There's plenty of obstacles preventing us from leaving our destruction behind besides our garbage. Not even the likes of Elon is going to escape. However they will not stop looking for a way. Quantum mechanics/physics will not open the way as many here can attest to.
Well, yes it does, it's just that "energy as we know it" (say, a photon of light or a photon of x-rays) has a hugely less mass equivalent than the mass of "mass as we know it," an atom or a neutron. So light (as we know it) isn't going to have a "measurable" gravitational field.
Perhaps a huge amount of light, maybe from a supernova, has a "measurable" gravitational field, but if you're close enough to measure it, you've surely got other things to worry about.
The E=MC^2 equation tells us a little mass is equivalent to a lot of energy, and so likewise a lot of energy is only equivalent to a little mass. It should be easy enough to calculate the mass equivalent of a photon (at a particular wavelength/energy level), and then easy enough to calculate the downward force on the photon at the Earth's surface due to Earth's gravity. Such calculations would of course use scientific notation, as it's gonna be quite small.
A photon has momentum but no rest mass for all intents and purposes. It gets ‘bent’ by following the curvature of space time, but it doesn’t interact gravitationally with matter ie you can’t use the classic Newtonian relationship to describe its behavior in the presence of a mass - you have to use Einstein’s field equations for that.
Yes indeed.
In Newton's theory of gravity, the gravitational force only affects objects with inertial mass. Inertial mass is the resistance to acceleration given by the m in m = F/a. Photons have no inertial mass as they have no resistance to acceleration - they always travel at the fastest possible speed through space.
In Einstein's general relativity, matter warps spacetime. This means that objects travelling in straight lines take different paths because of the curvature of spacetime. This affects matter with inertial mass, but it also affects photons.
Neither do photons have relativistic mass. Since they never come to rest, they can't be considered to have rest mass. Without a rest mass, the mass of a photon can’t be increased like other relativistic masses, and that's why a photon can travel at the speed of light without having infinite mass.
This has been covered earlier in the thread.
The famous Compton Scattering experiment shows that photons have momentum.
This was one of the key pieces of evidence physicists used to settle the dispute as to whether light behaved like a particle as well as sometimes like a wave.
Compton Scattering
More on photon momentum - just for you, Pete! 😎
Einstein's general energy equation calculates the energy of a particle in terms of its momentum, p and its rest mass, m(rest)
E^2 = p^2c^2 + m(rest)^2c^2 where c is the speed of light in a vacuum.
Now, photons don't have rest mass, so the equation becomes E^2 = p^2c^2 or more simply E = pc
Hence the expression for the momentum of a photon is p = E/c
The expression shows that the higher the energy of a photon, the greater its momentum.
Einstein's general energy equation calculates the energy of a particle in terms of its momentum, p and its rest mass, m(rest)
E^2 = p^2c^2 + m(rest)^2c^2 where c is the speed of light in a vacuum.
Now, photons don't have rest mass, so the equation becomes E^2 = p^2c^2 or more simply E = pc
Hence the expression for the momentum of a photon is p = E/c
The expression shows that the higher the energy of a photon, the greater its momentum.
The reason I'm questioning it here is because teaching texts I've found point to the Solar Wind causing the tails of comets to always trail away from the Sun citing it as evidence of photonic momentum. But the Solar wind has mass as it's not made up of strictly photons.
The solar wind is made up of matter particles.
"The solar wind is a stream of charged particles released from the upper atmosphere of the Sun, called the corona. This plasma mostly consists of electrons, protons and alpha particles with kinetic energy between 0.5 and 10 keV." - Wikipedia.
"The solar wind is a stream of charged particles released from the upper atmosphere of the Sun, called the corona. This plasma mostly consists of electrons, protons and alpha particles with kinetic energy between 0.5 and 10 keV." - Wikipedia.
Here's a nice article on solar sailing and how it utilises photon momentum:
What is Solar Sailing? | The Planetary Society
What is Solar Sailing? | The Planetary Society
But would a solar sail be affected by the solar wind?
The answer is no.
"Solar sails fly on photons, whereas the solar wind is made up of different ionized particles ejected by the Sun. These particles move slower than light and create a force that is less than one percent as strong as light pressure."
Learning all the time! 😀
The answer is no.
"Solar sails fly on photons, whereas the solar wind is made up of different ionized particles ejected by the Sun. These particles move slower than light and create a force that is less than one percent as strong as light pressure."
Learning all the time! 😀
Comets actually have two tails.
One tail is formed by the charged particles in the solar wind and the other by radiation pressure (photonic momentum).
Beautifully illustrated here: Cometary Tails | COSMOS
I dont think echidnas have two tails, but the males do have a four headed reproductive organ.
I had to rescue an echidna a few months back, It had got stuck up our driveway and was at risk of becoming roadkill.
Because of its spines, I had to roll it over on its back, onto a tarpaulin and carry it back into the bush ... very cute animals 🙂
I had to rescue an echidna a few months back, It had got stuck up our driveway and was at risk of becoming roadkill.
Because of its spines, I had to roll it over on its back, onto a tarpaulin and carry it back into the bush ... very cute animals 🙂
My primary study this week has been "The Sun". Not the star, but the newspaper... 😀
The horseracing section on Aug 20 confidently announced that "Winter Power" will "power" home in the York Nunthorpe stakes at 15.35!
UK & Ireland Results - Horse Racing - BBC Sport
And it did at 9-1! 😱
Unhappily I was on a couple of hopelss Nags called "Golden Pal" and "Chipotle".
Golden Pal was not my Pal, and Chipotle went to Pot in Sun terms. 😡
Ah well. Mystic Meg explained all in the Horoscopes:
Ah right. Unlucky at horses, lucky in love! 🙂
Finally, the two-speed crossword. Caught my physics interest.
Cryptic Clue 10: "Body in space time to arrive first (5)"
Short Clue 10: "Tailed Orbiter (5)"
Fifth letter T, because 3 Down is "Midge (4)" which I made as GNAT. 😎
I leave that for the interested student. But must correct you guys. Comets have three tails, AFAIK!
The horseracing section on Aug 20 confidently announced that "Winter Power" will "power" home in the York Nunthorpe stakes at 15.35!
UK & Ireland Results - Horse Racing - BBC Sport
And it did at 9-1! 😱
Unhappily I was on a couple of hopelss Nags called "Golden Pal" and "Chipotle".
Golden Pal was not my Pal, and Chipotle went to Pot in Sun terms. 😡
Ah well. Mystic Meg explained all in the Horoscopes:
Mystic Meg said:
Ah right. Unlucky at horses, lucky in love! 🙂
Finally, the two-speed crossword. Caught my physics interest.
Cryptic Clue 10: "Body in space time to arrive first (5)"
Short Clue 10: "Tailed Orbiter (5)"
Fifth letter T, because 3 Down is "Midge (4)" which I made as GNAT. 😎
I leave that for the interested student. But must correct you guys. Comets have three tails, AFAIK!
This was explained in my link (did you open it?). Cometary Tails | COSMOS
Switch that in the direction of Uranus! 😀
P.S. Welcome back!
I saw his presence on other threads, so knew he was alive and kicking.
It's so good to have him back, I've missed his geometrical images! 😉
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