Any time "imminent" is used in astronomy, you have to remember 1 million years is imminient when speaking about the universe. So for them to say "within 3 years" that's like go get the popcorn, you don't want to miss it level warning!
In fact, 3 years is too lucky that I must predict this is a false alarm. https://www.science.org/content/article/crash-titans-imminen... reports "Fabian says the chance of such a merger taking place so close to Earth in any given year is one in 10,000" and evidences presented don't seem strong enough to overcome 1:10,000 prior.
Meh, some lucky bloke eventually wins the powerball too. In our lifetime. Multiple times in some cases, but definitely different winners sometimes weekly. The odds of winning the lottery are a lot higher than 1:10,000.
The universe is close to 14 Billion years old. 1:10,000 is like nothing to the universe. There are several orders of magnitude stars in the universe that you could have 1:10,000 events occur daily. You as a member of the very johnny come lately human species (in terms of the universe's age) might feel like 1:10,000 seems high.
I mean, I support scratching this particular lottery ticket, because unlike lottery whose reward (money) is fungible, if it pays off we will get information we won't get any other way. But we shouldn't expect to win, that's all I am saying.
You could say "it's already happened" as a first approximation but this isn't really true because the statement implicitly assumes there is some kind of universal "now" that can be used as a reference point for timing things.
No such universal "now" exists. That's why the question "What's happening right now on Mars?" makes no physical sense. "Now" is a function of both when and where you're standing.
The question "What's happening right now on the other side of my living room?" also doesn't make any physical sense. But the difference between reality and our perception of it is less easily detectable in that case.
Incorrect. Relativistic differences in simultaneity between observers have nothing to do with light travel time between them and everything to do with different velocities. The other side your living room, and even the other side of the galaxy, is moving close enough to the same speed that simultaneity is perfectly well defined between them. So we can confidently assign times in the past to events based on what we see in the present, in the knowledge that they will be consistent with times assigned by other observers in different locations at the same speed.
The only wrinkle in the scenario of a distant galaxy is cosmic expansion inducing a different reference frame by causing motion relative to Earth. However, if the redshift isn't more than a few percent then the time dilation won't be either, so we can be pretty sure it will be in the past by any definition that isn't moving a fair fraction of c relative to us.
Don't confuse light travel time with relative simultaneity. Relativity does weird things to time but that's not one of them.
I agree that a reference frame that has about the same velocity as the stuff you care about is in some sense privileged. But the fact that we haven't seen the merger happen yet means that it's outside our light cone, which means there exists a reference frame where the merger hasn't happened yet.
that is to say, t_{this_coversation} < t_{merger}, in that frame.
It is not too strong. GP specifically claimed that simultaneity depends on "where you're standing". This is wrong in all reference frames.
As for timing of distant events, GP didn't make any reference to other reference frames at arbitrary velocity, only different positions. In our reference frame, which they were implicitly talking about, the merger (assuming the prediction is correct) was in the past, unambiguously.
There is a universal now. Just because you are in a different location it doesn't change what now is. We have clocks all over the earth synced close to each other depsite being located in different places. While physically it may be impossible to perfectly sync clocks in theory we could have theoretically synced clocks.
I don't think this is true. General relativity says that time slows down under greater gravitational forces. This has been experimentally proven. Therefore clocks at different elevations run at different speeds.
Yes. In addition, Special relativity says clocks moving faster through space tick slower than clocks that move more slowly.
So let's say you're a GPS satellite. GR says your clock ticks too fast because you're farther from the center of the earth's gravity well than the wristwatches of people on the surface.
But SR says your clock ticks slower than a wristwatch on the surface because you're whizzing through space at ~15,000 km/hour.
Which is right? Both. And they do not exactly cancel each other out (in general). So both GR and SR have to be taken into account to make GPS satellites produce accurate locations and times.
You can refer to it differently, but time progresses at different rates at the different places. So in your example, physical processes (i.e rusting, aging) at place B happen 2X as fast as those at place A.
>but time progresses at different rates at the different places.
What's the problem? We can still have a now defined as I mentioned above. t1=t2=0 at the start. Now when t1=x for place A will refer to when t2=2*t1 at place B.
"the distances and even temporal ordering of pairs of events change when measured in different inertial frames of reference (this is the relativity of simultaneity); and the linear additivity of velocities no longer holds true."
>the distances and even temporal ordering of pairs of events change when measured in different inertial frames of reference (this is the relativity of simultaneity)
I'm not saying to use different frames of reference. I am saying to use a single universal frame of reference.
If you think about the amount of time it takes to get information from Mars to Earth, it would be similar but on a much bigger scale. It takes somewhere around 20 mins one way for Earth/Mars communications depending on oribital positions. By the time we received the confirmation that landers on Mars were safe, the lander has already had a cup of tea.
The lander wasn't in paused motion so that everything times out with us on Earth. Same concept with deep space objects. What we see is the information as it was when it left. To see what happened just now, we'll have to wait another few million years.
So information is relativistic I first thought, but independent causal actions are not. But that doesn’t explain that different frames can have different experiences of time.
I shouldn’t read too much about relativity before my morning coffee.
