hypothetically, if the sun doesn't swallow earths orbit in the "near" future, how long until earth orbit decays enough for us to hit the sun?

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answers:
Ronald 7 say: If the Earth's orbit did fade, it could only fade outwards
If we wait another 4.6 Billion years the Sun will become red and swell out to nearly Mar's orbit
With she Sun losing mass there could be an expansion in the planets' orbits
But Earth will probably be vapourised
We might have moved to Mars by then, which could possibly survive
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Fred say: The Sun is projected to go red giant in some 4. 6 billion years and expand into the orbit of Mars. Earth's degrading orbit is projected to shorten that time by 3 hours and 27 minuets; give or take 7 minutes.
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Raymond say: E = m c^2

The Sun emit energy at such a rate that it turns over 4 million tonnes of matter into energy, every second.
When 4 atoms of hydrogen are fused into one helium atom (plus two positrons and some neutrinos), the total mass of the helium + things is every so slightly less than the original mass of the 4 hydrogen atoms. It is this difference that gets turned into energy.

Things falling into the Sun (dust, comets) is not enough to make up for the loss. Therefore, the Sun gets less massive with time. Earth's orbital energy remains the same over time (there is a small -- very small - gain from the tidal effect of Earth onto the Sun). If Earth keeps the same orbital energy and the Sun loses mass, then our orbit grows outwards.
Not by much, mind you (millimetres per year?).

Earth is not spiraling into the Sun.

In roughly 5 billion years, when the Sun reaches its red-giant phase, its surface may balloon out until the Sun's atmosphere reaches out to our present orbit. IF we are still on that orbit, then the Sun's atmosphere will slow us down (the same way Earth's upper atmosphere is enough to slow down the International Space Station which needs an occasional boost).
IF that happens, then Earth will spiral into the Sun.

By then, though, Earth will not have been suitable for life for a few billion years.
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quantumclaustrophobe say: Actually, with the sun losing mass over time - our orbit is widening just a tiny bit every year.
When the sun begins to die, it'll swell up during the 'Red Giant' phase, and it's possible that the sun's atmosphere will expand wide enough to engulf the Earth; if that happens, Earth will slowly spiral inward due to the added drag, and eventually be ripped apart by tidal forces of the sun's core... Earth will 'rain down' onto the core, and... that will be that...
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poldi2 say: About 2 billion years, but its not that the Earth's orbit will decay its that the sun will expand to engulf Mercury, Venus, and the Earth.
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busterwasmycat say: the earth is moving away from the sun, just like the moon is moving away from the earth. Gravitational attraction involves some "friction" (mostly what we call tidal motion), and this friction slows the rotation of the central object, causing a transfer of rotational momentum to the orbiting object. As a consequence, the object in orbit slowly moves further away. Eventually, the orbiting object will attain a distance where the object gets "Locked" tidally with the center of rotation (eliminates the friction, sends it to 0) and that outward movement stops (the orbiting object appears to stay in the same place relative to a surface location on the central object). With the moon, that would mean that there would be one place where the moon was always overhead.

I haven't seen calculations for the time frame required for a planet to achieve that state, but calculations I have seen for the moon give a ballpark 50 billion years for that to happen. Planets should take much longer than that given the immense difference in mass of planets relative to the sun (moon and earth are similar in mass so the effect is much more rapid).
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Eric say: The Earth does not orbit the sun. The Earth is the center of everything and there's no chance that the Earth and the sun will change position because the Earth is fixed and the sun revolves over and across it.
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Paula say: In trillions of years from now the earth would stop moving away from the sun.

After that it would take quadrillions of years (or even much longer) for the earth to lose enough orbital energy to collide with the sun.

Actually the earth is losing orbital energy right now, but it is overwhelmed by the gain from the sun/earth tidal interaction.

Anyway it is a moot point, because the sun is predicted to vaporize the earth in about 5 billion years.
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Starrysky say: Earth's orbit is not decaying, not getting closer to sun. As the Earth goes around sun a very small bulge in sun's shape slows the Earth's motion. This tidal force applies brakes to Earth. By only 15 cm a year, its orbit moves farther from Sun. Another factor is the sun is losing mass as it converts hydrogen into helium, and blasts a solar wind of particles off its surface. The attraction of gravity by sun to all the planets decreases.
Earth will always get a little farther from Sun in billions of years.
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Nyx say: In about 4 to 5 billion years, the sun will expand outward as it switches from hydrogen to helium fusion. It just might melt Earth.
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WHANKING-WILLY say: Oh dear... Oh, for a moment I was very worried. I thought you meant millions of years and not billions of years.
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CarolOklaNola say: Earth's orbit is actually getting a tiny
bit farther away from the Sun because the Sun is losing mass because of conservation of momentum. Earth is closest yo the Sun RIGHT NOW. Earth is ALWAYS falling toward the Sun, but the Earth has enough velocity to stay in orbit. There is no friction in space to slow Earth down
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