Slashdot Mirror

← Back to Stories (view on slashdot.org)

Inertial Mass Separate From Gravitational Mass?

Posted by Soulskill on from the what-an-interesting-mass-effect dept.

CPerdue writes with this excerpt from the MIT arXiv blog: "The equivalence principle is one of the more fascinating ideas in modern science. It asserts that gravitational mass and inertial mass are identical. Einstein put it like this: the gravitational force we experience on Earth is identical to the force we would experience were we sitting in a spaceship accelerating at 1g. Newton might have said that the m in F=ma is the same as the ms in F=Gm1m2/r^2. ... All that changes today with the extraordinary work of Endre Kajari at the University of Ulm in Germany and a few buddies. They show how it is possible to create situations in the quantum world in which the effects of inertial and gravitational mass must be different. In fact, they show that these differences can be arbitrarily large."

2 of 405 comments (clear)

  1. Re:what about gradients? by BradleyUffner · · Score: 5, Insightful

    When a body accelerates all its components are accelerated at the same rate.

    Not quite. Acceleration starts at a specific point and "pushes" its way through the object at the speed of sound in the material of the object. If you had a 10 mile long metal bar and were strong enough to shove one end, the other end wouldn't move instantly. Your force would start a compression wave along the metal bar, traveling at the speed of sound though the metal, until it reached the other end. Same with a rocket, the engines apply acceleration at their connection point and the acceleration pushes its way through the materiel. This is why they have to be built out of such strong stuff, it has to be able to withstand the compression forces of the acceleration without fracturing due to stress.

  2. No GR in Article by Roger+W+Moore · · Score: 4, Insightful

    I would think this means we have a basis for making quantitative measurements of what happens where GR and QM collide.

    Not quite. They make no assumptions about GR in the article, what they have done is come up with a way to test one of the assumptions of GR - assuming the article passes peer review, arXiv is just a preprint server. There are too possible outcomes to the test they propose: m_i=m_g or m_i!=m_g. In the first case nothing has changed and in the second case one of GR's core assumptions has been dismantled so GR cannot be a fundamental theory since there is a phenomenon which it cannot explain. Hence QM and GR will never 'collide' because GR will have disappeared to be replaced by something else - possibly something which QM has no problem with.

    My personal guess is that any such experiment will show that m_i=m_g but it will be an interesting test to do and potentially result in a far more accurate test of the equivalence principle.