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Comment by ern | Hacker News Reader

For practical purposes in this case it’s immediate right?

I can do a lot in 8 mins. If you had 8 minute warning for an earthquake, what could you do? Luckily, we get more notice than that now for tornadoes, but 8 minutes is enough time to seek shelter. In 8 minutes, there's plenty of time to ctrl-s on everything, and then close apps and shut down computers.

The problem is communicating to everyone when that 8 minutes starts and how much time is left.

But the point is that we’ll have 15-24 hours, not 8 minutes.

That may be your point, but not the point to which this thread started.

>If you had 8 minute warning for an earthquake, what could you do

That's not how it works. There may be detectable precursors that could actually give warning, but the 8 minutes referenced is the time it takes light from the sun to reach earth. It's immediate in the sense that it is physically impossible to detect that before those 8 minutes have already elapsed and the light is hitting your detectors. You could try to move your detectors closer to the sun to detect earlier, but any signal you can possibly send back to earth goes at the same speed, so it doesn't help.

What if we moved earth closer to sun or more away from sun.

So maybe we are able to detect that at time X there will be solar flares. We know they will be here at X + 8min.

But if we start moving away now from the sun, we will have more time to deal with it.

If it was immediate it should also be immediate even if we moved to 20x distance of the sun, or no?

8 minutes is not something we measured.

It is something we computed. Why? Because there is no way to measure the time it takes for light to get from the sun to the earth. You cannot synchronize a message. There is no "hello". There is no beginning. This is not like firing a starting pistol. We cannot ever know what is happening at the sun with less than 8 minutes of lag. It is a fundamental limit. Even sending a highly robust and extremely precise clock into the sun to measure events, then comparing those events to timelines on earth, would not work. You cannot do it in real time, but even after the fact is pretty much not possible due to relativistic effects.

Good points, but pedantically we can measure such times using a mirror and the round trip of a laser pulse.

This has been done with the moon.

But your points about no 8 minutes of warning stand.

Even more pedantically, you'd be measuring the round trip time from the earth to a mirror located near the sun and back, but not at the sun. Does there even exist a mirror anywhere in this universe that could survive and float on the "surface" of the sun? Does the sun even have a surface? Is there a laser powerful enough to overcome all of the electromagnetic radiation from the sun such that you could actually discern it's signal? Not pedantically, I stand by my assertion that it cannot be directly measured.

What in this World can we truly measure anyway?

It's pointless to talk about that 8 minute warning because the speed of light is effectively the speed of causality. There is no way we can signal back faster than that initial wave of radiation hitting us. There is no way to alert us that that 8 minutes is starting because are theoretical fastest communication will still take 8 minutes to get to us.

But we're not worried about that part of things anyway - it's the mass part of the CME that is the issue.

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