Coming black hole collision -- help me to understand this NYT article

This article talks about a “coming” black hole collision that is expected to happen in 100,000 years. The black holes are in a galaxy 3.5 billion light years away. Is the “coming” black hole collision something that (if it happened) already happened over 3 billion years ago? Or, did they already take the distance into account when they say it will happen 100,000 years from now? Or am I missing the point entirely?

Sorry if this is obvious; I’m not a science person.

Humans will probably be extinct 100,000 years from now, anyway, so I wouldn’t worry about it.

LOL, I’m not worried about it; I’m just trying to figure out what the article is saying.

It happened back when the earth was new, assuming the earth is 4.5+ billion years. I think the easiest way to think about this is a light year is a year; it’s just the distance light travels in a year so it’s both distance and the length of time of a year. So there’s no way for anything 3.5 billion light years away to be seen here except after 3.5 billion actual years, which means it happened a very long time ago (at least before I was born!) and a very long distance from here.

“Is the “coming” black hole collision something that (if it happened) already happened over 3 billion years ago?”
"Or, did they already take the distance into account when they say it will happen 100,000 years from now? "

So we have a difference of opinion between @lergnom and @menloparkmom!

(Lergnom – I understand that the light hitting the earth from that location is 3.5 billion years old; I just didn’t understand what the article meant by the “future” in this context).

I agree with Lergnom.

It would appear that this collision already occurred some time ago, but the astronomers are watching the pre-event display right now. They are also excited about detecting the gravity waves from the eventual collision, but since that is 100,000 years in our future, they are trying to look for similar encounters that might be more timely.

It takes 8 minutes for the light from the sun to reach us. When you look at the sun, you are seeing what the sun looked like 8 minutes ago.

“As you look outward into space, you’re actually looking backwards in time.”

Right; that’s the premise of the question. But the article seems at least a little ambiguous in referring to an “upcoming” event. Upcoming from whose perspective?

“Coming Black Hole Collision”?

Oh Gawd, Mary! We’re all gonna die!!!

The event we would see if we live long enough, etc. is 100k years in earth’s future but 3.5 billion - 100k years in the past. So assuming 3.5 billion is exact, which isn’t true, it would be light emitted 3.4 billion years ago. So it’s upcoming from our perspective but happened so long ago words can’t describe.

Note that astronomers recently identified a galaxy, “EGS8p7”, which is about 13.2 billion-years-old. That’s only an estimated 600 million years (only!!) after the creation of this universe. This is interesting but hard to understand because I think it was written by someone who had no idea what the scientists were saying:

"The Big Bang is the theory that posits that the universe continuously expands so out of its original dense, hot state, which was characterized by high amounts of free-roaming electrons, protons and photons. After a cooling period, protons and electrons began to mix together to form hydrogen atoms that allowed light to travel through space. This allowed for galaxies, like our own, to begin to form, as gravity could then begin pulling matter together. In most known galaxies, the clouds of hydrogen atoms absorbed radiation emitted from newly-formed galaxies, a process known as reionization, but as the researchers show, for EGS8p7, this was not the case.

“If you look at galaxies in the early universe, there is a lot of neutral hydrogen that is not transparent to this emission,” [Adi] Zitrin said in a statement. “We expect that most of the radiation from this galaxy would be absorbed by the hydrogen in the intervening space. Yet still we see Lyman-alpha from this galaxy.” Lyman-alpha is an emission line of hydrogen through space, which, as stated above, usually indicates the formation of new galaxies or stars as the clouds of hydrogen absorb radiation. It is believed that Lyman-alpha emissions should have ended after the reionization process billions of years ago, but now the detection of Lyman-alpha lines may turn accepted astrophysical theories on their heads.

“The surprising aspect about the present discovery is that we detected this Lyman alpha line in an apparently faint galaxy…corresponding to a time when the universe should be full of absorbing hydrogen clouds,” [Richard] Ellis stated. One possible explanation for this previously unobserved phenomenon is that the absorption of radiation by the hydrogen clouds did not occur in a uniform manner across all galaxies. In addition, it is possible that EGS8p7 is populated by unusually hot stars and that the hydrogen clouds were created, or reionized, much earlier than was previously thought.

The novelty of the finding also has to do with the distance of the EGS8p7 galaxy from our own. Using spectrometer data the team gathered from NASA’s Hubble Space Telescope and the Spitzer Space Telescope, they were able to discover the galaxy’s redshift, or the red light that extends from the galaxy that indicated its distance, similar to the way some sounds cause the Doppler effect. In the case of EGS8p7, its redshift reading is 8.68, while prior to the discovery, the most distant galaxy we were aware of had a redshift of 7.73.

“We are currently calculating more thoroughly the exact chances of finding this galaxy and seeing this emission from it, and to understand whether we need to revise the timeline of the reionization, which is one of the major key questions to answer in our understanding of the evolution of the universe,” Zitrin says.

Me again if you made it this far. Astrophysics is not my strong point but two points leap out: huge redshift and hydrogen emission (which occurs when the atom’s electron drops in its orbital and this drop releases energy we can detect) where there should be none. BTW, I have no idea if this finding will stand up. I’m putting it here to show how far back in time we can see.

If you want weird stuff, look up the strange discussions about what happens when the sun explodes. If it explodes in a non-uniform matter, what would happen to the earth (presuming we’re not in the immediate blast)? That is, what happens to gravity when the sun suddenly loses all that gravitational pull and thus what imaginatively would happen to the planet if it “survives” and suddenly the relationship of earth to sun is blotto. Of course if the sun explodes uniformly then the question is what happens to the earth before the radiation eliminates us from existence (so quickly we would be unaware of it happening, like an infinite number of atomic bombs going off on top of you). This involves questions of how gravity is “transmitted” because if you think of the drawings of general relativity space - with the big deep well for a black hole, etc. - then if gravity at the sun changes then do we experience that without the speed of light lag? Since general relativity is local, the usual thought is we never find out because the change arrives with the radiation and if the sun explodes in a different direction then we’d feel the effects as the change in the gravitational field arrives in about 8 minutes 20 seconds. In Newtonian physics - this is the oddity - the effect is usually deemed instantaneous. But of course life follows Newtonian rules except when it doesn’t.

This is a fine response - I’m sure it answers the original question that the OP had in mind. Unfortunately, it’s not quite 100% right. Here’s a more complete answer, but it might confuse more than enlighten -

[] Earthlings will observe the light and gravity waves from the collision approximately 100,000 years from now.
] Someone using the Earth calendar would say the collision “would happen” at time = 3.5 Billion years B.C., and at a distance of 3.5 Billion light years from Earth.
* However, this does not mean the collision occurred “a very long time ago” or that it occurred 3.5 Billion years ago. Because light from the collision could not have reached us yet, it’s impossible to 100% say that the collision occurred in our past or in our future. Neither is necessarily true. Some hypothetical aliens might think the collision occurred at an earlier time than Earth’s “now”, while others who are moving very fast relative to us might think the collision will occur at a later time than Earth’s “now”
[li] For example, if we had some Star Trek ray-beam that prevented black hole collisions and traveled at the same speed as light does, we could fire it now and stop the collision from occurring. This would obviously be impossible if the collision actually occurred in our past (unless you also had a Star Trek time-machine too :slight_smile: But that’s impossible.).[/li][/ol]

I put the “would happen” in the 2nd bullet in quotes because the verb actually needs to be in some weird conditional “past but possibly present or future” English tense that I don’t know. As was said on a related subject by Douglas Adams -

The event happened from earth’s perspective 3.4 billion years ago - taking the numbers as given - but I would agree that if you were somehow able to violate the essential realities of movement and proceed at light speed or near it then this changes. (I’ve yet to see an example of this happening.) Hypothetical aliens on some other planet - or in some other universe - have a different perspective and of course that could make the event occur in their past because that is the same as moving earth and this event closer together in space and thus time. That’s just saying that other people see things differently. Like if there’s an earthquake and a tsunami, you feel it first here and then over there, but you don’t say “it happened in a different reality” or anything like that, just that you are in different locations.

As a note, one thing that people often forget about “aliens” is if we find some evidence - say a radiation pulse that spells out “hey dude!” - that would be coming from the past. Even if somehow the planet near Alpha Centauri, which is the closest star to ours, near-magically bore communicating intelligent life, we’d be “seeing” what happened over 4 years ago. It’s the same thing as the time lag in transmissions to and from the space station (not big, less than a second) and about 1.25 seconds one way to the moon (and thus 2.5 back and forth) and as long as 21 minutes one way to Mars (when we’re furthest apart). It takes hours to talk to Pluto. This is the exact same thing as the black holes colliding 3.5 billion light years away.

Given the age of the universe and the length of time it has taken for humans to evolve - not long - when people talk about the existence of life, they tend to focus on the “right now” aspect, as in there are x many stars and we can extrapolate y many planets and that generates an idea about potential intelligent life which is pretty darned large but that tends to ignore the relatively small window of human existence and thus the potentially small window of other intelligent life. In other words, if we take roughly half the existence of the universe - roughly 7 billion years (much more than the existence of the earth) - then maybe intelligent life has existed in small swatches many, many times. We started wearing clothes maybe 170,000 years ago and that’s a pretty small number compared to 1 billion, let alone 7 billion. Say human life exists for 10 million years or so. Still not very long. So it may be necessary to spread the possibility of intelligent life over time as well as spatial counting of potential places and that says to me the odds of finding intelligent life are lower than often estimated (by people who want to find intelligent life).

That’s the way I think about it, too, @Lergnom, but I’m no cosmologist. But your articulation of the issue is exactly why I found the New York Times’ language so imprecise and ambiguous. Maybe this is more of a grammar question regarding popular science reporting.

Not exactly, and that’s what makes this stuff weird.

In the example of the earthquake and a tsunami that hits (say) Japan, the earthquake causes the tsunami. The earthquake therefore certainly occurs in the past relative to the tsunami. No observers, whether they’re on earth or moving near light speed, can disagree about this - otherwise cause and effect would be violated. Thus, all observers would say both a) the earthquake occurs at an earlier time than the tsunami and b) the earthquake occurs in the tsunami’s past.

But there’s a difference between saying that event A occurs at an earlier time than event B and saying that event A occurs in event B’s past. In normal, everyday life this difference is undetectable so we don’t distinguish between the two. But when you’re talking about distant galaxies the difference can be large.

If event A occurs in event B’s past then every observer will agree that event A occurs at an earlier time than event B. But if one observer says that event A occurs at an earlier time than event B then it may or may not be true that event A occurs in event B’s past … and other observers might disagree about whether event A occurs at an earlier time than event B.

Saying that event A occurs at an earlier time than event B is irrelevant and meaningless since different observers can disagree about this. Saying that event A occurs in event B’s past is meaningful.

Getting back to the collision – humans on earth would say the collision occurs at a much earlier time than the “now” on earth; 3.5 Billion years earlier. But the collision does not occur in our past. And other observers with equal validity would say the collision occurs at a later time than the “now” on earth.

Of course, I’m sure the OP just wanted to know what humans on earth would observe, but the question of whether the event “already happened” opens up a big can of worms. And the event did not “already happen” in any meaningful sense (unless you use cosmic time, but that’s another huge digression).

It’s a little confusing, but don’t blame me; blame God and Einstein.

How could this be? This collision occurs/occurred 3.5 billion light years away. In 100,000 years, the light will get to us and we will detect this collision. If we fire your ray-beam now, in the next 100,000 years, it will not go 3.5 billion light years, but only 100,000 light years. How is it going to get to the collision 3.5 billion light years away in time in order to prevent it the collision? Wouldn’t the light ray have to go infinitely fast, or at least faster than light?

Cardinal Fang - You are right to object. I wrote something quickly to make a point, but I was sloppy since I didn’t define “we” and “now”. I should have realized someone would call me on it. Here’s a more careful version, but it’s a little harder to see the point amidst all the words -

(For the purposes of this story, please ignore the fact that Captain Kirk is supposed to be a one of our collective descendents).

Let’s say the Enterprise is dispatched to the colliding galaxies to stop the collision. Mr. Spock invents a ray-beam that prevents black-hole collisions, and the beam travels at the same speed as light. They get to within 10,000 light years of the cores of colliding galaxies and are closing range at very high speed (but slower than light). About 10,000 years (measured by the Enterprise’s clock) before the collision occurs, Captain Kirk fires the beam. It takes 10,000 years for the beam to hit the target, but when it does it stops the collision with 1 second to spare (Hurray, all the inhabitants are saved !!).

Theoretically, this could happen. This would not contradict any evidence that we on Earth have already gathered, though in 100,000 years our astronomers will be in for one big surprise as they’re looking through their telescopes.

In his log, Kirk notes the time that the beam was fired, using the Enterprise’s time clock. Later, the Enterprise discovers that @al2simon was wasting time on the internet typing this post. They also find out that I was typing this post exactly 900 years before the beam was fired (measured by the Enterprise’s time clock). The important bit is that the 900 year figure doesn’t violate the laws of physics and could theoretically be true (this is the part someone has to take my word for).

Thus, Kirk was able to stop the collision by firing the beam at a time 900 years later than the time he says Sept. 18, 2015 on earth occurs. Since this is possible, there’s no way the collision occurs in my past. There’s also no way the collision could have “already happened” from our perspective here on Earth.

OP here – No, I wasn’t asking what people on Earth would observe; I thought the language in the NY Times article was ambiguous and I was asking for clarification of that ambiguity. In common parlance, we talk about cosmological events happening in the past all the time: the Big Bang happened in the past, the Milky Way galaxy is xx numbers of years old. And we say that the light hitting the earth allows us to see events now that happened in the past. We understand that the photos of Pluto were taken at an identifiable time “a” and arrived on earth at some later time “b.” So, in the context of those LANGUAGE CONVENTIONS, it is confusing and ambiguous for the NY Times to talk about the collisions of these particular black holes as something that is expected to happen in the future, given the language conventions that are used in describing other cosmological events in popular media.

Here’s a cosmologically naive question: By virtue of the fact that the collision, if it occurred, happened 3.4999 billion years ago when measured from the location of the collision, can’t we, as a logical matter, RULE OUT certain effects from the collision? For example, can’t we say, with certainty ;-), that the collision didn’t cause immediate rapid inflation of the universe similar to what happened after the Big Bang, because if it had, the effect would have already been felt on Earth? (I’m not saying that it could have caused such an effect; I’m just saying that there’s SOMETHING about its having occurred in the “past” that logically allows us to narrow theoretical possibilities).

And, I’m not totally buying the explanation that the words “past” and “future” are meaningless to cosmologists. At least as reported in popular media, cosmologists talk all the time about analyzing currently observable data to make inferences about long-past events – take the analysis of cosmic microwave radiation as telling us about the beginnings or “history” of the universe. So it is not the case that any concept of past or future is anathema to cosmologists.

Again, my focus in asking the original question was the NY Times use of language.