Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Woodward Effect? Explain, please?

  1. Sep 28, 2008 #1
    Mach Thruster: The Woodward Effect?

    Okay, here's a different idea for "propellant-less" propulsion:


    It's based on some idea by a University of California physicist named James Woodward, who himself preferred to use the term "Mach Effect"


    Basically, his idea was that if you have mass moving at relativistic velocity inside another mass, then the internal moving mass can make itself heavier or lighter depending on how fast it's moving.

    So then if you make the overall system oscillate (surrounding mass), and you time the movements of the inner mass with the oscillations, then you can selectively impart more momentum in one part of the oscillation than in another, for the overall system. This would create a net change in momentum for the system.

    Did anybody catch what I said there?

    Hmm, this one has me scratching my head.

    So where did the extra mass/momentum on demand come from? Well, it came from the relativistic motion of the inner mass. You can switch that motion on or off, depending on which way your overall mass-system is oscillating. If momentum is to be conserved, then where did the difference in momentum go? It went to, umm, space? It went to whatever it is that retards the motion of a relativistically-moving mass. The universe?

    Hmm, tell me, if I lift up a cyclotron that's whirling particles around at extremely high speed, will it feel heavier to me than if I lifted it up while it was turned off?
    Does anybody see what I'm saying here?

    In that sense, is a relativistically-moving mass really a closed system? Or is it somehow interacting with space itself, where space itself can't really be described as closed?
    Last edited: Sep 28, 2008
  2. jcsd
  3. Sep 28, 2008 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Edit: I overlooked something really simple when I wrote this. See #5 for more information.

    I'm pretty sure the total momentum of the inner mass must be 0, at least when you average it over time. Imagine a propeller rotating in a box with a vacuum in it. (In this case you don't need to average over time, but if you instead imagine a ball bouncing between the side walls of the spaceship, perpendicular to the direction of the ship's motion, then you have to).

    You obviously need an energy source to change the speed of the propeller. This energy source is what contributes additional (relativistic) mass to it. The energy source should be located towards the front of the ship, because that will give the ship another push forward every time that energy is transferred to the propeller to speed it up. (Even if the energy source absorbs energy from the propeller when it slows it down, it will always be a smaller amount because of energy loss in the form of heat).

    Now push the box with the propeller in it towards the back of the ship when the speed/mass is high, and push it back when the speed/mass is low. The ship will be pushed forward, and then backward, but the forward push is bigger.

    It sounds like it should work in principle, but it also sounds like it would be the slowest spaceship ever, kind of like a spaceship with a battery-powered flashlight instead of a rocket engine.

    And yes, your cyclotron will feel heavier when the particles inside it are moving around fast. Even if you just heat something up, it will make it heavier.
    Last edited: Sep 28, 2008
  4. Sep 28, 2008 #3
    So are inertial mass and gravitational mass always the same?

    If you have 2 bodies both moving together at some relativistic velocity, will their gravitational pull on each other be greater than if they were both at rest?
  5. Sep 28, 2008 #4


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    There are several threads that deal specifically with that question, and there are people here who have spent a lot of time thinking of good answers for those threads, so I'll leave this one to them. (I would have to do some thinking to give you a good answer, and I don't have time for that right now. I think the short answer to the second question is no).
  6. Sep 28, 2008 #5


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    I have changed my mind. Either I have misunderstood what this "effect" is supposed to do, or it can't possibly work. It's pretty obvious really. Nothing ever leaves the ship, so if the ship moves forward, momentum isn't conserved.
  7. Sep 28, 2008 #6


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    OK, I read a few lines in one of his articles, and he claims that Mach's principle implies that the rest mass of an accelerating object will change. So this is not about relativistic mass at all.

    I haven't tried to understand the argument, but there are references in here (a pdf file) to other articles that present the argument.
  8. Sep 28, 2008 #7

    Jonathan Scott

    User Avatar
    Gold Member

    After reading the patent and some of the other material, in particular the paper "MACH’S PRINCIPLE, MASS FLUCTUATIONS, AND RAPID SPACETIME TRANSPORT" linked from Woodward's web site, I'm extremely sceptical.

    In Special Relativity, all four components of four-momentum (that is, energy and linear momentum) are locally conserved at the microscopic level, with an equation of continuity. This also applies locally within GR, and is thought to apply on a larger scale too although there is some difficulty in describing this in GR because gravitational energy cannot be localized in a unique way.

    It is certainly true that local conservation rules do NOT apply to rest mass, but Newton's law applies to total energy rather than rest mass, so this isn't relevant.

    What may not be immediately clear is that this means that if energy is supplied to something by any means, regardless of whether it is via wires, pipes, axles, fields or whatever, then any change in energy or momentum must flow through that route.

    For example, if you look up "dipole gravity" you'll find that many years ago Eue Jin Jeong had an idea that if you spin up a hemispherical object around its axis of symmetry, you will shift the center of mass slightly along the axis because of relativistic considerations. (This can be better illustrated by considering an axle with two wheels on it of the same mass but different radii, so one gets more rotational kinetic energy than the other as the rotation rate increases). It is true that the center of mass of the system shifts, but if you use Special Relativity to analyze the details of how the torque is applied through the axis, you will find that if the assembly were free to slide along its axis, it would shift to keep the center of mass in the same place, and a force has to be applied to prevent that from happening, so there is no overall shift of the center of mass. (However, Eue Jin Jeong has ignored this analysis and is now apparently trying to profit from this idea).

    Similarly, I think Woodward must be ignoring some part of the energy or momentum flow to achieve his result. For example, it appears that he thinks that there is a loophole related to dm/dt terms in Newton's law. However, this isn't relevant, because the microscopic conservation of four-momentum is exact, and even if the calculations in difficult cases involve extra terms, these cancel out when you consider the flow of energy from one described system to another.

    Similar ideas relating to unbalanced forces in sufficiently complex systems such as gyroscopes have been presented many times before (such as in the "Dean Drive" and ideas from Eric Laithwaite). In each case, a complex calculation appears to show unbalanced terms. However, as four-momentum is locally conserved, any such effect must be due to an incomplete or incorrect calculation, even if it is very difficult to find a specific error.

    This means that if there is any possibility of some propellantless drive, it cannot arise from combining existing physical effects in a new complicated way, as all of those physical effects are known to be subject to the local conservation rules. It can only arise from new physics.
  9. Sep 28, 2008 #8

    Vanadium 50

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor
    2015 Award

    Actually, he's a historian.

    Woodward would argue that momentum is conserved because the entire rest of the universe is being kicked backwards.
  10. Sep 28, 2008 #9

    Jonathan Scott

    User Avatar
    Gold Member

    That's not the way in which momentum and energy are conserved. Momentum components and energy are like a fluid which cannot be created or destroyed but can flow from place to place. There can't be any gaps in between. We sometimes use "action at a distance" models, for example when describing electromagnetic interactions, but these are just a simplification; a more accurate model would show that the energy flows through the field, and that flowing energy has momentum.

    It would be more acceptable to talk about the rest of the universe being kicked backwards if some form of energy and momentum transfer were clearly taking place. A propellant doesn't need to be a material solid; it is possible to propel something by emitting a beam of electromagnetic radiation, and it might even be theoretically possible to do so by emitting a beam of gravitational radiation (I don't know about that one). However, some form of energy has to flow to create a reaction.
  11. Sep 29, 2008 #10

    Vanadium 50

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor
    2015 Award

    Of course not. Like I said, that's his argument.

    The problem, apart from the fact that Woodward's calculation is Just Plain Wrong (it takes the same momentum to stop a the mass that it did to get it going in the first place) is that momentum is conserved locally as well as globally. I can't move the momentum to the "rest of the universe" without applying a force.
  12. Feb 25, 2010 #11
    I suggest reading this long thread at NSF Forums, in special for the many posts by GI-Thruster and Star-Drive (Paul March), both involved at ME-Effect experiments and with Woodward.

    Its worth reading, and they explain it all very carefully.

    I suggest starting at page 6, with the first post by GI-Thruster. When Star Drive starts posting however, is when things get interesting.
  13. Feb 25, 2010 #12
    He actually spammed the physics department student emails awhile back. So I can comment on some of this.

    For those not wanting to delve into it, here are some facts about this theory:
    1) His theory requires non-local interactions (is not compatible with SR and causality)
    2) The "mach" comes from his theory claiming mass is due to the interactions with the rest of the universe (including interactions propagating back in time)

    So, in my opinion, if you want to use this for propulsion, you can pretty safely ignore it.
    If you are interested in it more for theoretical reasons, you can safely ignore it, unless you are okay with accepting all of the above. Since I doubt that is the case, I'm not going to bother commenting further.
  14. Feb 25, 2010 #13
    The short answer is no. The mutual gravitational pull will be less, if the two bodies are moving relative to the observer. To an observer co-moving with the two bodies, the mutual gravitational pull will be the same. This is simple application of SR. If the two bodies moved towards each other faster as you suggest, this would provide a method to detect absolute motion and this would violate SR.
  15. Feb 25, 2010 #14
    have you read the above thread from Nasa Spaceflight and the explanations provided by Paul March?

  16. Feb 25, 2010 #15


    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    Last edited: Jul 22, 2011
  17. Dec 16, 2011 #16
    The idea is that a the mass of the piezoelectric material changes with the square of the rate of change of the energy in the material. You can even make the mass go negative.

    Note: This is a violation of conservation of energy. You can lift an arbitrarily large mass upwards in a gravitational field with an arbitrarily small amount of energy, as only the square of the change in energy wrt time causes the mass change. One can then remove the changing energy that is applied to the capacitor and "drop" the mass (say, with a string on a generator) and obtain a net positive energy output.

    To test this effect of mass change, in 2009 I put a piezoelectric capacitor on a tuning fork and applied a voltage at the resonate frequency of the tuning fork + capacitor device. This would amplify the expected magnitude of the Woodward effect so it could be measured. The experimental design was such that I expected to see the fork vibrate if a changing mass was affected by gravity on the fork. I measured the amplitude of the tuning fork with an inductive sensor and I had worked out the parameters of the fork so I could tell with 2 digit precision what the driving force (the mass change under the force of gravity) was. A "naive" application of the Woodward equation would have been detected, tho' it was argued that the Woodward equation was a difference equation and I was doing it wrong.

    After accounting for the piezoelectric effect itself and for effects of the earth's magnetic field by nulling them out, I could measure no change in mass of the capacitor.

    I found no mass change. Zippo. Nada. Zilch.

    This experiment was done for my master's project under the Guidance of Dr. John G. Cramer at the University of Washington. We did not publish because I more tests were required for verification of the null result. As Dr. Cramer was retiring and I was graduating, I didn't do more testing.

    I would note that there is a math error in the derivation of the Woodward effect's theory. If one uses Sciama's result of (Phi+phi)/c^2 = -1/G, one cannot treat the speed of light as a constant and phi as a variable.

    This experimental result could be disputed by noting that I was checking for a gravitational mass change and not an inertial mass change. The original experimental design (aka "Mach Guitar") checked for an inertial mass change. However, the original experiment couldn't be done as the mass of the capacitor significantly changed the resonate frequency of the Mach Guitar. I mathematically studied the experiment, and found that I needed a guitar "string" as thick as a tuning fork tine.

    This experiment was difficult to construct. I had planned on repeating the experiment to do a statistical study of the results, and to try driving the fork to see if I could detect a change in INERTIAL mass, but personal issues and a lack of a High voltage amplifier prevented me from proceeding. I also was fairly confident in my initial result, and felt it was a bit like beating a dead horse.
  18. Dec 16, 2011 #17
    Why does peer review make a difference between locked or unlocked?
  19. Dec 16, 2011 #18


    User Avatar

    Staff: Mentor

    Click the "Rules" link at the top of any page here and read the section Overly Speculative Posts.
  20. Dec 16, 2011 #19
    Hi Steve,

    Thanks for your great response. Regarding your experiment using a tuning fork resonator, just today I was reading about a novel experiment recently done with a nanomechanical resonator:


    Is it conceivable that an experiment like yours could be re-done at a finer level of precision using a nanomechanical resonator similar to this one?

    Just wondering.
  21. Dec 19, 2011 #20
    regarding Steve´s post, here is GiThruster´s (who is part of Woodward´s mail list and performs a few experiments himself), posted at Talk Polywell forum:



    Paul March answered to that last remark by GiThruster with the following:

    Last edited: Dec 19, 2011
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?

Similar Discussions: Woodward Effect? Explain, please?