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FastFourierTransform
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### How do you think we can get to Proxima b?

Propulsion Disk wrote:
Source of the post Yeah. I mainly was wanting a propulsion system that doesn't have fuel restrictions...
I'll keep working on it and taking your info into account!

Awesome!! Keep the ideas coming. Good way of handling our skepticism

Propulsion Disk
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### How do you think we can get to Proxima b?

FastFourierTransform wrote:
Source of the post So, as far as your explanation goes I can only see violations of either Newton's 3rd Law, the 2nd Law of Thermodynamics, Coulomb's Law, or a combination of those. Nature is a hard coded restrictor some times.

Yeah. project starshot's thrusters are "photon thrusters" which also violate those laws, because light doesn't have any mass so newton's laws just got broken. It sort of works with the second law of thermodynamics. and of coarse doesn't have anything to do with coulomb's law. so how does it move? I know that it's because light has inertia, but that still shouldn't do anything because light still doesn't have any mass. so how does it push?

JackDole
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### How do you think we can get to Proxima b?

Propulsion Disk wrote:
Source of the post Yeah. project starshot's thrusters are "photon thrusters" which also violate those laws, because light doesn't have any mass so newton's laws just got broken. It sort of works with the second law of thermodynamics. and of coarse doesn't have anything to do with coulomb's law. so how does it move? I know that it's because light has inertia, but that still shouldn't do anything because light still doesn't have any mass. so how does it push?

Light has energy. And according to the formula E = MC² energy is synonymous with mass!
In other words, if photons were slower than light, they would have mass. But because they move with light speed, they are completely energy. But that's why it can still push.
JackDole's Universe 0.990: http://forum.spaceengine.org/viewtopic.php?f=3&t=546
JackDole's Archive: http://forum.spaceengine.org/viewtopic.php?f=3&t=419
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Watsisname
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### How do you think we can get to Proxima b?

Propulsion Disk wrote:
Source of the post Yeah. project starshot's thrusters are "photon thrusters" which also violate those laws, because light doesn't have any mass so newton's laws just got broken.

Photons are massless, but not momentum-less.  They have momentum of p=E/c.

That photons carry momentum and apply pressure is a basic fact of electromagnetism, and can be demonstrated in the lab using lasers and sensitive equipment.

Watsisname
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### How do you think we can get to Proxima b?

I saw you just deleted your post saying that photons can't apply pressure because they are massless, so in case this was still unclear, the reason is that pressure is force per area, and by definition, force is the rate of change of momentum with time.  Photons transfer momentum, therefore they apply pressure.  This is an experimental fact and we can calculate it as well.

The momentum of a photon is p=E/c.  If a light beam has some power P, then the momentum it transfers per unit time is dp/dt = d(E/c)/dt = P/c.  But change in momentum with time (dp/dt) is force!  Therefore the light beam applies a force of P/c if absorbed by a material.  If reflected, then conservation of momentum results in twice the amount of force.

Force per unit area is pressure, (I'm running out of letter P's here, so let's use bold P for pressure), and the pressure applied by the light beam is P = F/A = (dp/dt)/A = (P/c)/A = I/c where I is the intensity (e.g. watts per square meter).  Again double that if reflected.

Propulsion Disk
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### How do you think we can get to Proxima b?

Watsisname wrote:
Source of the post I saw you just deleted your post saying that photons can't apply pressure because they are massless,

What?!  but yeah I understand how the photons work now but does this mean that light pushes oxygen atoms and we just didn't notice all this time? does this mean that light can cause atomic erosion?
Last edited by Propulsion Disk on 27 Jun 2018 06:32, edited 2 times in total.

Watsisname
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### How do you think we can get to Proxima b?

Light scattering off of atoms does impart a force on them, but for visible light on air, the effect is very small and not easily noticeable.  Take for example a 500nm photon scattering off of an oxygen molecule.  The momentum of this photon is 1.3x10-27 Newton-seconds, and if scattered by 180°, then it would change the velocity of the oxygen molecule by about 2.5 cm/s.  This is a very tiny fraction of the average velocity of oxygen molecules in air at room temperature (nearly 500 m/s).

You might think that with so many photons of sunlight streaming in constantly, the effect would build up and blow all the air away, but what instead happens is that because the atoms are also quickly colliding with one another, any additional velocity gained through scattering photons is quickly converted into random (thermal) motions of the atoms and re-radiated as heat.  So no net effect is accumulated.

An example of where the pressure applied by light on atoms does become noticeable is clouds of gas around hot stars.  In those environments the light can be very effective at pushing the surrounding gas away.  Another important example is the stars themselves -- it is literally the radiation pressure supplied by all the photons streaming outward from the core that supports a star against collapsing by its own gravity.

Propulsion Disk wrote:
Source of the post does this mean that light can cause atomic erosion?

What do you mean by atomic erosion?

Propulsion Disk
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### How do you think we can get to Proxima b?

Watsisname wrote:
Source of the post What do you mean by atomic erosion?

Atomic erosion is when atoms get destroyed by pressure. for instance, if you break a wooden board, atomic erosion would happen as you break the board. so pretty much what atomic erosion is when things break apart, when things break, the atoms that join the two parts of the wooden board together get destroyed when you break it. this also happens when you rub on anything, your destroying a few atoms, in fact, when you touch anything you destroy a few atoms. this is the reason we get numb from doing things like that, we are rubbing with our skin and our skin rubs on our nerves which causes atomic erosion on your nerves the most because they're way less dense than our skin is, good thing our body's can heal or we would be numb all over every morning! so now you know that when you touch ANYTHING you actually destroyed it a little, but just a little.

Watsisname
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### How do you think we can get to Proxima b?

You're talking about bonds breaking, not atoms being destroyed.  If a photon breaks atomic bonds it is called photodissociation.  It requires photons of sufficient energy.  For example, ultraviolet photons can dissociate ozone (O3) molecules in the atmosphere.

Sufficiently energetic photons can also eject electrons from atoms.  This is the photoelectric effect and is related to the earlier discussion of the work function for metals.  It typically requires energies of a few electron volts or greater.  For example, the work function for mercury metal is 4.5 eV.

Propulsion Disk
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### How do you think we can get to Proxima b?

Watsisname wrote:
Source of the post You're talking about bonds breaking, not atoms being destroyed.  If a photon breaks atomic bonds it is called photodissociation.  It requires photons of sufficient energy.  For example, ultraviolet photons can dissociate ozone (O3) molecules in the atmosphere.Sufficiently energetic photons can also eject electrons from atoms.  This is the photoelectric effect and is related to the earlier discussion of the work function for metals.  It typically requires energies of a few electron volts or greater.  For example, the work function for mercury metal is 4.5 eV.

Oh yeah your right! well, forget about what I said about "the wooden board," I got them mixed up, but I'm pretty sure that atomic erosion happens when well, atoms get eroded. the starshot's protective coating is made of beryllium copper which is dense enough to withstand atomic erosion, but anyway, yeah I got bond breaking mixed up with atomic erosion, (WHOOPS.)

Propulsion Disk
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### How do you think we can get to Proxima b?

I just double checked and it's atomic PARTICLE erosion so that means that the electrons are what get eroded.

FastFourierTransform
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### How do you think we can get to Proxima b?

Propulsion Disk wrote:
Source of the post I just double checked and it's atomic PARTICLE erosion so that means that the electrons are what get eroded.

Exactly. In the case of starshot you are dealing with so called sputtering. Cosmic rays and stellar wind particles moving through interstellar space can indeed erode the surface of those coatings, but nut by "eroding atoms" but by ejecting them. Even then, the main source of erosion for starshot in interstellar space are particles in scale of dust not in molecular or atomic scale. Dust particles can damage the sail at relativistic speeds but they have calculated that it can be handled (a microscopic hole in the sail is not so important but many could be) by reshaping the sail, building it with self-healing materials or even by clearing the path with the ground-based laser at least for the interplanetary traverse before exiting the solar system.
Photonic sputtering also exists but is a very rare phenomenon and does not play an importat role at all in the erosion of the coating.
It's importat to note that atoms DO NOT erode. I mean, erosion is a very macroscopic concept, it involves the degradation or dilution of matter. You can't apply that concept to atoms. Atoms can be ionized, their nucleai can be split etc.. but an atom is an atom and elementary particles can be separated and the atom as a system can cease to exist but the idea of it been degraded by the effects of time is quite strange. Erosion is the classical phenomen that can be pointed as an example of emergence in complex systems. Atoms are in far away from physical complexity, that's why emergent properties cease to make sense (not only erosion, also temperature and even the row of time as many think).

Mr. Abner
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### How do you think we can get to Proxima b?

Wouldn't actual atomic erosion be fission? I sure hope I don't have any of that going on in my fingertips!

Watsisname
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### How do you think we can get to Proxima b?

I think I would recommend avoiding using the word "erosion" to anything involving atoms, like FFT said.  To apply it to atoms doesn't make much sense and I've never seen it used in the scientific jargon.  Hence my earlier question about what Propulsion Disk was imagining.  All processes involving nuclei splitting, atoms knocked off a material, electrons being removed from atoms, bonds breaking, etc, have other names for them.

Propulsion Disk
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### How do you think we can get to Proxima b?

Watsisname wrote:
Source of the post I think I would recommend avoiding using the word "erosion" to anything involving atoms, like FFT said.  To apply it to atoms doesn't make much sense and I've never seen it used in the scientific jargon.  Hence my earlier question about what Propulsion Disk was imagining.  All processes involving nuclei splitting, atoms knocked off a material, electrons being removed from atoms, bonds breaking, etc, have other names for them.

Yeah I corrected myself on that, I said on my last post that it's atomic PARTICLE erosion which means electrons get eroded by the things in space. I would like to know the names for atoms being knocked off, bonds breaking, you know the stuff you mentioned, also you said that there is another word for "electrons being removed from atoms" other then erosion or ionization so I would really want to know what it is. (PS) I read "atomic particle erosion" on the Wikipedia so if it's not reliable when it comes to science then can you help with the question that I had in "science and astronomy questions?" It would really help.

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