup$
  The term you're looking for is Black-body radiation. Any object above 0K radiates heat away.
  $endgroup$
  – Tomáš Zato
  12 hours ago
  

  
  
  
  

add a comment
 | 

$begingroup$

What I've heard from books and other materials is that heat is nothing but the sum of the movement of molecules. So, as you all know, one common myth breaker was "Unlike in movies, you don't get frozen right away when you get thrown into space".

But the thing that bugs me is that things in the universe eventually cool down. How is that possible when there are no other things around to which the molecules can transfer their heat?

thermodynamics energy-conservation temperature equilibrium

share|cite|improve this question

edited 1 hour ago

CJ Dennis

47544 silver badges1313 bronze badges

asked yesterday

dolcodolco

16811 silver badge66 bronze badges

$endgroup$

share|cite|improve this question

edited 1 hour ago

CJ Dennis

47544 silver badges1313 bronze badges

asked yesterday

dolcodolco

16811 silver badge66 bronze badges

share|cite|improve this question

edited 1 hour ago

CJ Dennis

47544 silver badges1313 bronze badges

asked yesterday

dolcodolco

16811 silver badge66 bronze badges

edited 1 hour ago

CJ Dennis

47544 silver badges1313 bronze badges

edited 1 hour ago

CJ Dennis

47544 silver badges1313 bronze badges

asked yesterday

dolcodolco

16811 silver badge66 bronze badges

asked yesterday

dolcodolco

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2 Answers
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27

$begingroup$

You exchange heat with the objects around you.

If the objects around you are hotter than you, you'll heat up.

If the objects around you are cooler than you (neglecting the heat you're generating due to metabolic processes), you'll cool off.

In space, the objects around you (mostly interstellar medium) is cooler than you so you radiate more heat away from you into them than they radiate toward you.

If you were thrown out into space, but very near a star, you might receive more heat from the star more than you could radiate away into space, and you would heat up rather than cooling down.

But the thing which bugs me is that things in the Universe, eventually cool off, and how is that possible, when there's no other things around, to which the molecules transfer their heat?

There are three main heat transfer mechanisms.

conduction is transfer by direct contact between two bodies, or through a body with a temperature gradient across it.

convection is transfer by the flow of a fluid (liquid or gas).

radiation is transfer by the exchange of electromagnetic radiation.

Heat transfer by radiation doesn't require any physical contact between two bodies or any material medium surrounding a body. Radiation is the main heat transfer mechanism for a body floating in space.

share|cite|improve this answer

edited yesterday

answered yesterday

The PhotonThe Photon

11.9k11 gold badge2323 silver badges4040 bronze badges

$endgroup$

• 
  
  
  

  
  10
  

  
  
  
  
  
  

  
  $begingroup$
  It should be noted that radiation is much less efficient than the other two, which is why space suits, the Space Shuttle and the ISS need big radiators or other cooling systems. This is a bit counter-intuitive given that "everybody knows" space is cold. The reason is that space is also very empty, so there is nothing to conduct to or convect with.
  $endgroup$
  – Jörg W Mittag
  16 hours ago
  

  
  
  
  


• 
  
  
  

  
  5
  

  
  
  
  
  
  

  
  $begingroup$
  @JörgWMittag AFAIK the space suits aren't even big enough for that - they use disposable coolant, and when you run out (or the fans break down), you die of heatstroke in short order.
  $endgroup$
  – Luaan
  15 hours ago
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  $begingroup$
  @JörgWMittag: What do you mean exactly, "radiation is much less efficient than the other two"? It depends on temperature levels and what's between the two bodies. I hear convection and conduction aren't very efficient to transfer thermal energy between the Sun and Earth.
  $endgroup$
  – Eric Duminil
  13 hours ago
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  $begingroup$
  @JörgWMittag very well put and a great real world example is water vs. air and the human body. It's relatively comfortable to get out in 72F/22C air but to get into water of that temperature is extremely cold!
  $endgroup$
  – jwh20
  13 hours ago
  

  
  
  
  


• 
  
  
  

  
  3
  

  
  
  
  
  
  

  
  $begingroup$
  Most importantly for the question, if there's no object around you, your body radiates infrared anyway, not caring if the radiation will land on the Earth, the Moon, Alpha Centauri or nothing at all.
  $endgroup$
  – Eric Duminil
  13 hours ago
  

  
  
  
  

 | 
show 1 more comment

2

$begingroup$

Everything that is not 0 Kelvin radiates electromagnetic energy. In vacuum, this is the only relevant form of heat transfer. The hotter you are, the more you energy you radiate (I believe the relevant equation is given here).

So, the question whether you cool off or heat up in space depends on whether you absorbs more electromagnetic radiation than you give away. So, for instance, if you are orbiting Earth in plain sunlight, you may actually warm up, because there is lot of electromagnetic energy coming from the sun (much of it as visible light).

But if you are in the shadow of the Earth, the amount of energy that comes from night side of Earth and the general direction of the outer space is very low compared the the amount of energy you radiate away at 37ºC, so you cool off and eventually freeze.

share|cite|improve this answer

answered 11 hours ago

lvellalvella

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$endgroup$

add a comment
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27

$begingroup$

You exchange heat with the objects around you.

If the objects around you are hotter than you, you'll heat up.

If the objects around you are cooler than you (neglecting the heat you're generating due to metabolic processes), you'll cool off.

In space, the objects around you (mostly interstellar medium) is cooler than you so you radiate more heat away from you into them than they radiate toward you.

If you were thrown out into space, but very near a star, you might receive more heat from the star more than you could radiate away into space, and you would heat up rather than cooling down.

But the thing which bugs me is that things in the Universe, eventually cool off, and how is that possible, when there's no other things around, to which the molecules transfer their heat?

There are three main heat transfer mechanisms.

conduction is transfer by direct contact between two bodies, or through a body with a temperature gradient across it.

convection is transfer by the flow of a fluid (liquid or gas).

radiation is transfer by the exchange of electromagnetic radiation.

Heat transfer by radiation doesn't require any physical contact between two bodies or any material medium surrounding a body. Radiation is the main heat transfer mechanism for a body floating in space.

share|cite|improve this answer

edited yesterday

answered yesterday

The PhotonThe Photon

11.9k11 gold badge2323 silver badges4040 bronze badges

$endgroup$

• 
  
  
  

  
  10
  

  
  
  
  
  
  

  
  $begingroup$
  It should be noted that radiation is much less efficient than the other two, which is why space suits, the Space Shuttle and the ISS need big radiators or other cooling systems. This is a bit counter-intuitive given that "everybody knows" space is cold. The reason is that space is also very empty, so there is nothing to conduct to or convect with.
  $endgroup$
  – Jörg W Mittag
  16 hours ago
  

  
  
  
  


• 
  
  
  

  
  5
  

  
  
  
  
  
  

  
  $begingroup$
  @JörgWMittag AFAIK the space suits aren't even big enough for that - they use disposable coolant, and when you run out (or the fans break down), you die of heatstroke in short order.
  $endgroup$
  – Luaan
  15 hours ago
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  $begingroup$
  @JörgWMittag: What do you mean exactly, "radiation is much less efficient than the other two"? It depends on temperature levels and what's between the two bodies. I hear convection and conduction aren't very efficient to transfer thermal energy between the Sun and Earth.
  $endgroup$
  – Eric Duminil
  13 hours ago
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  $begingroup$
  @JörgWMittag very well put and a great real world example is water vs. air and the human body. It's relatively comfortable to get out in 72F/22C air but to get into water of that temperature is extremely cold!
  $endgroup$
  – jwh20
  13 hours ago
  

  
  
  
  


• 
  
  
  

  
  3
  

  
  
  
  
  
  

  
  $begingroup$
  Most importantly for the question, if there's no object around you, your body radiates infrared anyway, not caring if the radiation will land on the Earth, the Moon, Alpha Centauri or nothing at all.
  $endgroup$
  – Eric Duminil
  13 hours ago
  

  
  
  
  

 | 
show 1 more comment

27

$begingroup$

You exchange heat with the objects around you.

If the objects around you are hotter than you, you'll heat up.

If the objects around you are cooler than you (neglecting the heat you're generating due to metabolic processes), you'll cool off.

In space, the objects around you (mostly interstellar medium) is cooler than you so you radiate more heat away from you into them than they radiate toward you.

If you were thrown out into space, but very near a star, you might receive more heat from the star more than you could radiate away into space, and you would heat up rather than cooling down.

But the thing which bugs me is that things in the Universe, eventually cool off, and how is that possible, when there's no other things around, to which the molecules transfer their heat?

There are three main heat transfer mechanisms.

conduction is transfer by direct contact between two bodies, or through a body with a temperature gradient across it.

convection is transfer by the flow of a fluid (liquid or gas).

radiation is transfer by the exchange of electromagnetic radiation.

Heat transfer by radiation doesn't require any physical contact between two bodies or any material medium surrounding a body. Radiation is the main heat transfer mechanism for a body floating in space.

share|cite|improve this answer

edited yesterday

answered yesterday

The PhotonThe Photon

11.9k11 gold badge2323 silver badges4040 bronze badges

$endgroup$

• 
  
  
  

  
  10
  

  
  
  
  
  
  

  
  $begingroup$
  It should be noted that radiation is much less efficient than the other two, which is why space suits, the Space Shuttle and the ISS need big radiators or other cooling systems. This is a bit counter-intuitive given that "everybody knows" space is cold. The reason is that space is also very empty, so there is nothing to conduct to or convect with.
  $endgroup$
  – Jörg W Mittag
  16 hours ago
  

  
  
  
  


• 
  
  
  

  
  5
  

  
  
  
  
  
  

  
  $begingroup$
  @JörgWMittag AFAIK the space suits aren't even big enough for that - they use disposable coolant, and when you run out (or the fans break down), you die of heatstroke in short order.
  $endgroup$
  – Luaan
  15 hours ago
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  $begingroup$
  @JörgWMittag: What do you mean exactly, "radiation is much less efficient than the other two"? It depends on temperature levels and what's between the two bodies. I hear convection and conduction aren't very efficient to transfer thermal energy between the Sun and Earth.
  $endgroup$
  – Eric Duminil
  13 hours ago
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  $begingroup$
  @JörgWMittag very well put and a great real world example is water vs. air and the human body. It's relatively comfortable to get out in 72F/22C air but to get into water of that temperature is extremely cold!
  $endgroup$
  – jwh20
  13 hours ago
  

  
  
  
  


• 
  
  
  

  
  3
  

  
  
  
  
  
  

  
  $begingroup$
  Most importantly for the question, if there's no object around you, your body radiates infrared anyway, not caring if the radiation will land on the Earth, the Moon, Alpha Centauri or nothing at all.
  $endgroup$
  – Eric Duminil
  13 hours ago
  

  
  
  
  

 | 
show 1 more comment

$begingroup$

You exchange heat with the objects around you.

If the objects around you are hotter than you, you'll heat up.

If the objects around you are cooler than you (neglecting the heat you're generating due to metabolic processes), you'll cool off.

In space, the objects around you (mostly interstellar medium) is cooler than you so you radiate more heat away from you into them than they radiate toward you.

If you were thrown out into space, but very near a star, you might receive more heat from the star more than you could radiate away into space, and you would heat up rather than cooling down.

But the thing which bugs me is that things in the Universe, eventually cool off, and how is that possible, when there's no other things around, to which the molecules transfer their heat?

There are three main heat transfer mechanisms.

conduction is transfer by direct contact between two bodies, or through a body with a temperature gradient across it.

convection is transfer by the flow of a fluid (liquid or gas).

radiation is transfer by the exchange of electromagnetic radiation.

Heat transfer by radiation doesn't require any physical contact between two bodies or any material medium surrounding a body. Radiation is the main heat transfer mechanism for a body floating in space.

share|cite|improve this answer

edited yesterday

answered yesterday

The PhotonThe Photon

11.9k11 gold badge2323 silver badges4040 bronze badges

$endgroup$

share|cite|improve this answer

edited yesterday

answered yesterday

The PhotonThe Photon

11.9k11 gold badge2323 silver badges4040 bronze badges

answered yesterday

The PhotonThe Photon

11.9k11 gold badge2323 silver badges4040 bronze badges

answered yesterday

The PhotonThe Photon

11.9k11 gold badge2323 silver badges4040 bronze badges

2

$begingroup$

Everything that is not 0 Kelvin radiates electromagnetic energy. In vacuum, this is the only relevant form of heat transfer. The hotter you are, the more you energy you radiate (I believe the relevant equation is given here).

So, the question whether you cool off or heat up in space depends on whether you absorbs more electromagnetic radiation than you give away. So, for instance, if you are orbiting Earth in plain sunlight, you may actually warm up, because there is lot of electromagnetic energy coming from the sun (much of it as visible light).

But if you are in the shadow of the Earth, the amount of energy that comes from night side of Earth and the general direction of the outer space is very low compared the the amount of energy you radiate away at 37ºC, so you cool off and eventually freeze.

share|cite|improve this answer

answered 11 hours ago

lvellalvella

47022 silver badges1515 bronze badges

$endgroup$

add a comment
 | 

2

$begingroup$

Everything that is not 0 Kelvin radiates electromagnetic energy. In vacuum, this is the only relevant form of heat transfer. The hotter you are, the more you energy you radiate (I believe the relevant equation is given here).

So, the question whether you cool off or heat up in space depends on whether you absorbs more electromagnetic radiation than you give away. So, for instance, if you are orbiting Earth in plain sunlight, you may actually warm up, because there is lot of electromagnetic energy coming from the sun (much of it as visible light).

But if you are in the shadow of the Earth, the amount of energy that comes from night side of Earth and the general direction of the outer space is very low compared the the amount of energy you radiate away at 37ºC, so you cool off and eventually freeze.

share|cite|improve this answer

answered 11 hours ago

lvellalvella

47022 silver badges1515 bronze badges

$endgroup$

add a comment
 | 

$begingroup$

Everything that is not 0 Kelvin radiates electromagnetic energy. In vacuum, this is the only relevant form of heat transfer. The hotter you are, the more you energy you radiate (I believe the relevant equation is given here).

So, the question whether you cool off or heat up in space depends on whether you absorbs more electromagnetic radiation than you give away. So, for instance, if you are orbiting Earth in plain sunlight, you may actually warm up, because there is lot of electromagnetic energy coming from the sun (much of it as visible light).

But if you are in the shadow of the Earth, the amount of energy that comes from night side of Earth and the general direction of the outer space is very low compared the the amount of energy you radiate away at 37ºC, so you cool off and eventually freeze.

share|cite|improve this answer

answered 11 hours ago

lvellalvella

47022 silver badges1515 bronze badges

$endgroup$

share|cite|improve this answer

answered 11 hours ago

lvellalvella

47022 silver badges1515 bronze badges

answered 11 hours ago

lvellalvella

47022 silver badges1515 bronze badges

answered 11 hours ago

lvellalvella

47022 silver badges1515 bronze badges