Is there such a thing as true darkness?

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The discussion revolves around the concept of true darkness and whether it exists in the universe, given that electromagnetic radiation permeates all space. It argues that since all objects emit thermal radiation, even in total darkness, there are always some photons present, suggesting true darkness may not exist. The conversation also touches on the definitions of light and darkness, emphasizing that human perception is limited to the visible spectrum, while other forms of electromagnetic radiation exist beyond it. The debate extends to the nature of photons, questioning their mass and whether they can be considered substance despite being massless. Ultimately, the consensus leans towards the idea that while true darkness may be a subjective experience, it likely does not exist objectively in the universe.
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Considering that what most people think of as light is just the visible spectrum of electromagnetism, while much more exists on either end, are the frequencies beyond either end of the visible spectrum still light? If so, since electromagnetic fluctuations permeate the known universe, is there any such thing as true darkness?
 
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If you consider the radiated thermal spectrum of an object at finite temperature the you could expect the occasional photon of visible em radiation even inside a coal mine with the lights all turned off. But, to an Engineer this is near enough darkness for Jazz!
 
Yes, if humans define darkness as the absence of photons in the visible spectrum that can be received by retinal cells.

Of course if you lock yourself in a room shut off from enough receivable energy in the visible spectrum your brain will eventually start making things up for you.
 
This is a very complex question to my thinking.
Do you mean subjective or objective darkness? If the former, I submit that a totally blind person might be considered to be in true darkness regardless of environment. Even that might depend upon the pathology. If a sighted person is in an enclosed room or simply sticks his head into a box, he'll "see" spark-like dots due to random interactions of cosmic rays or other irritating things with the photoreceptive cells in his eyes. They're called "phosphenes". That, to me, counts as vision, but can it be considered "darkness" simply because no photons are involved?
 
I wouldn't class 'seeing things' that aren't there as vision. It's more like 'imagination'.
 
sophiecentaur said:
I wouldn't class 'seeing things' that aren't there as vision. It's more like 'imagination'.
The whole point is that they are there. They're subatomic particles. Would you consider a track in a cloud chamber to be imaginary just because you can't see the particle that created it?
 
The whole EM spectrum is light, and the light that we see is visible light. There is such a concept as true darkness, but based on what we observe it's very likely that this true darkness doesn't exist anywhere in the known universe. Even if you put someone in deep space, inside a black box, the box material would still emit thermal radiation inward because its temperature is above zero.
 
MikeyW said:
The whole EM spectrum is light, and the light that we see is visible light. There is such a concept as true darkness, but based on what we observe it's very likely that this true darkness doesn't exist anywhere in the known universe. Even if you put someone in deep space, inside a black box, the box material would still emit thermal radiation inward because its temperature is above zero.

This is more to the point which i was after. The others were digressing into human biological interpretation of the visible spectrum as opposed to the full natural spectrum. This seems a relatively definitive argument in my favor.

With that being said, I'll pose a new question:

If there is no true darkness in the known universe due to electromagnetic fluctuations, are the resultant radiations from said fluctuations which fall outside either end of the visible spectrum still photons? or is the visible spectrum alone defined by the manifestation of photons?

I am just now getting into physics with more depth than before so I may be posing an ignorant question here, but it will help me know whether or not to ask the next question which I have in mind.
 
The photons can be in the visible range or outside of it. I would hazard a guess that most are in the microwave region (the cosmological background radiation), but there are still some in the visible region from non-blackbody sources, eg. starlight. I'm not sure whether a human eye could detect it in the darkest regions, but it's still there.
 
  • #10
MikeyW said:
The photons can be in the visible range or outside of it. but there are still some in the visible region from non-blackbody sources, eg. starlight.

Stars are black bodies. And everything is actually a black body. The name is misleading. As everything emits radiation. Cooler objects you can't see it, because the intensity of the light is very weak in the visible spectrum. But as they get hotter, the intensity of the light increases in the visible spectrum and you can see the light. First they glow red and then white hot (white hot as it's called - and if it is glowing white then it is hot).

There is always visible light everywhere - there's just not always enough to see it. Even deep space is full of starlight.

Here's a graph of black body radiation, and the visible spectrum. You see you need quite a bit of heat to see the heat.
http://www.egglescliffe.org.uk/physics/astronomy/blackbody/Image21b.gif
 
  • #11
Even if you shut yourself in a perfectly opaque box in deep space, the box will come in thermal equilibrium with the cosmic microwave background, rise to 3 kelvin, and reradiate that heat continously according to a (mostly) blackbody curve. Even at just 3K, there is some amount of radiant intensity at visible wavelengths.
 
  • #12
phaeton said:
This is more to the point which i was after. The others were digressing into human biological interpretation of the visible spectrum as opposed to the full natural spectrum. This seems a relatively definitive argument in my favor.

If you don't digress into how humans perceive the world about them through EM waves, chemical means, or pressure receptors with the question that was posed in this case, one can go way off into fantasy land. In fact at the base of any scientific activity one must always be cognisant of the limitations of human perception. People completely forget so many filtering mechanisms, etc... that the brain has given us through natural selection that don't have a darn thing to do with finding photons.

We merely got rid of that rubbish for you to get to the serious stuff :)

Thank god I can't always feel my clothes touching all parts of my body... it would be damn difficult for me to type in this particular discussion.
 
  • #13
All electromagnetic radiation propagates by way of photons.

'Light' is a tricky term; it tends to be human-centric. Bees and birds and many other animals can see well into the IR and UV range, using optical sensors, so that is one way of defining light that is not human-centric.

If you go much farther outside the visible spectrum, you can no longer use optical sensors. You get into microwaves on one end and X-rays on the other.
 
  • #14
pgardn said:
I can't always feel my clothes touching all parts of my body
Thanks a lot, you saboteur! Now I'm starting to itch.
 
  • #15
Danger said:
Thanks a lot, you saboteur! Now I'm starting to itch.

So now you can think about your breathing ;)
 
  • #16
pgardn said:
So now you can think about your breathing ;)
:smile:
(I don't know whether or not you actually realize how funny that is, given my circumstance.) :biggrin:
 
  • #17
krd said:
Stars are black bodies. And everything is actually a black body. The name is misleading. As everything emits radiation. Cooler objects you can't see it, because the intensity of the light is very weak in the visible spectrum. But as they get hotter, the intensity of the light increases in the visible spectrum and you can see the light. First they glow red and then white hot (white hot as it's called - and if it is glowing white then it is hot).
You got me on this one. "non-blackbody" was an awful word for me to use.
 
  • #18
Muphrid said:
Even if you shut yourself in a perfectly opaque box in deep space, the box will come in thermal equilibrium with the cosmic microwave background, rise to 3 kelvin, and reradiate that heat continously according to a (mostly) blackbody curve. Even at just 3K, there is some amount of radiant intensity at visible wavelengths.

DaveC426913 said:
All electromagnetic radiation propagates by way of photons.

'Light' is a tricky term; it tends to be human-centric. Bees and birds and many other animals can see well into the IR and UV range, using optical sensors, so that is one way of defining light that is not human-centric.

If you go much farther outside the visible spectrum, you can no longer use optical sensors. You get into microwaves on one end and X-rays on the other.

This is great. I had suspected this would be the case. Thank you all for helping me work through this. Now I must pose yet another question which will take me closer to my end goal:

Since, in a matter of speaking, there is "no true darkness," because there are photons being propagated within every vestige of the known universe, would that imply that the universe as a whole is made entirely from and full of substance?

To qualify, this touches on a still raging debate on whether photons actually have mass or not, or whether photons have both mass and no mass at the same time(in a similar way that photons act as both wave and particle). From the standpoint that photons do indeed have mass, and from the technical definition of substance as the mass or tangibility of a thing, then it would follow that the answer to my above question would be yes. But it could also be argued that as photons have no mass, and hence, no literal substance, and that literal substance is scarce in the universe. This would leave us with a no to my above question.

Now, touching on the metaphysical side, and re-qualifying what substance is outside of it's literal and physical definition, even if photons have no mass, could it be argued that they still have substance? Which would allow for a yes to my [first] above question in either case.

Now to pose my suggested re-qualifying of what substance is: can something which has function, lack substance? For photons, whether mass-less or not, have function. If something has function, would that not imply, philosophically, that it must have substance?

I fear though that I may be posing a question which cannot be properly answered in a general physics forum, so pardon my digression, against my own previous resistance, into human perceptions.
 
  • #19
phaeton said:
Since, in a matter of speaking, there is "no true darkness," because there are photons being propagated within every vestige of the known universe, would that imply that the universe as a whole is made entirely from and full of substance?

No, it would not.
 
  • #20
jbriggs444 said:
No, it would not.

And your reasoning is...?
 
  • #21
phaeton said:
I fear though that I may be posing a question which cannot be properly answered in a general physics forum, so pardon my digression, against my own previous resistance, into human perceptions.

With any discussion as difficult as this one can always digress into human perceptions. Definitions become extremely important. Many times you will discover that people do not even have the same definition of some noun (and the don't realize it) and this leads to disagreement. Their models, since this is all modeling, don't fit with each other because they do not even agree on the same basic definitions. They may even have the same mathematical definition but then the metaphorical model in their heads actually differ.

It usually happens because most of us are humans and realize limitations in symbolic language and reasoning.

There are groups of physicists and philosophers that are trained in both that look for flaws in some very important topics in physics. And there are many papers and groups that do exactly what you are attempting here.
 
  • #22
phaeton said:
To qualify, this touches on a still raging debate on whether photons actually have mass or not, or whether photons have both mass and no mass at the same time(in a similar way that photons act as both wave and particle). From the standpoint that photons do indeed have mass, and from the technical definition of substance as the mass or tangibility of a thing, then it would follow that the answer to my above question would be yes.

Is there a "raging debate"? Experiments to find the rest mass of a photon have all come up with steadily decreasing values for the maximum possible mass but, of course, will never yield a value of Zero because that's how measurement works; you cannot measure Zero.
 
  • #23
pgardn said:
There are groups of physicists and philosophers that are trained in both that look for flaws in some very important topics in physics. And there are many papers and groups that do exactly what you are attempting here.

It certainly does become more tricky when trying to reconcile two seemingly divergent schools of thought. Though, it is lately becoming more accepted that interdisciplinary approaches are far more beneficial. Do you by chance have an opinion on this particular matter?
 
  • #24
sophiecentaur said:
Is there a "raging debate"?

I was merely referencing my introduction to this forum. I was looking for some answers to said debate when I was lead to a thread on this forum which is in it's sixth year on continually renewed interest and debate. I may have chosen poorly when using the word "raging" but it seemed to me that there are still are large number of people on both sides of this issue. It may also be my own ignorance which I can blame, but it seemed to me that the arguments were nearly in favor of photons having mass/substance in some way or another.

My mind is a blank tablet, I'm here to learn.
 
  • #25
phaeton said:
I was merely referencing my introduction to this forum. I was looking for some answers to said debate when I was lead to a thread on this forum which is in it's sixth year on continually renewed interest and debate. I may have chosen poorly when using the word "raging" but it seemed to me that there are still are large number of people on both sides of this issue. It may also be my own ignorance which I can blame, but it seemed to me that the arguments were nearly in favor of photons having mass/substance in some way or another.

My mind is a blank tablet, I'm here to learn.

Photons have energy, which contributes to gravitation. They can impart momentum to objects and once absorbed the energy adds to the mass of a system. In fact, any system with light in it is more massive than a near-identical system that has no light. So we say light has no REST MASS, but it does indeed have energy and thus can add mass to a system, though it has no mass itself.
 
  • #26
Drakkith said:
Photons have energy, which contributes to gravitation. They can impart momentum to objects and once absorbed the energy adds to the mass of a system. In fact, any system with light in it is more massive than a near-identical system that has no light. So we say light has no REST MASS, but it does indeed have energy and thus can add mass to a system, though it has no mass itself.

Excellent, that seems relatively straight forward... But seeing as how photons are capable of such things, capable of anything at all, would that not lend credence to thought of photons possessing substance, whether that be mass or energy? Maybe a better question is whether or not substance should be re-defined as encompassing more than mass, but energy as well...
 
  • #27
phaeton said:
Maybe a better question is whether or not substance should be re-defined as encompassing more than mass, but energy as well...
An even better question: is there a scientifically rigorous definition of the word 'substance' in the first place?
 
  • #28
phaeton said:
And your reasoning is...?

To say that the universe has electromagnetic radiation throughout and conclude that it is both full of and made from some unspecified substance... That is not a coherent argument. And the conclusion is not testable.
 
  • #29
DaveC426913 said:
An even better question: is there a scientifically rigorous definition of the word 'substance' in the first place?

Oh Dave!
You know ---- stuff, gubbins, guff or something.
:devil:
 
  • #30
DaveC426913 said:
An even better question: is there a scientifically rigorous definition of the word 'substance' in the first place?

substance [ˈsʌbstəns]
n
1. the tangible matter of which a thing consists
2. a specific type of matter, esp a homogeneous material with a definite composition
3. the essence, meaning, etc., of a written or spoken thought
4. solid or meaningful quality
5. (Physics / General Physics) material density a vacuum has no substance
6. material possessions or wealth a man of substance
7. (Philosophy) Philosophy
a. the supposed immaterial substratum that can receive modifications and in which attributes and accidents inhere
b. a thing considered as a continuing whole that survives the changeability of its properties
8. (Christian Churches, other) Christian Science that which is eternal
9. a euphemistic term for any illegal drug
in substance with regard to the salient points

Here is what i found to be a collection of modern definitions of the word substance, I made bold the definitions which i thought to be pertinent. The first and fifth the the ones which i seem to be having trouble with. It is this definition which I seem to want to change in a way which includes energy as well. If this were the case then the fifth definition would be nullified. I believe this is a proposition worth looking into and capable of supporting. The forth definition suggests that things with meaningful qualities posses substance, and I believe photons to fall within this category.
 
  • #31
phaeton said:
substance [ˈsʌbstəns]
n
1. the tangible matter of which a thing consists
2. a specific type of matter, esp a homogeneous material with a definite composition
3. the essence, meaning, etc., of a written or spoken thought
4. solid or meaningful quality
5. (Physics / General Physics) material density a vacuum has no substance
6. material possessions or wealth a man of substance
7. (Philosophy) Philosophy
a. the supposed immaterial substratum that can receive modifications and in which attributes and accidents inhere
b. a thing considered as a continuing whole that survives the changeability of its properties
8. (Christian Churches, other) Christian Science that which is eternal
9. a euphemistic term for any illegal drug
in substance with regard to the salient points

Here is what i found to be a collection of modern definitions of the word substance, I made bold the definitions which i thought to be pertinent. The first and fifth the the ones which i seem to be having trouble with. It is this definition which I seem to want to change in a way which includes energy as well. If this were the case then the fifth definition would be nullified. I believe this is a proposition worth looking into and capable of supporting. The forth definition suggests that things with meaningful qualities posses substance, and I believe photons to fall within this category.

Why? Since it doesn't fit the other definitions - eg. energy is not tangible and is not matter - why redefine a word that means one thing to mean something else? Why not redefine matter to include energy? Or solid to include vacuum? Or 'one' to include all numbers up to ten?
 
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  • #32
jbriggs444 said:
To say that the universe has electromagnetic radiation throughout and conclude that it is both full of and made from some unspecified substance... That is not a coherent argument. And the conclusion is not testable.

Substance is unspecified by nature. I am proposing that substance include energy as well as mass, in which case my original question would appear to have a positive answer as opposed to negative. Attempts at the specification of energy's signatures across the universe would be the result of entirely different types of questions and research, not to mention nearly impossible.
 
  • #33
The fact that there are so many versions of the definition of 'substance' implies that it the meaning is not universally accepted. That makes it a poor quantity to use, without explicitly defining it first (each time).

But I don't see where the terms has to be used, in any case, when the existing terms seem to serve very well.
 
  • #34
sophiecentaur said:
The fact that there are so many versions of the definition of 'substance' implies that it the meaning is not universally accepted. That makes it a poor quantity to use, without explicitly defining it first (each time).
Not to mention the fact that it has yet to be quantified if it is going to be used in physics.

We can't use kg, as that is a matter unit. We can't use Joules as that is an energy unit. I propose we use the unit gubbin.

"This volume of space contains several planets - at least a Gigagubbin. But it is also strongly irradiated by its sun, comprising another 2 Gigagubbins of substance."
 
  • #35
Muphrid said:
Even if you shut yourself in a perfectly opaque box in deep space, the box will come in thermal equilibrium with the cosmic microwave background, rise to 3 kelvin, and reradiate that heat continously according to a (mostly) blackbody curve. Even at just 3K, there is some amount of radiant intensity at visible wavelengths.
My two cents: the amount of radiant intensity at visible wavelengths from a 3 K black body is so low that the resulting photons would be discrete events. So there would be periods between them where the interior of the box is perfectly dark.
 
  • #36
Or Dollop!
 
  • #37
DaleSpam said:
My two cents: the amount of radiant intensity at visible wavelengths from a 3 K black body is so low that the resulting photons would be discrete events. So there would be periods between them where the interior of the box is perfectly dark.

Where would you draw the line? All photons are 'discrete events'
It's a bit like sound radio in which all hell breaks loose at the transmitter if there's more than about one second's worth of silence 'cos they think they've lost their programme feed.
 
  • #38
DaveC426913 said:
Why? Since it doesn't fit the other definitions - eg. energy is not tangible and is not matter - why redefine a word that means one thing to mean something else? Why not redefine matter to include energy? Or solid to include vacuum? Or 'one' to include all numbers up to ten?

Is energy truly not tangible? We perceive tangibly the effects of energy all around us. Light is both wave and particle, so what if substance actually is somehow both matter and energy in a similar way?

Consider this picture for a moment:
921.jpg


This is how I imagine light to be both wave and particle. If you look in the center you see a vase with only background on either side, but if you refocus your eyes on the background the two faces become the focus and what's in between, what was a vase, is now just background instead. Both vase and faces define each other, without one or the other the forms become meaningless. In the same way I believe waves and particles to be defining each other and making up the whole that is light. This discussion has lead me to believe there may even be a similar connection between matter and energy. This would mean that both are intrinsic in each others very being, lending credence to the possibility that both posses substance.
 
  • #39
This wave - particle duality thing has really been done to death. Photons are Photons and Protons are Protons. Why should they have to fall into one category or another? People just have to get over it, I'm afraid. Just listen to what Feynman had to say about it. I think, in his grumpy way, he got it just right.
 
  • #40
DaveC426913 said:
Not to mention the fact that it has yet to be quantified if it is going to be used in physics.

We can't use kg, as that is a matter unit. We can't use Joules as that is an energy unit. I propose we use the unit gubbin.

"This volume of space contains several planets - at least a Gigagubbin. But it is also strongly irradiated by its sun, comprising another 2 Gigagubbins of substance."

lol, we'll need to petition for this indeed :D hehe
You do make a very good point though...
 
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  • #41
I don't see the issue here. Light has energy. Energy gravitates and contributes to the mass of a system. What possible reason would we have for trying to come up with something new and calling it "substance"?
 
  • #42
sophiecentaur said:
Where would you draw the line?
It is easy to detect a single photon with a photomultiplier tube. I would draw the line there. If a PMT cannot detect light then I would say it is perfectly dark at that time.
 
  • #43
Now you see it - now you don't?
A bit like the direction indicators on my car. Half the time they're not working!

Why are we trying to define what we mean by 'zero' in any case? It's a bummer. You can never prove that something doesn't exist. You can only say that you didn't spot it when and where you were looking.
 
  • #44
sophiecentaur said:
Now you see it - now you don't?
A bit like the direction indicators on my car. Half the time they're not working!
Or half the time when they are working they are dark.
 
  • #45
phaeton said:
In the same way I believe waves and particles to be defining each other and making up the whole that is light. This discussion has lead me to believe there may even be a similar connection between matter and energy. This would mean that both are intrinsic in each others very being, lending credence to the possibility that both posses substance.
The connection between mass (in case you intended this with "matter") and energy is very simple: a system's mass is its energy (divided c2) in a frame of reference where the system is stationary. A photon has no mass, but a photon in a stationary box gives mass to it. The same for the photons in the universe: they give mass to it. Someone made the computation of the total mass given to the universe by CMBR's photons, but it doesn't approach dark matter's mass (for example).
 
  • #46
phaeton said:
Considering that what most people think of as light is just the visible spectrum of electromagnetism, while much more exists on either end, are the frequencies beyond either end of the visible spectrum still light? If so, since electromagnetic fluctuations permeate the known universe, is there any such thing as true darkness?

Not true darkness but close to the darkness that you are inquiring about. There is a cold spot in the CMB map that ESA's Planck satellite had plotted, I assume there is very few em waves there. WMAP satellite detected it too, and VLA radio telescope looked at it too and saw fewer galaxies. Boomerang nebula is the coldest in the observable universe but I saw a lot of em waves there hence it's unlike the CMB cold spot.

Btw, the CMB cold spot is located in the constellation Eridanus, a string of stars which start at the vicinity of the Orion's Rigel. And the Orion is rising after midnight this time of the year, interested to see darkness through a telescope? Maybe not :D
 
  • #47
phaeton said:
Considering that what most people think of as light is just the visible spectrum of electromagnetism, while much more exists on either end, are the frequencies beyond either end of the visible spectrum still light? If so, since electromagnetic fluctuations permeate the known universe, is there any such thing as true darkness?
A black hole is rather dark. But the collapsing matter around it might obscure the view on its absolute darkness.
 
  • #48
A.T. said:
A black hole is rather dark. But the collapsing matter around it might obscure the view on its absolute darkness.

No, that is not true at all. Matter spiraling into a black hole radiates. The black hole itself emits Hawking's radiation.
 
  • #49
Photons have only been free to roam the universe since the time of recombination. Prior to that they were trapped in a dense plasma that permeated the entire universe.
 
  • #50
Using what everyone has posted it could be that photons are a substance, since everything is composed of energy. But seeing that most people would try to argue that "specific type" of energy is what matters. I leave it as a case solved for now till we have more information regarding "energy".
 
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