I don't want to worry you, but . . .
You hear the weather forecast, later you tap the barometer, then look out at the hills and see the rain coming. So you take an umbrella.
This is the weather forecast.
It rather depends on what was happening at the centre of the galaxy 23,000 years ago. But if, as expected, it was then drastic, such as the super-dense galactic core routinely sucking the few nearest stars to its bosom, causing a mass flux ejection from it, then there is an oncoming cosmic shock-wave. Any who hope to survive the consequent coronal mass ejections from the sun starting its pass through the galactic plane in December 2012 should take the following to heart for thereafter.
When the initial wave does come, and from the geological record, such occurrences apparently happen regularly each fourteen thousand years or so, one now being somewhat overdue, it will arrive without warning, as it moves at more or less at the speed of light. It is this routine outward pressure that prevents a galaxy from collapsing in on itself. The intervals between the waves depend on a galaxy's size and composition.
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