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What can be detected in chunk of vacuum?

  1. Sep 29, 2009 #1
    Imagine a lets say sphere the size of an atom or so, somewhere in deep space, without any matter in it, just a mathematical volume of 3d space. Or a 1000x bigger if it would make a difference, for that matter.

    What can one expect to find or detect passing through it, in it in some period of time, lets say, one day?

    Even in single moment one should be able to collect complete picture of universe as we see it, right? With some time, all 'visible' stars, to great details and zooms? Almost all images from Hubble, complete and detailed maps of earth, sun and moon? Side note: Is there a limit to information we can get about visible universe, so that not matter how advanced optic apparatus we put inside our sphere we could only get that much information that entered our sphere? I presume there is a finite number of photons that passes through.

    What about other EM radiation in higher frequencies? What about other stuff? Gamma rays? Neutrinos? Gravity waves? Or some other particles or waves? And in longer time? Let's even suppose we know them all, I would guess list would not be short, or?

    Seems to me that in every tiny tiny part of 'nothingness' there is whole bunch of stuff going in all bunch of directions, most of it going around speed of light either. Now, do we know to reasonable extent that none of things going on in that chunk of space would interfere in one way or the other with 'matter' by changing it's momentum or any gravitational laws? If matter creates gravity which can affect light, why light, which really is everywhere, is not supposed to affect matter by same means, as a reaction force?
  2. jcsd
  3. Sep 29, 2009 #2
    We can't see stuff that's behind other stuff for one... And you have to get information about something (visually anyway) one photon at a time so that could be a problem at extreme distances (the distances you are talking about). Not to mention light only travels so fast so we are seeing things 'in the past' and they get more 'in the past' as they are further away from us. But we can get a pretty good idea with even these limitations. But not a truly complete one by any stretch.

    We look at that too, but mostly EM radiation in lower frequencies is what we care about because of doppler shifting of the light.


    We can look at gamma rays, we cannot know much about neutrinos since they pretty much don't ever interact with matter (there are billions passing through your body every second or something) except with their mega weak gravity. As for gravity waves, they are also super hard to detect if they even exist.


    There is more to know, every particle we know about and particles we don't know about are probably zinging around somewhere in space. Hardly a vacuum most of the time being filled with gas and radiation and whatnot.

    Well, I would not consider space filled with radiation a vacuum. And probably in a vacuum you would also assume there to be no gravitational influence (not actually possible in our universe but it's a simplification). Space is far from nothing, your right, it's (sparsely) filled with radiation and gasses.

    A 'chunk' of space can only influence another 'chunk' of space at the speed of light unless it is though a wave-function collapse, that's when the gloves come off. If there is matter there it will have gravity, electric charge etc. But yes, if it's void of matter it will have no gravity or charge, it will not influence other chunks much at all.

    Mass creates gravity, matter has mass. Because light does not have mass it does not create gravitational waves. Light is effected because it travels through what are called geodesics which is a fancy word that means that light takes the shortest path through a curved space-time (the curvature being gravity itself).
    Last edited: Sep 29, 2009
  4. Sep 30, 2009 #3
    First, thanks for you answers. I was kinda aiming at the quantity of different radiation and information that actually goes through every bit of space at any moment. Is it reasonable to say that just by "capturing" all events in realy really small piece of space and in small timeframe one can get enourmuos ammount of information about all universe? By capturing I mean in a sence of just writing down to paper all directions and frequincies of all type of waves that were in that spot in that time. Information being positions, sizes, spectral data, shifts and what not of vast number of space objects. And that goes for any bit of open space and for any given moment. That seems a lot to me.

    Just as a single hubble photo can caputre magnificent images, it is still very much reduced summary of all information that would pass in focal point of its lens. First off, you dont get to capture 360° sphere of an image just a small tiny projection of it's surface, and second you use filters to make it more meaningfull when just looking it with human eyes. And that is just EM radiation. So I'm just making a point: there is a vast sea of stuff literally everywhere, going in every direction, always.

    Now I want to talk about matter with mass, interactions, and kinetic energy of the mass. We can leave gravity aside for the time being. Do we know for sure, or to a reasonable belieif, that nothing from all that stuff can not interfere with kinetic energy of a matter floating out there at all? There is a lot of other interactions going on, heating (which is also kinetic but internal I understand), polarisation, and I don't know really what not. Isn't it reasanable to presume that something should be able to alter the kinetic energy of matter? Or more likely at least just apply the physical force, since there is probably same thing going on on the counter part of the object. Am I talking about radiatio pressure here?
  5. Sep 30, 2009 #4
    You can get a pretty good amount of information... But not a super amount. Your 'resolution' would be quite low as well as few photons would hit a small area in a small time compared to a larger area and larger times. There are other problems when you measure other things like gravitational waves, since you can have no net gravitational effect in one area but that can be simply because of destructive interference etc. So that can't be reliable in a small area either (or small time). Other issues come up as well, some of which I already mentioned.

    Right. But to what extent you can resolve information from that in a small area in a small time is not extreme as you might imagine, and that's with an impossible 100% efficiency capturing device.

    I don't fully understand but if your asking if light exerts pressure, it does, a little. Also sometimes neutrinos hit ordinary matter, but that's pretty rare... So if you have an object in deep space these things will happen, it will be pushed/pulled by light and neutrinos and other things will happen. It's just that these effects (and other similar effects) are pretty darn small.
  6. Oct 1, 2009 #5
    I guess you are right about amount of photons really comming through, it is big but not that big. Just found out that recent images from Hubble were "capturing" in literally days of exposure, "Almost single photon at the time".

    And you would be right about kinetic energy effect being small too. We could discuss the total impact on Sun or even Earth, but as proven, in no way it could be exerted on small objects (e.g. baseballs) in magnitutes of let's say gravity.

    Is there any info/calculations on ammount of it anyway? How does it compare to gravity, really? Thanks again.
  7. Oct 1, 2009 #6
    The pressure of light on earth is retardedly small, like in micro-pascals. But there is one place that the pressure is significant, the interiors of stars. In some stars even it can be the strongest force pushing from the inside (stronger than gas pressures etc.).

    Gravity is not directly comparable to radiation pressure... But in every natural circumstance I can think of it's much less strong.
  8. Oct 1, 2009 #7
    Thanks James. Do you in "pressure of light" include all EM radiation beside visible and all other fast traveling particles? And is that amount empirical or calculated?

    Interiors of stars would have high pressures, but from gravity in the first place, correct?
  9. Oct 1, 2009 #8
    Just the light (of every frequency) from the sun, not other particles. Also, it's calculated... but to a good margin of error... Different parts of the earth absorb more light than others etc.

    The a star, gravity in an inward pressure and light in this case would cause an outward pressure to counteract the gravity pulling inward.
  10. Oct 1, 2009 #9
    I am more interested in EMs (and effects of it) that comes outside solar system (perhaps maybe even get absorbed by sun). Are they accounted for?

    I'm not sure I follow you on star pressure thingie. You are saying there is "light" inside stars pushing matter outwards reducing total inside pressure created by gravity?
  11. Oct 1, 2009 #10
    What I told you was just the effect of the sun on the earth. The effect of electromagnetic radiations from deep space would be staggeringly small even by comparison.

    Yes, because the light in made inside the star and wriggles its way out. The effect is such that when a star runs out of fuel the amount of light bouncing around inside the gasses trying to find its way out decreases, so the outward pressure decreases and the star collapses under it's own gravitational field. This is a nova (AFAIK I'm bad at cosmology).
  12. Oct 3, 2009 #11
    Wow. I would imagine that is some pressure, holding the star from collapsing! Is it because of intensity (quantity) of light or it's high frequency (energy). Or both probably?
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