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B Would current flow in a vacuum like space

  1. Mar 25, 2017 #1
    Would lightning work in space? I think it would but you wouldn't be able to see it?

    Let's say I have some sort of device that creates a lightning bolt, if I shot it at a watermelon in a vacuum or another target would it hit the target, or nothing happen because of the vacuum???
  2. jcsd
  3. Mar 25, 2017 #2
    Vacuum acts as an insulator but eventually if voltage is high enough there will be lightning. At least that's what I've always understood.
  4. Mar 25, 2017 #3


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    I think it would work, because old fashioned TV's had electrons flowing in a vacuum.
  5. Mar 25, 2017 #4
    All particles with electric charge have mass. If a volume of space contains some moving electrons, is it still vacuum?
  6. Mar 25, 2017 #5


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    HI Shark1j
    welcome to PF :smile: ... you initial conclusion is correct, tho you may not be aware of the reason why

    No ... there will be no visible discharge

    yes, but not a visible discharge

    The visible discharge, the spark, comes from the ionisation of the atoms of gas between the discharge points by the passage of the electrons across the gap
    if there is no gas to ionise, there will be no visible spark

  7. Mar 25, 2017 #6
    So it wouldn't be seen?

    Would it still generate heat?
  8. Mar 25, 2017 #7


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    Only in whatever target happened to be in the path of the electrons.
  9. Mar 26, 2017 #8
    Dense gas strongly obstructs passage of charged particles. If you apply sufficient electric field, the charged particles break an ionized path through the gas, either as spark or as arc - passing by the rest of insulating gas.

    If you pump a tube to a low pressure, at some point the current will spread out as a glow discharge.

    But on further evacuation of the vacuum tube, the glow in tube disappears, and instead the anode starts to glow. This is because now the electrons do not encounter (enough) gas molecules to obstruct them or to glow, but instead travel freely to anode.
  10. Mar 26, 2017 #9
    "Would current flow in a vacuum like space"
    Space is not technically a vacuum in the purest sense, it is almost entirely plasma teeming with freely moving charges such as electrons and ions. As such there are plenty of freely available charges to allow for the discharge. This type of discharge has been directly measured by THEMIS and Cluster;
    Although described as a "flux transfer event", it is an electric current (Birkeland Current) connecting the Sun to the Earth.
    These types of events have also been detected within Earth's magnetosphere/ionosphere as well;
    In plasmas there are three types of discharge phenomena, dark mode, glow mode, and arc mode. Here is a brief explanation written by a Professor of Electrical Engineering;
    To achieve a visible arc discharge, such as lightning, in the rarified density of space the current density would need to be increased exponentially.
    To summarize, yes currents can and do occur in space.
  11. Mar 26, 2017 #10


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    I answered the "title" question: "Would current flow in a vacuum like space?"

    As for the "body" questions, asked and implied:

    1. Would lightning work in space?
    2. Is "space lightning" invisible? ("I think it would but you wouldn't be able to see it?")
    3. What kind of device can separate charge in outer space? ("Let's say I have some sort of device that creates a lightning bolt")
    4. if I shot [space lightning] at a watermelon in a vacuum or another target [hoping a lemon will do] would it hit the target, or nothing happen because of the vacuum???​

    My stereotypically succinct answers are:

    1. There is no "lightning" in space. [1]
    2. See answer #1
    3. Multiple answers: Van de Graaff generator, Wimshurst machine, rubbing a balloon on your head(if you still have hair).
    4. Perhaps we should move this to the Sci-Fi forum.......​

    [1] Definition of lightning
    the flashing of light produced by a discharge of atmospheric electricity​
  12. Mar 26, 2017 #11
    There exist a natural phenomena that separates charges in space plasmas, it's called the electric double layer. These have been measured in situ by THEMIS and the Van Allen probes;
    These physical plasma layers separate charges and are precusors to electric discharges (currents) in space plasmas.
    Can these discharges be seen in space? Only if the current density is high enough to allow for glow or arc mode discharges.

    The idea this belongs in the sci-fi section just goes to highlight the misunderstanding of space plasmas in general and how misleading folks preconceived notions can be.
  13. Mar 26, 2017 #12


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    I believe I was referring to the

    I'm quite aware that "plasma" exists in space, thank you very much.
  14. Mar 26, 2017 #13


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    If one does a search on "vacuum breakdown", one will obtain A LOT of sources and published papers.

    Those of us who work with high-gradient structures can only WISH that (i) there are no breakdown problems and (ii) that we don't detect such a thing when it happens (which means that it doesn't matter!). Both of these are wishful thinking, meaning that such breakdowns do occur in vacuum, and that they can be detected, either from the disruption in the power/fields in the vacuum structure, and from visual evidence of light emission.

    The mechanism of vacuum breakdown can be involved and complex. The fact that you have a high gradient means that this is not just an empty space. There has to be at least one surface or source that is at very high potential difference when compared to something else. Otherwise, there will be no field.

    Most theories on such a breakdown starts with the emission of field electrons due to the high gradient. These are electrons that tunneled though the material, especially in regions where there are sharp, pointy topography (these are called high field-enhancement regions). At some point, if the field is sufficiently high, these field electron currents actually can heat up the emission sites. Heat implies outgassing of material. So this vacuum that you had before is not as good anymore, because the outgassing introduces species of atoms and molecules into the vacuum, especially around the heating sites. If the field-emitted electrons are energetic enough (after all, it gains energy after it leaves the material due to the external field), it can then ionize the outgassed atoms. And then a series of events can take place, including that the ionized atom (which has the opposite charge than the electrons), will be pushed back into the surface and cause even more stuff to be ejected.

    One can already see that in this complex sequence of events, a "casade" of charging-discharging of gas specie can happen, and the excited gas can emit light. This can often lead to the so-called vacuum breakdown. In an accelerator high gradient structure, it absorbs power, ruin the field geometry, and in some cases, leads to catastrophic failure of the structure itself.

    So yes, breakdown can happen in vacuum, and yes, they can be seen with the naked eye.


  15. Mar 26, 2017 #14
    Whether it be a watermelon or a Cassini, electric discharge occurs in space.
    Primary source;
    Lest we not get caught up on mere lightning alone as there are many types of electric discharges and frankly they are analogous to each other as the general physical mechanisms are similar. Whether it is visible to the narrow window afforded by humans limited ability to "see" the EM spectrum is sort of irrelevant, is it not? If a tree falls in the woods... If we can't see the discharge, does it still happen? Indeed it can.
    BTW, it would likely be more accurate to say space is plasma.
    Last edited: Mar 26, 2017
  16. Mar 26, 2017 #15
    This is going to sound really stupid I am sure... again I'm not physics major or anything along that nature so forgive my ignorance....

    Are there other currents that are immediately dangerous to be around?
  17. Mar 27, 2017 #16


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    Yes, but it involves taking a bath.

    Electrocution by iPhone charger (involving a bathtub)

    ps. There are a myriad of other electrical current events that can be dangerous to be around. Too many to mention, really.
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