What is Invisible: Definition and 65 Discussions

Invisibility is the state of an object that cannot be seen. An object in this state is said to be invisible (literally, "not visible"). The phenomenon is studied by physics and perceptual psychology.
Since objects can be seen by light in the visible spectrum from a source reflecting off their surfaces and hitting the viewer's eye, the most natural form of invisibility (whether real or fictional) is an object that neither reflects nor absorbs light (that is, it allows light to pass through it). This is known as
transparency, and is seen in many naturally occurring materials (although no naturally occurring material is 100% transparent).
Invisibility perception depends on several optical and visual factors. For example, invisibility depends on the eyes of the observer and/or the instruments used. Thus an object can be classified as "invisible to" a person, animal, instrument, etc. In research on sensorial perception it has been shown that invisibility is perceived in cycles.Invisibility is often considered to be the supreme form of camouflage, as it does not reveal to the viewer any kind of vital signs, visual effects, or any frequencies of the electromagnetic spectrum detectable to the human eye, instead making use of radio, infrared or ultraviolet wavelengths.
In illusion optics, invisibility is a special case of illusion effects: the illusion of free space.
The term is often used in fantasy and science fiction, where objects cannot be seen by means of magic or hypothetical technology.

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  1. S

    Video demonstration of playing an invisible piano

    This is a demonstration on what he there calls a Graphene piano. I DO NOT BELIEVE THIS, in all honesty; unless someone here can instruct me differently:
  2. D

    Optical Where to look for a UV light that is invisible to the naked eye?

    Where to look for a UV light that is invisible to the naked eye? Essentially I want to buy a UV light that doesn't have that annoying blue glow, I just want the UV light that is invisible to the naked eye like infrared light. I read a bit about it and from what I read what I'm looking for is...
  3. Aidentheawesome23

    Invisible Ink that you can see through an IR lens

    I’m making an eyepiece that can see hidden messages, and I need to know an ink that you’ll be able to see through the IR lens.
  4. N

    Can the Invisible Man Reboot Exceed the Success of Kevin Bacon's Hollow Man?

    The reboot of Invisible Man will be shown next year: https://comicbook.com/horror/2019/08/22/invisible-man-reboot-remake-release-date-change-blumhouse/ Isn't this the same as Kevin Bacon Hollow Man? https://www.imdb.com/title/tt0164052/ I found Hollow Man so good. I wonder if it can even...
  5. Akshaya dhakal

    Can we see radio waves or other invisible waves with our eyes?

    There are many electromagnetic waves. Some of them are visible while other are invisible. Can we see those invisible electromagnetic waves? How Please give with scientific reason.
  6. Semiconductor

    B Unveiling the Mystery of Invisible Atoms

    If atom are invisible then how can one say that atoms are made up of electrons nucleus and quasi particles.
  7. AryaUnderfoot

    B The Invisible Beauty of Evening Primrose

    I understand that the wavelength of UV is too short to be absorbed by our cone cells, but I've came across 2 photos of evening primrose, which to our eyes are a dull yellow, but to insects (can see the UV light), it has a special pattern. My question is, I thought we're not able to see it. but...
  8. Mastico

    Special Ink invisible to the eye

    Greetings all, I am quite new to this forum so please forgive me if this is on the wrong thread. I recently purchased some reflective paint which sprays on clear and appears white/silver once light hits it at night. However I am looking for a type of paint that is invisible to the naked eye...
  9. N

    Could you make an opaque solid matter's electrons have the same....

    ... same energy levels of electrons as in glass. What would it take to change the eV levels of the electrons in the solid opaque matter, to the same energy levels of the electrons in glass. There is nothing necessarily special about glass, it is just a combination of silicon, sodium, and...
  10. N

    What is it about the EM waves that get absorbed by electrons

    What is it about the em waves that get absorbed by electrons compared to em waves that traverse solid material.What is it about that wavelength, or frequency of light, and other em waves that get absorbed by electrons, that makes visible light get absorbed by electrons. Why that specific...
  11. memoryerasure1

    How does light interact, and travel through Solid matter as

    How does light interact, and travel through Solid matter as matter gets thicker, in width.?In the absorbion, and emission process of light, hitting electrons, I do not really understand that much, about electron energy levels, and how they change when a lot of atoms become molecules, and them...
  12. memoryerasure1

    B Could mixing light wavelengths effect absorption, and emissi

    -ion process. The electron when hit by light moves to a higher shell level very briefly, to either shell 1, or 2 depending on the energy of the light wavelength. So because you mixed any EM radiation, with red light which has the lowest energy, could when light, or other EM waves gets absorbed...
  13. N

    B If you raise the electron to other higher shell states, can it affect light transmission?

    If you raise the electron to other higher shell states, can light transmission throug -h a SOLID BLACK opaque object. Modified the original question because it was unclear. I won't repeat the same question over, and over, but what I have said in previous questions may get repeated in the...
  14. N

    B Could the opacity of a material to one band of EM radiation be altered by X-ray illumination?

    -iation. Could the opacity of a material to one band of EM radiation (light) could be altered by irradiating the material with another band of EM radiation (X rays)? I think you are suggesting that: By raising the electrons in the atoms to higher energy bands (with the X rays), so that they will...
  15. N

    Does anybody know the energy shells eV for glass, and solid carbon?

    Carbon. So is it known what energy levels for electrons in glass atoms are in eV to move to a higher shell level. Glass does not absorb any light, except UV. but what is the eV for the glass electron to get excited and leave the ground state, and move up to shell level 2, or energy band 2. Also...
  16. N

    Whats the difference in glass electrons, and solid irons

    electrons in terms of absorption. To move from a lower to a higher energy level, an electron must gain energy. Oppositely, to move from a higher to a lower energy level, an electron must give up energy. In either case, the electron can only gain or release energy in discrete bundles. Now let's...
  17. M

    Why is clear glass see-through but not completely invisible?

    Why is a smooth clean piece of glass transparent but not invisible?
  18. P

    Which causes an object to become invisible, regular or diffused?

    When an object becomes invisible when it undergoes “regular” or “diffused” reflection?
  19. Justice Hunter

    Shrodinger's cat is "invisible"

    Thought-Experiment : Let's just say we have Schrodinger's cat setup, with the radiation apparatus in place we place our cat inside a fully transparent box, so that we could see the cat in it's superposition without opening the box, then we could see if it's alive and dead right? But this is...
  20. V

    Unveiling the Mystery of Invisible Spider Webs

    Hello everyone, I recently encountered that dreaded moment when walking where you get a face full of an seemingly invisible spider web. It got me thinking about why these webs are so difficult for humans to distinguish; unless of course we see them at the correct angle. Do they somehow bend...
  21. C

    How can we make invisible lights visible?

    Is there a way to combine lights that are not visible to our eyes and make them part of the visible spectrum?
  22. P

    Very small holographic laser projectors and diffraction.

    In thinking about what it would take to make a feasible invisibility cloak or holographic disguise or perfect hologram room, I've imagined something that works like this: A light beam "image" is projected onto a device designed to refract or reflect it in all directions, but only 1 color in any...
  23. T

    Is the Sun invisible at relativistic speeds? Part II

    ^^This is how the Sun would look from a distance of 4 light-years. If you add all the relativistic effects and stuff, wouldn't the Sun disappear from the visible spectrum? I was told that from a mathematical point of view, it is correct to say that some visible photons would still reach you, but...
  24. somasimple

    Invisible Charge: Solving for Equal Distance in Coulomb's Law

    "Invisible" charge? HI all,Homework Statement https://www.physicsforums.com/showthread.php?t=427862 See attached picture. q1 is at equal distance from A or B. k = coulomb's constant Homework Equations VA = (k q1 / r) VB = (k q1 / r)The Attempt at a Solution VAB = VA - VB = 0 V It seems...
  25. T

    Is the Sun invisible at relativistic speeds?

    At which speed does the Sun disappear from the visible part of the spectrum if I were to travel towards it at high speed? Let's assume there are no other stars in the visible universe and I'm a few light-years away.
  26. F

    OpenFTA radio buttons invisible in defining Primary Event

    I am test driving an app (OpenFTA, http://www.openfta.com) for small Fault Tree Analyses on Windows 7 64-bit. In one of the functions (defining a "Primary Event"), the radio buttons are not visible. Googling with the following search phrase does not yield anything relevant: open-fta...
  27. A

    Could dark matter be invisible bound states of ordinary matter or ehm, aliens?

    I've thought about dark matter and I'm wondering if it could possible be made up invisible bouond states of ordinary matter? Wikipedia says "According to consensus among cosmologists, dark matter is composed primarily of a new, not yet characterized, type of subatomic particle." But why a...
  28. S

    Why is Air Invisible? - Exploring the Possibilities

    Is it because the atoms constituting air are far apart? Or is it because they don't give out radiations in the visible range?
  29. K

    Would a massive collection of neutrons be invisible?

    Can accelerating neutrons emit electromagnetic waves? Will neutrons absorb or reflect EM waves? If not, what would a very large collection of neutrons look like? (I am assuming there are no protons/electrons present and the neutrons are not decaying)
  30. S

    Korea's upcoming invisible tower

    Not sure, but I think many would have known this: http://luxatic.com/invisible-tower-cheongna-city-tower-going-to-be-built-in-korea/ Would like to have comments since it is based on principles of optical physics (I'm not a physicist but just a curious Structural Engineer) if this is...
  31. A

    How can we see visible light since electric and magnetic fields are invisible?

    what do we mean exactly by visible light? Since light is oscillating electric and magnetic fields, and both electric and magnetic fields are invisible, what do we actually see? is color the wave itself?when we see colors do we see the waves themselves and if their wavelength were bigger would...
  32. B

    Using Optics To Make An Aircraft Invisible

    Using Optics To Make An Aircraft "Invisible" Homework Statement Does it seem possible (or practical) to make airplanes invisible to microwave radar by applying some kind of anti-reflection coating? Homework Equations The Attempt at a Solution I'm not sure what to say for this. I...
  33. S

    Invisible paint? is it possible?

    Hi is it possible(and exist for buying) invisible paint? such that with a camera and specific filter only i can see it? i need it for outdoor, draw on a road like for example and be able to see it with the camera from about 500 meters .. sry for my bad english.. thanks for help
  34. M

    Mirrors for UV Laser & Invisible Lasers

    Hi, Is there a such mirror which can reflects a UV laser (~190nm wavelength) with Reflectance greater than 95% and also invisible laser (not necessarily in a high Reflectance)? Thanks
  35. P

    Are electrically neutral particles invisible?

    As the thread title suggests, I was wondering if electrically neutral particles like neutrons can absorb/emit/reflect photons. I don't really have any sort of physics background so I'm not sure this question even makes much sense... but I vaguely remember hearing that photons don't necessarily...
  36. K

    Is It Possible: Invisible Wire

    Is it possible to make an invisible wire? Heres how It would work. You would have an electron gun shooting electrons and then you would have a wire carrying x amount of volts. Then you would put the wire into the electron flow. The electrons would then act as a wire and "transmit" the x...
  37. Char. Limit

    I'm on ur building, riding mah invisible bike

    O hai. http://laughingsquid.com/the-worlds-largest-lolcat-invisible-bike-mural/ I found this freaking hilarious, even if it is old. And for those of you who don't know what LOLcats are (shame on you!), here's a TVTropes explanation: http://tvtropes.org/pmwiki/pmwiki.php/Main/Lolcats...
  38. Loren Booda

    How many U.S. citizens are excluded from society due to disability?

    How many U.S. citizens are currently secured (institutionalized) from participating in free society, primarily because of incapacitating mental or physical disability?
  39. D

    How Does Glycerine Make a Bottle Invisible?

    http://www.youtube.com/watch?v=anJuZdL_vsw&feature=fvhl What is going on here?
  40. G

    China's Invisible Man: Wowing with Amazing Art

    Yeah he's pretty cool. Check out he gallery http://news.ninemsn.com.au/glance/840836/invisible-man-wows-with-amazing-art
  41. K

    Mass of invisible binary companion

    Hey guys, got this question that's been giving me some trouble. The spectral lines in a low-mass main sequence star are observed to show sinusoidal velocity variations with an amplitude of 500km/s and a period of ten hours. Calculate the lower mass limit of the unseen binary companion...
  42. S

    Why is visible light invisible?

    Please take a look at this link http://www.warpedspace.org/lightingT/Images/LightProperties/LightReflection.jpg My question is: why can we see the blue floor but not the incident and reflected rays of light?
  43. A

    Cancer Mutations: Visible or Invisible?

    And what type would that mutation be? Would it be correct to say that cancer mutations are not always visible, and one could run tests to see if the person has cancer?
  44. P

    Question -Substiution ALWAYS imagining invisible brackets in your head?

    Im in 2nd year of math now...so I know algebra but I was reading this from this website: "Substitution Every time we replace a part of an expression with a value or another expression, we are using the technique of Substitution. And, every time a substitution is performed, parentheses...
  45. X

    Exploring the Possibility of Invisible Matter Existing in Different Dimensions

    Invisible matter... since the universe is made up of mostly invisible matter, are they in different dimensions that's why we can't detect them? such as some say the deads live in the same world that the livings live, except in a different layer or dimension?
  46. rootX

    Invisible Color

    I finally managed to make my text invisible .. (I had to use it somewhere) :biggrin: Invisible text ... Select above COLOR="#E1E1E2"
  47. S

    Making an Invisible Fishing Hook: Attractive to Fishermen?

    I would like to know if it is possible to make a hook that would be transparent. I think this would be attractive to fishermen.
  48. J

    Metal invisible in the ultraviolet?

    I was reading the plasmon chapter of my solid state physics book and it says simple metals should reflect light in the visible region and transmit it in the ultraviolet, roughly speaking. (I think I read in a paper that for some metals, like Au and Cu, the threshold wavelength is in the visible...
  49. S

    The Possibility of Making Objects Invisible Using Sound and Light

    I herd that a group has discoverd a way to bend sound around an object. Now if we can do that there is was to do that with light, right. So that would make that object invisible. Is this theory correct.
  50. C

    Future Human: Making human's invisible without a suit

    Greetings, in the physics forum we've had a discussion on how to make a person invisible. Many people suggested complicated invisibility suits which I won't get into. I had an idea of how we could possibly biologically engineer a human body to be invisible without the need for a suit. I'm...
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