The photon only ever transfers a small amount of its momentum to the solar sail due to its incredibly minuscule mass with respect to the sail. This is the main reason photon propulsion is so inefficient.
Quote from: dustinthewind on 02/24/2016 05:14 pmThe photon only ever transfers a small amount of its momentum to the solar sail due to its incredibly minuscule mass with respect to the sail. This is the main reason photon propulsion is so inefficient.No. The photon transfers a very small amount of its energy to the solar sail due to its incredibly minuscule mass with respect to the sail. you say 'Tomato', I say 'Tomato'... Its momentum is, to first order, completely reversed (assuming a reflective sail) and thus it transfers twice its original momentum to the spacecraft. That is as good as you can get. Chasing the total amount of energy is a fool's errand; kinetic energy and collision mechanics simply don't work that way. You don't think 2 ships with mirrors and light reflecting between them is a good idea? https://en.wikipedia.org/wiki/Photonic_laser_thrusterIf you manage to get the solar sail to absorb 100% of the photon's energy, you've got a perfectly plastic collision and your momentum transfer is halved. Virtually all of the absorbed energy is lost as heat.We are again talking about a perfectly elastic collision. http://hyperphysics.phy-astr.gsu.edu/hbase/elacol.html
you say 'Tomato', I say 'Tomato'...
You don't think 2 ships with mirrors and light reflecting between them is a good idea?
QuoteIf you manage to get the solar sail to absorb 100% of the photon's energy, you've got a perfectly plastic collision and your momentum transfer is halved. Virtually all of the absorbed energy is lost as heat.We are again talking about a perfectly elastic collision.
If you manage to get the solar sail to absorb 100% of the photon's energy, you've got a perfectly plastic collision and your momentum transfer is halved. Virtually all of the absorbed energy is lost as heat.
Correct on no net acceleration, however, the cavity has moved a bit having both accelerated and then decelerated. This is still the first example where the photon recovers its original wavelength which is (blue shifted) with respect to its previous red shift but technically it just recovers its original wavelength. We are dealing with a perfectly elastic photon so I should say we are dealing with a superconductive cavity. The frame I am considering is a frame that is independent of the cavity or the photon. Originally, it was stationary with the cavity. Sort of a lab frame. The wall that first welcomed the photon is moving away from that frame when re-emitting the photon so I consider it red-shifted as well as being red-shifted having imparted some of its energy into the cavity.[...]mmm, maybe I didn't clarify early on that the stipulation was that the photon was perfectly elastic. A real photon of course will also generate waste heat [...] For being perfectly elastic all the energy goes into the ballistics and is converted into momentum (ideal assumption).
The trick is finding some method of manipulating the effective mass of a photon.
Quote from: dustinthewind on 02/25/2016 01:00 amyou say 'Tomato', I say 'Tomato'...Momentum and kinetic energy are not interchangeable. If you don't understand this, you need to go away and study mechanics until you do.Please remember that momentum is a vector. A very small object bouncing elastically off a very large object comes away with nearly the same absolute value of momentum in the centre-of-mass frame, but it's in the opposite direction. Thus the momentum transferred to the large object is nearly twice what the small object originally had. Its kinetic energy is of course a scalar, and doesn't change much. (And of course all of this is out the window if you're using a different reference frame.)Dustinthewind: If the ratio of energy exchanged in a collision is very small for the large object and almost 100% for the photon then the absolute value of the photons momentum is also going to change very little hence my statement, "you say 'Tomato', I say 'Tomato'..." A change in energy corresponds to a change in absolute momentum. Momentum is conserved and so is energy. Quote from: dustinthewind on 02/24/2016 05:14 pmThe photon only ever transfers a small amount of its momentum to the solar sail due to its incredibly minuscule mass with respect to the sail. This is the main reason photon propulsion is so inefficient. ...Quote from: 93143 on 02/24/2016 10:34 pmNo. The photon transfers a very small amount of its energy to the solar sail due to its incredibly minuscule mass with respect to the sail. Its momentum is, to first order, completely reversed (assuming a reflective sail) and thus it transfers twice its original momentum to the spacecraft. That is as good as you can get. Chasing the total amount of energy is a fool's errand; kinetic energy and collision mechanics simply don't work that way....Dustinthewind: It is not as good as you can get. The photon has a very small relativistic mass so the energy/momentum exchange is almost nothing. The photon escapes with most of its energy/momentum in a reflection.QuoteYou don't think 2 ships with mirrors and light reflecting between them is a good idea?That's a totally different idea; the one ship is using the other ship, not the light itself, as reaction mass. The laser beam in that scheme is just a means of coupling the two massive objects, and the efficiency gain is entirely a function of photon recycling - they make multiple bounces, magnifying the thrust on both vehicles equally and in opposite directions. It has nothing to do with "sucking the energy out of the light"; the energy is from the other spacecraft. You can't reduce the scheme to just one massive object without having to rely on the photons themselves as reaction mass, and if you're relying on light as reaction mass you cannot exceed the efficiency of a photon thruster.Dustinthewind: Lets talk about the one ship using the other ship. The mirrors have infinite Q and the light is perfectly collimated. The light is between the 2 mirrors and the ships aren't moving as they are attached. There is a force but no red-shifting of light. As soon as the ships are released and they starting moving away from each other, we get red shifting. We get red-shifting because F.dx = energy and that energy is coming from the light (energy conserved). Now lets take our ships and push them back together. They are now working against the force and light should be being blue shifted. F.dx=E again we are storing energy in the spring. This form of propulsion is efficient because the photons are not escaping with all their momentum. It is draining the energy out of the photons efficiently. They are getting better thrust than a photon rocket by draining the energy out of the photon by elastic collisions and not letting that energy escape, like a solar sail does. My method also uses elastic collisions to do the same but it's still to be seen if there is any real way to modify the relativistic mass of a photon.QuoteQuoteIf you manage to get the solar sail to absorb 100% of the photon's energy, you've got a perfectly plastic collision and your momentum transfer is halved. Virtually all of the absorbed energy is lost as heat.We are again talking about a perfectly elastic collision.I already covered that. In a perfectly elastic collision between a very small mass and a very large one, the energy transfer is very small. Plasticizing the collision results in more energy transferred, but it is not bulk kinetic energy - it's heat, or strain energy, or acoustic energy, or something else frame-independent. The bulk kinetic energy transfer is at a maximum in a perfectly elastic collision, and it's still minuscule in the centre-of-mass frame of reference.
The photon only ever transfers a small amount of its momentum to the solar sail due to its incredibly minuscule mass with respect to the sail. This is the main reason photon propulsion is so inefficient. ...
No. The photon transfers a very small amount of its energy to the solar sail due to its incredibly minuscule mass with respect to the sail. Its momentum is, to first order, completely reversed (assuming a reflective sail) and thus it transfers twice its original momentum to the spacecraft. That is as good as you can get. Chasing the total amount of energy is a fool's errand; kinetic energy and collision mechanics simply don't work that way....
As soon as the ships are released and they starting moving away from each other, we get red shifting. We get red-shifting because F.dx = energy and that energy is coming from the light (energy conserved).
Quote from: dustinthewind on 02/26/2016 05:02 amAs soon as the ships are released and they starting moving away from each other, we get red shifting. We get red-shifting because F.dx = energy and that energy is coming from the light (energy conserved).Incorrect. The energy is coming from the two ships. F = -FThe photons are unchanged by their reflection, with respect to a stationary observer. The photons are not red-shifted, they are not blue-shifted. They are just changing direction.That's the thing you need to understand. The photons themselves have not been changed, they have not lost energy, only their direction has been changed. And it's the change in direction that is moving the ships (F = -F) not a loss of energy by the photon themselves....
The energy to move the ship is not coming from the energy of the photon, it's coming from the change-of-direction of the energy of the photon. ...The photon has 100 scalar units of energy. It is moving from left to right, so it has 100 vector units of energy to the right.The photon has 100 scalar units of energy.
Quote from: Paul451 on 02/26/2016 03:27 pmThe photons are unchanged by their reflection, with respect to a stationary observer. The photons are not red-shifted, they are not blue-shifted. They are just changing direction.How then do you rectify that a radar gun measures a cars velocity by the change in wavelength of the emitted light. The gun exist in the stationary frame that the photon was emitted in, and if it is as you claim, it appears the photon when returning, will have no change in wavelength to indicate if the car is moving either away or towards the radar gun.
The photons are unchanged by their reflection, with respect to a stationary observer. The photons are not red-shifted, they are not blue-shifted. They are just changing direction.
Is it possible momentum is conserved in absolute but not necessarily direction?
Quote from: dustinthewind on 02/29/2016 02:20 am Is it possible momentum is conserved in absolute but not necessarily direction?No, momentum is a vector. It inherently has both magnitude and direction. It is not like kinetic energy which is only a scalar. But even though Kinetic energy is a scalar it is frame dependent which means its value depends on who is looking.
Quote from: ppnl on 02/29/2016 04:31 amQuote from: dustinthewind on 02/29/2016 02:20 am Is it possible momentum is conserved in absolute but not necessarily direction?No, momentum is a vector. It inherently has both magnitude and direction. It is not like kinetic energy which is only a scalar. But even though Kinetic energy is a scalar it is frame dependent which means its value depends on who is looking.Right, that is what I would think too and I can't think of any natural systems that would violate it.
If the Woodward concept works then it almost implies it may be possible to redirect momentum.
Unless I am mistaken but at the moment, it sure seems that way. I mean the simple device they have at the top of this link seems to imply a re-direction of momentum: https://en.wikipedia.org/wiki/Woodward_effect .
I have noticed the cavity I proposed that modifies the mass of light also re-directs the momentum. I think it is a property that is at the heart of the Mach-effect/Woodward effect concept.
Quote from: dustinthewind on 02/29/2016 04:53 amQuote from: ppnl on 02/29/2016 04:31 amQuote from: dustinthewind on 02/29/2016 02:20 am Is it possible momentum is conserved in absolute but not necessarily direction?No, momentum is a vector. It inherently has both magnitude and direction. It is not like kinetic energy which is only a scalar. But even though Kinetic energy is a scalar it is frame dependent which means its value depends on who is looking.Right, that is what I would think too and I can't think of any natural systems that would violate it.No system can violate it. And that fact isn't a physical fact so much as a mathematical fact. You would have to rewrite physics.Quote If the Woodward concept works then it almost implies it may be possible to redirect momentum.Another way to say "redirect momentum" is "violate conservation of momentum." As long as you understand that then explore the possibilities all you want.Dustinthewind: By re-direct momentum I am saying not to change the absolute value of the momentum but to change the direction which in effect is a violation but re-direct implies not changing the value.QuoteUnless I am mistaken but at the moment, it sure seems that way. I mean the simple device they have at the top of this link seems to imply a re-direction of momentum: https://en.wikipedia.org/wiki/Woodward_effect . I really can't make much sense of anything on that page.Dustinthewind: The device at the top, right hand side, that changes mass and the pulls it self together like an accordion. It then transfers energy to the other side, changing its mass, and then expands each time pushing in one direction. How does a device that vibrates and has zero momentum, (if it doesn't transfer mass), push it self in such a manner with out propellant? It implies a re-direction of momentum during the expanding/contracting phase. QuoteI have noticed the cavity I proposed that modifies the mass of light also re-directs the momentum. I think it is a property that is at the heart of the Mach-effect/Woodward effect concept. As I said above you cannot change the mass of a photon. If you could it would be an immediate and obvious violation of conservation of momentum. You may as well be invoking invisible blue fairies. Or you could try this:http://star.psy.ohio-state.edu/coglab/Miracle.htmlDustinthewind: If changing the mass of a photon/object could give us such an ability as to re-direct momentum eliminating the need for a propellant, I think it would at least be worth considering if it were a possibility, considering the rewards. Some things in the past that were considered blue fairies/impossible were later found to be possible so why not keep an open mind? I read some where, superconductors make photons massive objects, and when light enters a dielectric it slows down. What if light slows down in a dielectric because its effective relativistic mass increases and momentum is conserved? URL: Mass change of dielectric media induced by propagation of electromagnetic waves by C.Z. Tan
Quote from: ppnl on 02/29/2016 07:38 amQuote from: dustinthewind on 02/29/2016 04:53 amQuote from: ppnl on 02/29/2016 04:31 amQuote from: dustinthewind on 02/29/2016 02:20 am Is it possible momentum is conserved in absolute but not necessarily direction?No, momentum is a vector. It inherently has both magnitude and direction. It is not like kinetic energy which is only a scalar. But even though Kinetic energy is a scalar it is frame dependent which means its value depends on who is looking.Right, that is what I would think too and I can't think of any natural systems that would violate it.No system can violate it. And that fact isn't a physical fact so much as a mathematical fact. You would have to rewrite physics.Quote If the Woodward concept works then it almost implies it may be possible to redirect momentum.Another way to say "redirect momentum" is "violate conservation of momentum." As long as you understand that then explore the possibilities all you want.By re-direct momentum I am saying not to change the absolute value of the momentum but to change the direction which in effect is a violation but re-direct implies not changing the value.
Quote from: dustinthewind on 02/29/2016 04:53 amQuote from: ppnl on 02/29/2016 04:31 amQuote from: dustinthewind on 02/29/2016 02:20 am Is it possible momentum is conserved in absolute but not necessarily direction?No, momentum is a vector. It inherently has both magnitude and direction. It is not like kinetic energy which is only a scalar. But even though Kinetic energy is a scalar it is frame dependent which means its value depends on who is looking.Right, that is what I would think too and I can't think of any natural systems that would violate it.No system can violate it. And that fact isn't a physical fact so much as a mathematical fact. You would have to rewrite physics.Quote If the Woodward concept works then it almost implies it may be possible to redirect momentum.Another way to say "redirect momentum" is "violate conservation of momentum." As long as you understand that then explore the possibilities all you want.
I mean the simple device they have at the top of this link seems to imply a re-direction of momentum: https://en.wikipedia.org/wiki/Woodward_effect .
All I am saying is if a projectile with momentum gets trapped in an osculating system and hits one wall giving up 20% of [its] energy but the impact with the other wall only gives back 10% of its energy that the projectile will end up giving its energy to the composite walls in a way that drains its energy.