Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Why is 100% efficient thermal insulator impossible?

  1. Jan 4, 2007 #1
    Somebody told me this and I have yet to figure out even if the statement is true or not.
  2. jcsd
  3. Jan 4, 2007 #2


    User Avatar
    Gold Member

    Because if it could be done, you could stop entropy. Which you can't.

    Even if you could stop conduction of heat, how would you stop a body from radiating heat?
  4. Jan 4, 2007 #3
    If u can stop entropy its lik saying u cud stop time.SO i guess its not possible
  5. Jan 5, 2007 #4


    User Avatar
    Gold Member

    Translation: If you can stop entropy it's like saying you could stop time, so I guess it's not possible.
  6. Jan 5, 2007 #5


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Stop entropy? What does that mean?
    If the question was, is there such a thing as a perfect insulator (i.e., has zero thermal conductivity), then the answer is "yes, a vacuum". Of course, you can't make a true vacuum, nor does a vacuum prevent radiation.
  7. Jan 5, 2007 #6


    User Avatar

    Staff: Mentor

    I like to look at such questions backwards: how could you make a perfect insulator? There are 3 types of heat transfer: conduction, convection, and radiation...

    As Gokul said, a vacuum will stop conduction and convection completely, but we can't make a perfect vacuum and even if you could, you'd have to support the structure with something. So you can't completely eliminate either conduction or convection in a device (though you can eliminate conduction between objects that aren't touching. But you can get either well above 99%.

    Stopping radiation is much more difficult than stopping either conduction or convection because it requires a perfect mirror that is perfect at all frequencies of radiation. And though you can get mirrors at in exess of 99% reflectance, the frequency range is limited.
  8. Jan 6, 2007 #7


    User Avatar
    Gold Member

    Since a vacuum doesn't prevent radiation, how does that make it a perfect insulator?
  9. Jan 6, 2007 #8


    User Avatar
    Science Advisor

    It doesn't because it does not prevent readiation as gokul said.

    But this perfect vacuum must exist a place farther away than light has reached since bing bang? Because if no radiation or mass have reached the point, nothing can be there.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?

Similar Discussions: Why is 100% efficient thermal insulator impossible?
  1. 100% Efficiency? (Replies: 11)