Equation 65 · Part 3 · A Horizon Is a Toll Booth, Not a Loophole

subscript

r_s\approx1.18\times10^{10}\,\mathrm m

subscript

What this part means

The lower label selects a particular version, component, or indexed member of the quantity. For example, x₀ and xₜ can be values at different positions.

Its job in the formula

A subscript distinguishes a version, component, step, or member of a quantity. It does not automatically mean multiplication.

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The passage around this formula

To make this concrete rather than asymptotic, take the mass of Sagittarius A* as measured by the Event Horizon Telescope, M $\approx$ 4 $\times$ 10^6\, $M_\odot$ , giving a Schwarzschild radius $r_s$ $\approx$ 1.18 $\times$ 10^{10}\, $\mathrm m$ and a horizon-scale acceleration factor GM/ $r_s^2$ $\approx$ 3.80 $\times$ 10^{6}\, $\mathrm{m\,s^{-2}}$ [ 14 ] . At a clearance of just one kilometer above the horizon — a distance smaller than a millionth of the horizon’s own radius — f $\approx$ 8.46 $\times$ 10^{-8} and the required proper acceleration is already a $\approx$ 1.3 $\times$ 10^{10}\, $\mathrm{m\,s^{-2}}$ , more than a billion Earth gravities. Even at a clearance of 1.8 $\times$ 10^6\, $\mathrm{km}$ — about fifteen percent of the horizon’s own…

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Learn the underlying idea

A subscript is a label attached below a symbol. It often selects a time step, component, category, or member of a sequence.

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Sources cited in the surrounding passage

[14] First Sagittarius A* Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole in the Center of the Milky Way ↗

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