Milky Way’s Black Hole Just Flared, Growing 75 Times as Bright for a Few Hours

Re:Milky Way’s Black Hole Just Flared, Growing 75 Times as B... by teddyh on Wednesday August 14, 2019 @04:09AM (#20693571)

A shadow isn’t actually a thing. It’s an image, like a mouse pointer. If I had a sufficiently large screen, and I made the mouse pointer jump (by setting its position) to the other end of the screen, I could calculate its speed and make that number higher than the speed of light. But has anything actually moved? No it hasn’t, because a mouse pointer, like a shadow, is only an illusionary image of a thing, not an actual thing.

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Re:Milky Way’s Black Hole Just Flared, Growing 75 Times as B... by close04 on Wednesday August 14, 2019 @06:02AM (#20694035)

An absence of something can only be defined relative to that something and never taken just by itself. So a shadow only exists as a function of light (no light) or a consequence of the absence of light. So it would not travel faster than light in a way that can carry additional information.

Quantum entanglement works faster than light but cannot carry any information. As such the speed of causality (and implicitly of light) is still the real limit.

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Re:Milky Way’s Black Hole Just Flared, Growing 75 Times as B... by pmohun on Sunday August 18, 2019 @02:31PM (#20731953)

Thanks for this clarification. I have been wondering about this for awhile and your explanation helped a lot.

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Re:Milky Way’s Black Hole Just Flared, Growing 75 Times as B... by marcus_holmes on Wednesday August 14, 2019 @12:53PM (#20697394)

from the point of view of someone in the shadow, and subsequently not in the shadow, the speed of light is still the limit. If the light source is 1LY away, it will take 1LY for me to notice that I am no longer in shadow, regardless of how fast the shadow moves. There's no way of measuring the shadow movement that isn't limited by the speed of light.

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