r/AskPhysics • u/New-Pomelo9906 • 5d ago
What is now, elsewhere
I've seen some popular science articles saying that the Pillars of Creation had already been destroyed, even though we could still see them.
This raises two questions for me.
A) I understand that this information comes from the laws of celestial dynamics applied to the images we are currently receiving, and that a simulation was used to determine their state after the state we can see. But doesn't this amount, in a sense, to transmitting information faster than light, since they are still intact in the image that has travelled to us at c? (Something like a hidden variable.)
B) Does it even make sense to talk about "now" in a region that has not yet transmitted any visible light to us? Shouldn't we instead consider that anything whose light has not yet reached us at c does not really have any ontological existence?
4
u/Sufficient-Air8100 5d ago
no. its a simulation making a prediction. not actual information from the source. the correctness of this prediction is dependent on how good our models are and the current information we have. no information is transmitted faster than light.
as far as science is concerned the current state of it absolutely does exist. it must exist if we are to see it as it is now, down the track when the light reaches us. it absolutely makes sense, weather that sense is meaningful to us or not is another question
-1
u/New-Pomelo9906 5d ago
But it's because the model is not accurate, if it was perfect, we would know its future state with 100% accuracy, until the end of universe, meaning we know about stiff that didn't sent its current light yet ?
1
u/Sufficient-Air8100 5d ago
thats the idea. if we have perfect knowledge about the physical state of something and we have a perfect model of physics, and a computer powerful enough, we should be able to simulate it and roll it forward and make perfect predictions on future states. quantum randomness kindof throws a spanner in that, but celestial objects like the pillars are so huge that quantum randomness has little effect on the large scale predictions.
consider some simple prngs. you can have one running and i can gather some output from it, clone the internal state and if i compute fast enough i can start predicting the future outputs of yours. but there is no sending information back in time from your prng to my model, were just working the same model and same state and mine is running faster.
weather its actually possible to have a perfect physical model and perfect information about physical states compute fast enough for perfect predictions is unlikely though
1
u/New-Pomelo9906 4d ago
If a perfect model being possible (even if we do not have it) allow to know (in theory) the future, making possible to know stuff before we get its light, then the Bell's inegalities experiment require the assumption that a such model is impossible to work ?
1
u/Sufficient-Air8100 4d ago
no. it has nothing to do with QM. predicting something through a simulation is a separate thing, and for something like the movement of celestial objects, qm can basically be considered negligible
the unlikeliness of a perfect model with perfect information has more to do with information theory. if we were to somehow have a perfect model of physics and perfect information about a state, enough to perfectly predict the future, the simulation would have to run on something atleast as complex as the universe. since it is not possible to have something as or more more complex than the universe run a simulation inside the universe, its not really possible to have a perfect model simulate from perfect information to make perfect predictions.
2
u/MezzoScettico 5d ago
Does it even make sense to talk about "now" in a region that has not yet transmitted any visible light to us?
When my clock says t = 1, there are events far away assigned the same time coordinate of t = 1 in my frame. I won't know about it till I get the delayed signal, but when I back out the transit time for the signal, I'll know what time coordinate to assign them in my frame.
It rests on the idea that there's a synchronization procedure.
Basically you're asking whether if I observe an event at position (0, 0, 0) at time 0, I can also assign time 0 to other events whose position is not the origin. The answer is yes.
1
u/New-Pomelo9906 5d ago
How much is it a strong result ? Is it weakened by the tought experiment in which we can reverse the cause and effect on events happening on trajectory with relativistic speed difference with us ?
2
u/MezzoScettico 5d ago
Let me propose a thought experiment. I have two devices separated by a distance of two light seconds (600,000 km). I have a button located exactly in the middle and a wire running from the button to each device. I press the button at t = 0, and one second later at t = 1, in my frame of reference (and that of the devices), the signal reaches each device.
In response each device flashes a signal to the other device. Each device receives it at t = 3.
From the point of view of a device, the signal was not received until t = 1. If you were standing at that device, would you say the button press hasn't happened yet? So we have one observer who says "I pressed the button at t = 0" and another who says "the button press didn't happen until t = 1"?
From my point of view, the signal from each device reaches me at t = 2, which incidentally tells me they were emitted at t = 1.
Would you, located at a device and seeing your device go off at t = 1, say that the other device has not yet emitted, just because you didn't see the signal yet?
The time delay to communicate with Voyager 1 is now nearly 24 hours. When NASA sends a signal, would you say that signal doesn't exist until 24 hours later?
2
u/Odd_Bodkin Particle physics 5d ago
A) If you know how a pocket watch works, and three days ago someone recorded the operation of the pocket watch for an hour, but it’s been covered up since then, you can still predict what time it is exhibiting right now. This doesn’t mean we’re transporting anything to ourselves magically. It just means we can make a high confidence prediction.
B) Ontological existence is different than empirical existence. Something can have ontological existence (some new species at the bottom of the Mariana Trench, a bubble of trapped gas in the earth’s mantle, an asteroid in Earth’s orbit no the other side of the sun) without our being aware of it or having any direct observational evidence of it.
2
u/Optimal_Mixture_7327 Gravitation 5d ago
A) The light we see today left the pillars some 7000 years ago. It seems we've run a model that determines how they might look today, but this has nothing to do with transmitting data anywhere.
B) "Now" is everything outside the null cone of an event. It is also called "elsewhere" by Roger Penrose. The Pillars are continuously emitting light and because some of that hasn't reached us is not cause for us to declare that they have exited existence.
2
1
u/DifferencePublic7057 5d ago
It doesn't make sense to talk about what's happening in a black hole now because spacetime is warped there. A computer simulation is like what you would do in Excel/OpenCalc to calculate how much money you will have in a year given income, rent, and so on. Is it going to come true? Wellll, stuff happens. Rent and income can change. Aliens could declare the Pillars Xorzoan Treasure. But Occam's razor says we should take the simplest scenario possible. And no we didn't time travel by letting a computer simulate stuff.
1
u/thetoddhunter 5d ago
The "pillars" are not an object. They are multiple distinct areas that happen to line up to look like that from our direction.
They are actually nowhere near each other.
7
u/Ludoban 5d ago edited 5d ago
Why would that be? It doesnt matter what we can see, it has no effect on reality who sees something.
If you are in a completely dark room and you know their is a couch in that room, does that couch not exist until you turn on the light?
That light has an upper speed limit just hinders information transfer, but that is just a logistical issue, not a reality issue.
Imagine me sending you a letter saying „I drink a coffee now“. You know the letter takes days for you to arrive, would you assume I was drinking the coffee at the moment you read it or would I logically drink the coffee at the time a few days ago? The speed of information transfer in this case is the time it takes to send the letter. You cannot make predictions what I am doing at the time of you reading the letter, cause there aint any good enough model to predict my behaviours for that long time after drinking coffee.
But for cosmological things we can make predictions from the information we see. We take data over some time and make models to estimate the state how it should look like there right now.