AS an astronomy-obsessed kid in the 1970s, I subsisted on a steady diet of science fiction. It promised a future filled with technological wonders: talking computers, bionic limbs, flying cars. Forty years later, though much of that future has arrived, it’s still missing what I consider its most important ingredient. Sure, we’ve got the iPhone’s Siri, and the Food and Drug Administration just approved a prosthetic arm controlled by signals from the brain — but where are our smooth-gliding flying machines, our Landspeeders (“Star Wars”) and airborne DeLoreans (“Back to the Future”)?
You may think that the absence of such cars speaks to a failure of engineering or distorted incentives in the marketplace. But the humbling truth is that we don’t have these vehicles because we still don’t know, even in principle, how to directly manipulate gravity. Indeed, the cars missing from our skies should serve to remind us that, to a degree rarely appreciated, we have surprisingly poor control over most of nature’s fundamental forces.
full article at I Was Promised Flying Cars – NYTimes.com.
This article points out something I’ve never thought about. That we really only have command of one of the four fundamental forces of nature, electromagnetism. We have a crude limited ability to manipulate the strong and weak nuclear forces, but no ability whatsoever to manipulate gravity. (Although we do understand it well enough for our spacecraft to navigate the interacting gravity of solar system bodies.)
I see this as a reminder of how beneficial a usable theory of quantum gravity might be, whether or not it rises to actually being a theory of everything. Physicists have, of course, been pursuing this for the last several decades. That’s what all the speculative stuff about strings, branes, and the like are about. But I think it’s fair to say that, aside from some mathematical techniques, little reliable knowledge has come of it.
Modern physics appears to be spinning its wheels on this issue. It’s not even clear what empirical investigations might help, although the LHC appears poised to dispense with a lot of theories when it fires up again, principally by burying supersymmetry. (Although the advocates of that theory will likely continue to claim its viability in modified forms for years to come.)
It feels like some new fundamental insight about how the universe works will be necessary to move forward. (Of course, any such insight will have to account for what we already know, something many claiming to have that insight fail to appreciate.)
SelfAwarePatterns 
It is definitely a problem that we don’t have an verifiable understanding of gravity that links it to the other three forces of nature. I’d quibble with Frank in the sense that we can control gravity – it’s just that to create it, we have to shove a bunch of mass together, and even then it’s an incredibly weak force in comparison to electromagnetism.
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Excellent point. It makes me wonder what might be possible if we could ever figure out a way to manipulate the Higgs field.
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Don’t count on quantum gravity enabling us to build flying cars. It operates only in black holes. And manipulating the Higgs field would require enormous energies too
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The basic problem with gravity is that it’s a purely attractive force, so “anti-gravity” is purely an imaginative idea for sci-fi.
But gravity is a weak force and can be overcome relatively easily. Flying is an engineering problem. Birds and insects manage it by being small. Aircraft manage it by being fast. Helicopters manage it by being cleverly designed. What we need is something even more cunning. It’s an engineering problem, not a scientific one.
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No argument that it’s an engineering problem. Science shouldn’t be motivated by specific engineering issues. It should learn whatever it can. Still, we can never know what engineering capabilities could be opened up by a sufficient understanding of quantum gravity.
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We should certainly try to unify quantum mechanics and gravity, however like Steve I think it is unlikely that such understanding will greatly increase our capabilities.
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It’s possible that we’ll get some stargate/FTL/time machine out of it, but not a flying car.
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After giving it some thought, I do have to agree with you and Steve that learning about quantum gravity is unlikely to give us any power over gravity overall. After all, if it manifested at measurable and useful levels on the quantum scale, we would probably already understand it. Still, unlikely is not impossible. I’m sure the 17th century scientists who were just starting to understand electricity had little conception of just how much power if would eventually give humanity.
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