People are saying that The Pillars Of Creation have been destroyed, and will take 400-500 Million light years to reach us. Can someone explain how do we know it when the light hasn’t reached us?
In: 1444
If you saw a 100 year old picture of a middle aged man you could say with absolutely certainty that he’s dead, right? The same logic applies. That kind of celestial phenomenon has a certain life span and it’s shorter than 400 million years. Therefore we know its something very different now.
Let’s say you see image of a falling glass. You can calculate it will hit the ground in exactly 1 second and you know it will shatter in pieces. If I tell you that this image is from 5 seconds ago, you know that the glass is shattered even if you didn’t see the landing itself.
That’s how Pillars work. We predicted that they will be destroyed in X years and we know that they are less than X light years from us. Thus, their destruction has already occured.
Imagine there are humans 70 light years away. They are sending us audio and video recordings, but it takes 70 years for the signals to arrive. Almost everyone in those recordings would be dead by the time we see it, and the rest would be very old. We know this, without seeing them die, because we know how far away they are and we know what a human lifespan looks like.
The shiny from today hasn’t reached us, but shiny from the long long ago has reached us. We can see the general direction the pillars are moving with the shiny from the long long ago. Then we make a good guess.
Excuse me for a stupid question. Astronomy is not my specialty, and I lack understanding of physics of light traveling a long distance. How long the actual destruction of The Pillars of Creation took time? I mean, if we were standing right beside and watching it. I understand that whatever event occurred in a great distance from us, it takes some time for us to witness it visually, as the light (photons) travels from the source of event to reach our receptors. But if the explosion happened in a far distance, wouldn’t the duration of that explosion be the same, just late time-wise.
Because we know what it is scientifically and we know what will happen to it. If I hold a pen in the air and let it go, you know it will fall onto the ground. Same idea
Firstly, a couple of corrections – the Pillars of Creation are 7,000 light years away, not 400-500 million. And a light year is the distance that light travels in a year, so it is a measurement of distance, not time. So light from the Pillars takes 7,000 years (not light years) to reach us, so when we look at them we see them as they were 7,000 years ago.
So the simple answer to your question is that we don’t know for sure, and we won’t know until the light reaches us. It is only a theory, based on an image taken of a nearby dust cloud that looks like it could be the result of a shockwave from a supernova. If there has been a supernova it could have blown the pillars away as they are just dust and gas floating in space. If this happened, it happened 6,000 years ago, so we will actually see it happen in 1,000 years time.
We don’t know it. It’s partly why the commonly repeated phrase “…the light from this thing has travelled millions of years to reach us” is problematic. There is no cosmic clock. All information travels at the speed of light. So for all intents and purposes, the pillars of creation are still there until we don’t see them anymore. In fact their gravitational effect on us is also just now reaching us.
Another example. If the sun disappeared “right now” we would continue to orbit it. And see it, and sunbathe in it. 8 minutes later the lights would go out. But what does it mean to say that happened in the past? what past? It happens IMO when the light and gravity change reaches you.
of course if someone discovers FTL travel then i’m wrong.
If we could see that, then aren’t we seeing into the future? I always thought of the speed of light as being more akin to the speed of causality
It’s a bit pop-science to say things like this.
The speed of light is what it is because that’s how fast causality itself can propagate information across the unbroken fabric of space.
So it’s cause and effect that moves at the speed of light, and light just happens to be the only thing that can ride that limit.
We can make predictions of course, but how we’re seeing the Pillars now is how they “really are” to us in any meaningful sense.
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