New Quantum Theory Separates Gravitational and Inertial Mass | Hacker News Reader

New Quantum Theory Separates Gravitational and Inertial Mass

technologyreview.com

25 pointssoundsop10 comments

err, so by initially assuming that something under the influence of a potential has a mass M, and calculating the Hamiltonian comes up with a proportionality constant of sqrt(M) means that the potential energy of the system is proportional to the sqrt of the mass of the bound object, all things being equal, not that the equivalence principle is broken.

okay typos above aside i just read their paper. it's good work.

they solved a few well known, relatively simple quantum mechanics problems, in college (from the griffiths intro to quantum mechanics book) these problems are usually solved by talking about an electron in an electric potential.

these fine scientists solved a simple quantum mechanics problem not using an electric potential, but using a gravitational potential. the solution ends up resulting in two dimensionless constants that define the particulars of the solution that are measurable. in solving the equation of a they kept separate the inertial mass and the gravitational mass, and the two measurable constants are expressed in such a way in the setup that they are considering such that by measuring these two constants the inertial mass and gravitational mass may both be solved for (two equations, two unknowns).

they are proposing that this is a way of investigating experimentally the distinction if any between these two quantities.

also the appendix was really complicated and it was very hard to follow

I think a quote from Feynman is apt. "I think it is safe to say that no one understands Quantum Mechanics." (Richard Feynman)

My understanding of the article is this, simple yet hopefully useful.

Einstein and many others in the past assumed and observed that the inertial mass is always equal to the gravitational mass because no measurement has or could tell them apart.

Like the break down of classical mechanics at small scales, so too does this assumption, or so this papers calculations predict. In fact the calculations suppose a situation in which you could measure, through "atomic spectroscopy", a difference in these masses.

One must remember this is in the QM world, the size scale of atoms and mass scale of electrons, not with "classical" sized things.

Here's an interesting implication:

Normally objects fall at the same speed no matter how heavy because while the attraction (force) is proportional to the [gravitational] mass, the acceleration is anti-proportional to the [inertial] mass, and the two cancel out.

But if the two are different then a heavier object would fall faster than a lighter one. (Or vis versa.)

I have a suspicion that this would violate conservation of either energy or momentum, but I'd have to think about it more.

Basically if you drop one big object and measure the speed, then compare it to dropping two object each half the size. The big one ends up at a faster final speed than the two half sized one, and that violates both conservation laws.

I don't think that's true. You can only observe that inertial mass is not equal to the gravitational mass if you have two objects of different material with different values for inertial mass/gravitational mass. If the big and the two half sized objects are made of the same material then a different inertial mass just corresponds to a different gravitational constant G.

    Mathematically let m_g be the gravitational mass and m_i be the inertial mass. 
    We have F = m_i*a and F = G*m_g*M_g/r^2. 
    So we have a = G*m_g/m_i*M_g/r^2. 
    Now m_g/m_i is the same for the big object and for the half object.
    We can absorb it into the constant G and end up with a = G'*M_g/r^2.
    Conclusion: the big object and the half object have the same speed.

I hope this opens the door to E.E. "Doc" Smith-style "intertialess" drives. There would still be the weirdness of time dilation, but it would be possible for people to travel to distant stars and back again.

Just being able to have matter that has gravitational attraction and little or no inertia or vice versa doesn't open the door to inertialess drives. To do that, you'd need negative inertia to cancel out the inertia of payload and bits of spacecraft that have inertia. And I don't see anything in the article to suggest that there was any hope of that. In fact, I'm not sure how this would be useful unless you could turn gravitational attraction on and off. If you could do that, perhaps you could rob the mass energy of the one or both of the bodies to create energy? It would basically function as a mass energy converter. But we're a long way even from a theoretical framework for that.

One step at a time! Before this, I thought we weren't sure those two were even separable.

correct me if i'm wrong... but in order for this to catch hold, we'd need to know why this distinction doesn't have a significant effect in the classical world? e.g. for relativity, we know that time dilation doesn't have a measurable effect because we move at very speeds.

anyone have an idea why this wouldn't show up?

with "very speeds" do you mean very low or very high? It kind of makes a difference here...

very low, sorry.

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