Light mostly doesn't scatter in a vacuum, but it does a little teeny bit because of the photons interacting with each other as they travel almost parallel but not the same wavelength and polarity (that would be laser light).

In the solar system, it's pretty negligible. If you get outside the atmosphere, the size of your lens/reflector and the brightness for far-out objects are the only limits to human-scale resolution. I don't know the math off the top of my head, but I doubt self-interference in the light would cause problems with even milimeter-on-Pluto-from-Earth resolution if you had a big enough telescope to capture and magnify that image.

Can anyone with more optics/physics/astronomy than me confirm, deny, or elaborate on that?

There's a lot of nothing in space, so not much scattering happens until the light reaches the Earth's atmosphere. The images we get from such telescopes as JWST are "diffraction limited", which means that the resolution is a function of the size of the telescope's mirror, in the case of JWST it's the mirror segments that cause the starburst pattern. A huge single-mirror telescope in space could make much higher resolution images.

It is also limited by the wavelength of the light that is collected. For most of the IR range the JWST actually has slightly lower resolution than the Hubble since while its mirror is several times bigger the visible light Hubble collected has a shorter wavelength than the IR of JWST and that more than makes up for the difference.

The smallest size that can be resolved by an optical system is given by the size of the Airy disc. This is aa property of the system, and is one measure of the quality of the system. Mirror systems will have smaller Airy discs than lens systems because they have no chromatic aberration, and large diameter optics generally have smaller Airy discs than small optics, for example.

Oh, hey, the Airy Disk! I remember that from an undergrad physics class. Wikipedia reminds me that I'd know that ~1.22 factor for 'infinite' focus anywhere...

That’s usually not a limiting factor since you would lose the resolution of features smaller than IR wavelength so unless you are trying to resolve ants on Jupiter it won’t matter too much for astronomers!

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That's not the same principle. The diffraction limit pertains to angular size, not physical size. You are correct that you wouldn't be able to resolve things smaller than a given wavelength, but the diffraction limit can apply to arbitrarily large objects as long as they appear small. A 100,000-light-year-across galaxy will simply appear lower resolution in an IR telescope than a visible-light telescope of the same aperture/focal length.

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What is the theoretical limit, if we had any size perfect mirror?

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While I agree most of the scatting is happening in our atmosphere, and that space is mostly nothing, it’s not completely nothing and when there is something there tends to be a massive amount of something there. There is a lot of dust, and there is a lot of space between us any any of there light source there is out there. And anything that we are interested is where a bunch of stuff is. This is why we want to look at the IR spectrum instead of the UV spectrum because IR light scatters much less in the presence of dust, and the UV spectrum of light can be scattered or blocked a lot easier.

Yes, the interstellar medium (ISM) is rather opaque to visible light, but more transparent to infrared. My day job is in millimeter wave radio astronomy, which studies the makeup and behavior of the ISM.

There's not much of a theoretical limit to the resolution. If you can make a telescope the size of the galaxy, it would have quite high resolution. But where would you put it?

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"Put" is not the problem so much as collecting the data in one place. EHT, for instance, is a telescope the size of planet Earth. The practical limit on its ability to inform our awareness of the universe is assembling what it can see.

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If I recall correctly, this is why most of what we've seen beyond our galaxy is to galactic "north" or "south". If we aim our telescopes along the galactic plane, there's a ton of dust in the way (the "milky way" you can see with your eyes when in a dark enough location) that makes it hard to see anything past that.

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Exactly. The diffraction limit has to do with the limiting spatial frequency of the system, so for telescopes it's usually their apertures.

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Does the inverse square law cause scattering?

The thin gas in the galaxy - what we call the "interstellar medium" - does scatter and disperse photons. This effect is small at high frequencies (like visible light), but increases as you go down to lower frequencies (radio waves etc). But even in radio waves, we're still limited more by the resolution of our telescopes than the fuzziness causes by the galaxy's "atmosphere" - although the Event Horizon Telescope is awfully close to the point where that matters.

What we do see is that radio waves of different frequencies take a different time to reach us, and will be a little out of phase. So if some event happens that emits radio waves are a broad range of frequencies, we don't get receive that emission at once. Instead, the higher frequency radio waves arrive first, and the low frequency waves arrive later. Instead of a single broad pulse, what we get is like a quick glissando from high pitch to low pitch.

You can actually use this to measure the thickness of the interstellar medium. The slower the slide in pitch is, the more material was along the path of the radio wave. So if you already know the source and the distance to the source, you now know the "column density" of interstellar stuff between Earth and the source. Do that with a bunch of sources and you start to build a map of the density of stuff in the galaxy, which can be used to complement other measures for the interstellar medium.

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> because of the photons interacting with each other as they travel almost parallel but not the same wavelength and pola

Isn’t the electromagnetic force linear up until very high energies? What do you mean interact?

What about dark matter? Can it block light or distort it?

I believe that limitation is for visible spectrum telescopes. IR telescopes can see through the dust because IR is not impacted as much.

One source: https://www.esa.int/Science_Exploration/Space_Science/Herschel/More_about_the_infrared

Thank You for the information ☑️🌚

There is a concept where we could use the sun’s gravity to make an effectively huuugggeee telescope, enough to image exoplanets. https://en.m.wikipedia.org/wiki/Solar_gravitational_lens

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Whatever dark matter is, if it truly exists, appears to not interact with the electromagnetic field at all. This means that to light, dark matter doesn’t exist. So it would cause no change to any light passing through it. Dark matter does interact gravitationally so with enough of it one one place it can change the path of light causing a gravitationally lensing effect.

Fun fact, since it doesn’t interact with the EM field dark matter also can’t clump like normal matter does because you need those charge interactions to dissipate energy to slow down enough to clump. So dark matter just sort of oscillates back and forth through the center of gravity like a pendulum. This is why it always looks the same regardless of galaxy and why it’s always bigger than the galaxy.

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Others have mentioned that light doesn't scatter in a vacuum.

However, light gets dimmer with distance. according to an "inverse square law". This has at least two implications.

• Astronomers must use wider telescopes and leave the camera open over a longer time to capture enough light to see stuff far away.

• Astronomers can use increasing dimness at greater distances to measure distance. In 1924, Edwin Hubble used the increasing dimness of Cepheid variable stars in the Andromeda Galaxy to claim the Andromeda nebula was actually another galaxy outside the Milky Way Galaxy. Source

People are focusing a lot on the word "scatter", while I think you might just mean that the photons separate enough, due to a tiny difference in angle, that the huge distance would make it low-resolution. And yes, that does indeed happen, which is why bigger telescopes = more resolution, because it can capture more of the spread-out photons

Actually if you take a few light years at light speed without something to deflect or absorb energy from free floating hydrogen and dust your ship would be destroyed before you even reach the closest star outside our solar system. and they constantly say light from anything far away goes through alot of gases and stuff which is why they can see some of it in the first place.

Also at least 1 ok art of f hydrogen or dust poo er square meter. That's alot of stuff over several light years.

The bigger issue is the lack of far away galaxies missing a feature that is required if space is expanding. Should have Magnified images further away at the distances viewed so far.... But if it does then either the galaxies viewed are far brighter than galaxies closer and far smaller not fitting the standard model.

If images are right space time isn't expanding and that whole matter can't go faster than light becomes an issue as galaxies are still measured to be moving away at Lightspeed or faster. Not looking good for the big bang either since they found far more galaxies than expected at an age of the universe where the model doesn't fit....

Everything from gravitational lensing to warp drives might need all new equations now... They don't want to say that tho or they would have by now....

Only way to account for red shift would be if the light is smeared as it's emitted.

Or lengthen on it's own the further it travels meaning light speed isn't constant and equations have to be recalculated to find the true age of things as they appear... Easier one would be if the light is emitted and drops to light speed as it is and the object emitting the light is moving relative to some other non expanding field the light latches onto. But then there should also be such high energy on the far side of the galaxies moving away at light speed+ that it should be measurable if it's there and if our technology can even see it with how it would technically be a wave that overtakes itself cause of the objects movement. So it should blue shift and then red shift at some speed as galaxies accelerate more somehow... They still haven't even bothered to address that matter at Lightspeed without expanding space issue yet either....

Thank you!

Nope, scattering is a change in the direction of light due to an interaction. The inverse square law is just a geometric spreading of the light from a point source in the absence of an interaction.

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