Questions tagged [photons]

Questions regarding a type of elementary particle with 0 mass and is a quantum of the electromagnetic field. Photons always travel at constant speed in a vacuum.

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What is the density of photon energy in intergalactic space? [duplicate]

What is the average density of photon energy (over all wavelengths) in intergalactic space? In other words, if you took a typical cubic meter of intergalactic space, how much electromagnetic radiation ...
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3 votes
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How would white light cavities (WLC) work for gravitational wave detection?

A study done by Michael A. Page, Maxim Goryachev, Haixing Miao, and peers states that WLCs can be used to improve the sensitivity of LIGO. LIGO currently uses photons (for very constant speed at which ...
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How can a black hole stop light from being emitted when all observers see light traveling at the same speed? [duplicate]

Quite literally every science show talks about black holes with a similar phrase: so dense that nothing, not even light, can escape. Let's say I am in space a safe distance from an object. I drop an ...
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Flux Density Unit Conversion [closed]

I am confused how to convert from ${\rm cm^{-2}\,s^{-1}\,Å^{-1}}$ to ${\rm erg\,cm^{-2}\,s^{-1}\,Å^{-1}}$. How do I do that?
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Can massive objects pull photons into existence?

When a photon tries to leave a black hole, it is redshifted until the wave length is infinite and the photon disappears(?). Could this also happen the other way round, that a (non existent) photon ...
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Does a photon need to have EXACTLY the right energy to be absorbed by a gas molecule?

From an answer to this question, https://physics.stackexchange.com/questions/281660/how-does-an-electron-absorb-or-emit-light, Absorption of a photon will occur only when the quantum energy of the ...
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Does photon capture in a black hole (or any other "very compact" object) reduce the luminosity/photon flux from its self isotropic emission?

I don't know if this is even a feasible question or if I have a point in asking so. Let's say we can model the radiation coming from a very compact object, such as a BH with an accretion disc or any ...
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3 votes
2 answers
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Do objects lose momentum as space expands

As far as I know, photons' wavelengths can be considered increasing as space expands, making them lose energy and momentum. Does the same apply to physical objects? I understand a photon's speed is ...
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Why does the Hubble flow does not carry photons with it?

I have this naive question. We know that the expansion of the universe "takes" or "carries" the galaxies with it, separating them, but this doesn't apply to photons. My guess is ...
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6 votes
1 answer
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Milky Way as seen by the human eye: where exactly do those photons come from?

I'm asking here about the diffuse glow seen by the human eye, when looking at the Milky Way. Where do those visible photons come from exactly? the surface of a star? starlight bouncing off something ...
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43 votes
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Are photons aged?

If a star is at a distance of one lightyear, how old are its photons when they reach earth (from the photons’ perspective)? If time dilation is near zero at light speed, can we assume that the light ...
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Does a photon honor the causality principle?

We know that the faster you move, the slower your time is perceived from an external observer and the space along the direction of the movement shrinks. Photons, having no mass, move at the speed of ...
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2 votes
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Does The ISW Effect Predict Net Redshift Over Distance?

The Integrated Sachs–Wolfe (ISW) effect is concerned primarily with the study of the Cosmic Background Microwave Radiation (CMBR), but seems to demonstrate that photons passing through voids suffer a ...
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Can a change in the density of interstellar and intergalactic quantum fields affect the Redshift of photons?

Using our solar system's heliosphere as an analagy to what is happening in our galaxy and even the universe as a whole, can light redshift with changes in quantum fields? The universe is constantly ...
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7 votes
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Understanding The Fluctuations In The CMB Maps

If I'm understanding this correctly the fluctuations in CMB are a result of the "last scatter" of photons when electrons joined together with nuclei that before this formed plasma. CMB is among other ...
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1 vote
1 answer
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What would we notice if the Sun stopped fusing atoms? [duplicate]

(This question was stimulated by Would we have more than 8 minutes of light, if the sun "went out"?) According to this answer, the "Sun has enough gravitational potential energy to supply ...
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58 votes
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Would we have more than 8 minutes of light, if the Sun "went out"?

The common theory is, that if the Sun "shut down", we would see the light for eight more minutes (the time that it takes the photons to reach the Earth). However recently I have read that ...
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6 votes
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Is the resulting light from a supernova a product of photons bouncing around in the Sun?

I was thinking about how photons formed in the centre of the Sun take quite a long time to exit the surface. And it occurred to me that at the end of a star's life (during a supernova, given that it's ...
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8 votes
1 answer
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Universe is expanding, why doesn't time expand with it?

Reading this response When the universe expands does it create new space, matter, or something else? I understand Universe is not expanding like if it is stretching its space, but it is actually ...
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-1 votes
1 answer
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Mass of Photon and Black holes [duplicate]

The gravity caused by a black hole is said to be so strong such that even light(photons) can not escape from it. since gravity exist only in between objects with mass, How does a black hole attract a ...
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6 votes
3 answers
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Can't pulsars and stars be used for gravitational wave measurement?

Suppose that we collected photons from a distant star, and they arrive regularly at 15 photons every microsecond onto a CCD, when a gravity wave bends space time, wouldn't the regular 15 photons graph ...
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4 votes
1 answer
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Can a photon have a stable orbit around a black hole?

Can a black hole free from an accretion disk collect photons in the photon sphere in a prolonged stable orbit? Could enough photons be in orbit to shade the actual black hole with light? Would a ...
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4 votes
1 answer
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Does Time Exist for Photons? [closed]

If time slows down the closer you get to the speed of light, does it follow that time does not exist for photons. Do photons - even if they travel across billions of light years of space - arrive at ...
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4 votes
1 answer
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Can light be trapped in orbit?

Could rays of light be ever trapped in a constant orbit around a black hole if approached from a certain angle ? Like light hitting a glass or liquid with critical angle.
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How does the size of a naked black hole effect its photon sphere?

What effect does the size of a black hole have on the size or density of the photon sphere and it's proximity to the horizon? For example: A person is in space looking at 2 black holes, one of them ...
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20 votes
3 answers
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Speed of light in a black hole

If I had a directional photon-emitting source and placed it inside a black hole pointing upward and out towards the visible universe, I assume the photons traveling at the speed of light would slow ...
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4 votes
1 answer
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minimum size for a black hole to capture a photon

If a photon is moving past a black-hole, what is the minimum size of the black-hole that will capture the photon and prevent the photon from going onto orbit around the mass? Do black-holes exist that ...
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2 votes
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Question about finding energy density of a fermionic-bosonic gas

We know that energy density is given by this formula: $$u = \frac{1}{V}\int_0^\infty\epsilon_pf(\epsilon_p) g_s V/h^3 4\pi p^2 dp$$ Where $\epsilon_p=pc$ for relativistic particles. also $f(\...
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2 votes
1 answer
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Based on the smallest number of photons that can deliver information about a star, what is the largest size of the universe?

I was watching a summary video about the Banach-Tarski paradox and it led me to a question. If I (a) assume the universe is infinite and (b) assume it is possible to receive a single photon of light ...
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1 vote
0 answers
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How long would it take to collect a certain amount of photons? [closed]

So, I've received this question to solve, it's not a very advanced one, though advanced enough to cause headaches. The situation is as follows: Say, you are observing with a telescope with an ...
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1 vote
1 answer
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Is the CMB the photons that were created at the birth of the atom?

Is the CMB that we see the same, unchanged energy from this moment? Does the radiation of the CMB exist as Photons and are we only witnessing the photons that have not been absorbed or destroyed? Will ...
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What does less than one count from an x-ray detector mean? (Swift BAT detector)

I'm reading a paper about a recent x-ray burst from a suspected magnetar (A. Dai et al 2016) where they show a light curve of a burst that lasted about 10ms. (Their figure 1). The value of count rate ...
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2 votes
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When does oscillation of interplanetary plasma occurs?

When does oscillation of interplanetary plasma occur? When and what are the reasons of the excitation of this plasma that makes it oscillate? Does it oscillate when is not excited? Can extremely ...
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1 vote
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Do astronomers measure radio waves absorption to know the shape of a celestial body? [closed]

I do not have much knowledge about radio astronomy. I know that astronomers know an objects' shape by measuring the reflected photons that reach radiotelescopes, but can they measure also the absorbed ...
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4 votes
2 answers
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Energy carried by solar wind

What are the velocity, mass, and charge distribution of the solar wind. Near the earth within the magnetosphere in the ecliptic Near the earth but outside the magnetosphere in the ecliptic Outside ...
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1 answer
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Has the velocity of photons coming from black holes already been measured?

Has the velocity of photons, which are coming from black holes, already been measured? I am not aware of such measurements. The reason for the question is the following: If space-time near black ...
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-1 votes
2 answers
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Plausible? Brown Dwarfs are rogue celestial bodies because they absorb all light due to their thick layer of matte black soot [closed]

My theory of why Brown Dwarfs are the rogue celestial bodies that travel through galaxies without a set course. My first theory would be their matte black in color due to a layer of soot.Light does ...
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7 votes
3 answers
3k views

How does gravity interact with a photon?

If photon is mass-less and gravity can interact only with matter, then how does gravity alter the trajectory of light?
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3 votes
1 answer
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Do neutrinos have as much information as photons do?

If neutrino detectors keep improving so that a fair number of neutrinos can be observed, would they be as informative for astronomy as photons are? They are of course a very valuable complement to ...
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4 votes
4 answers
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What happens to photons that don't interact with something?

Say a photon left one of the first stars ever created in our universe. This photon has been traveling for 13+billion years through the vastness of space without ever hitting anything. Sure, it's ...
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