That was interesting but I’m not sure it answered the question? Was the answer that they don’t “time freeze” at the threshold of event horizons touching each other, but instead “pucker out” to meet each other?
I agree the wording in the article isn’t too clear, maybe a bit oversimplified.
One thing to keep in mind. What we see as the black hole is really the “event horizon”. To a local observer there’s nothing special at that location. You wouldn’t notice anything crossing it.
So really as the black holes merge, we see their event horizons merge. It’s not really valid to say one horizon falls into the other, as they are simply space time points like any other.
What happens to the singularities is probably a whole lot more complex and I don’t know if it’s well defined. In addition, there’s a lot more typically going on around most black holes since many have accretion disks of materials accelerated at relativistic speeds and are also rotating causing other gravitational complexities.
Where I think the article hits the nail on the head, is we need complex simulations and ultimately more data on observations to create more accurate models.
What I just realised - imagine we are living in the future and have colonized distant planets. We might need a new tense that indicates that an event has already happened on that distant planet, but due to speed of light limitations, this information has not yet arrived at the observer.
The relevancy is obvious. Someone wondered if we will need new words for different nuances of tense, and this comment described that Turkish has some of those already.
Is this not some kind of sneaky simultaneity? You're imagining some absolute "this has happened" where, in your perspective, it hasn't yet.
I'm interested if anyone qualified could fix this issue for me. When we look into the distance, we see things that we describe as "happening X years ago" based on their light-year distance to us. We imagine that in the actual present at that location, what we're seeing happened X years ago. Is this not implying some absolute time reference that shouldn't really exist?
That concept is indeed meaningless in special relativity. So much so that mathematically there is no way to write down an absolute point in time, you can only write down time relative to another point in space time. Ergo saying something like 'that place at [same time as my absolute time]' is not even possible.
It could be possible to go faster than light and preserve causality. The problem is we don't know a way to do this -- all explored ways create contradictions based on the physical laws as we know them.
If you can imagine teleporting and still having a consistent timeline, then you can imagine going faster than light.
You can certainly imagine going faster than light, but that doesn't mean it's possible. Saying it could be possible is basically saying "our understanding of physics could be wrong". Technically correct, but at that point we aren't having a productive discussion. "Assume everything we understand is wrong -> we can now teleport"
Does it even have to be teleporting to break causality, to be honest? Given a long enough journey, wouldn't the Alcoubiere (sp?) drive accomplish the same thing? By making a warp bubble and folding space using gravitational forces, none of the laws of physics are broken and the user can still move faster than the speed of light (though it isn't possible due to the lack of anti gravity, which might not exist - so there's that).
It doesn't have to be teleporting. Any superluminal travel can break causality. As I linked elsewhere, Sean Carroll has a solo podcast episode[0] where he talks about a few methods by which time travel could be imagined to be possible, given our understanding of the limitations. As is the case with the drive you mentioned, it's often the case that it's something like "well, if we imagine some special case that we don't think is forbidden, we can do xyz". I imagine at some point a few of these not-technically-forbidden holes will be blocked, but also it's not a certainty that all that is true can be shown to be so.
Your link really doesn't provide any basis for FTL travel.
No, I know it doesn't provide any basis for FTL travel. It was more a link for the commentors stating that nothing can travel faster than light. I should have labeled it better =/
Well, it doesn't really show something travelling faster than light, any more than if you shot a laser at the moon and looked at the speed of the dot on the surface as you moved it through some angle. The dot can move arbitrarily fast, but nothing in the system is actually moving faster than light.
What is impossible for reasons related to space and time and light is going faster than light in the typical ways. It does not mean going faster than light is universally impossible, just those ways.
We are pretty sure FTL or “stargate” style teleporting would break causality. If anything like this is possible it means the universe is far, far stranger than we have imagined.
My understanding is that maximum speed is defined when going through space so light speed is maximum speed while going through space.
But I think theoretically we can defined travel through spacetime (or by transforming space itself) or something similar where a distance can seem to be travelled at higher speed than light is measured as space. I am thinking about this as I heard that when thinking that our Universe expands so each two galaxies lets say depart from each other will eventually speed up “faster than light” in the sense that the space itself expands.
Wormholes aren't true FTL travel, they change the geometry of space such that there's a new shortest path for light to travel from A to B. Setting up a wormhole between two points requires slower than light travel to extend the wormhole ends. But after initial setup it would still be amazing :-)
If you're interested in some simplified-but-still-roughly-rigorous discussion about the physics of time travel/causality, Sean Carroll did a solo episode of his podcast where he talked about a few different ideas in this space.
“Going faster than light” is impossible. The intuitive concept of velocity as something that can be infinitely scaled isn’t how real relativistic velocity works.
“Teleporting” and “having a consistent timeline” are oxymorons.
Was just going to say that we should perhaps start with using the term “speed of time” instead of “speed of light” to get in the right frame of mind.
But then I started to think about it and it doesn’t seem exactly right either. Causality kind of implies interaction, and interaction implies mass (no?), so causality as such must necessarily be strictly slower than C. That is, the speed of the propagation of the wave function between causally connects to events is C but causality as such are the interesting things happening at those events.
Not necessarily. Photons, for example, are massless. But you're still pretty much correct. Information cannot travel faster than C.
Though there may be some special cases that I'm not too familiar with. One I'm a little curious about is entangled quantum particles, though I'd have to do a little reading to be able to say anything further.
You might know that something will happen, but it hasn't happened yet in your reference frame. I guess this is actually just the return of the past, where you wouldn't know something had happened yet if it were thousands of miles away. I wonder if there's remnants of that time in the language used.
Well, if you observe two black holes moving towards each other, you might conclude that they "will" collide, But at the time when you made this observation these black holes have already collided, you just have not observed that. It's like using future tense. "I will go to work tomorrow", event though you don't know for sure if you will go to work tomorrow.
We might, but Relatively makes it counterintuitive.
In the past/future you find all the stuff within the corresponding light cone. The stuff outside the cones can flip between being what seems (non-Relativistically) like it should be past and future, can be either depending on your motion relative to it, so an extra tense for spacelike separation is something I can imagine a sufficiently advanced civilisation using.
But NASA already has that situation with their Mars rovers already. When ever those do something, its always 5-20 minutes when you know it has already happened but the signal is not on earth yet.
It is not just the future that needs it. Time travel stories are part of our mainstream fiction and so we need to deal with time travel tenses when discussing the plots of those stories.
We have this in my native language; adapted to English, it would sound like <It will have happened>. Three black holes will have merged in a nearby galaxy.
Maybe we could borrow from our distant (or not so distant) ancestors, where an event might have happened on the other side of this planet, but due to the speed limitations of ships sailing the ocean, this information had not yet arrived at the observer.
These are still tens if not hundreds of thousands of light-years apart.
It will take how long, a billion years?, for dynamical friction to bring them together?
How close do they need to be before gravitational radiation begins to carry away enough energy that merging can proceed without depending on external mass?
The article mentions the "final parsec problem," which implies that a binary pair will never merge. A three-body arrangement is one scenario where a merger can take place.
"Gravitational waves can cause significant loss of orbital energy, but not until the separation shrinks to a much smaller value, roughly 0.01–0.001 parsec."
Thank you. This seems to suggest that the black-hole mergers picked up by LIGO must have involved an unseen third participant. Or is this required only for supermassive black holes to merge?
Is there any rational hope of picking up (e.g.) periodically varying red-shift of secondary radiation from the (presumably large) collection of black-hole pairs stuck in parsec-range orbits? Is there any process tending to align the rotational axes of accretion discs on bodies in this condition?
Of course they are! It's just that this mass concentration appears to be outside a domestic regulated market and NASA/ESA are as helpless as the FTC against laws of nature.
It’s slightly weird to think this will happen at a certain time for us but presumably at this point space time will be bent in such a way that what does time even mean anymore…
Anything within 1 billion light years from us is considered “near by universe”, it’s sometimes also called our local universe.
Tt’s the region of space around us in which cosmic evolution doesn’t play a major factor for observations unlike something that say is 10 billion light years away.
Basically it’s a anything close enough to us that when we observe it we can assume that at least as far as the galactic evolution goes it’s in a current or “developed” state, as in mature and fully formed galaxies.
That's usually called "space", not "universe". The universe is the entirety of space around us. By virtue of countability, the phrase "nearby universe" is problematic since it suggests contrast with other, "far" universes (which don't include the space around us).
Space or outer space isn’t a term commonly used in cosmology which is the field of study of the chronology and evolution of the universe.
And in this context it makes perfect sense within 1b light years we can observe the universe as it is more or less in its current state, so looking at something 100 light years away or 1b isn’t that different. Once you go past that line you begin to go further and further in time so different stages within the evolution of the universe take precedence over local phenomena.
It doesn’t indicate that there are other universes out there just due to the speed of light what we can observe can be drastically different than what is around us as well as what is actually going anywhere else at the current age of the universe.
You do realize at the very least that different academic fields have developed different lingo, and that words therefore mean different things in different settings?
Can you read the definition? “Local Universe - Studies of the nearby universe encompass a region of approximately 1 billion light years in radius, over which the effects of cosmic evolution are small.”
While it does sound weird, it is a term that scientists are using to distinguish between the universe as a whole of existence that was, is including us and will be, and what we can observe within our capabilities from our position on Earth, in the Sol system, travelling in the Orion Arm of Milky Way galaxy. The universe and the observable universe.
This of course has nothing to do with the popular scifi concept of parallel universes.
The observable universe isn’t the same as the local universe. The observable universe encompasses a region of approximately 13.7B light years from our point of observation which is earth, the local or near by universe is limited to about 1b light years.
Both have their usefulness when conducting observations as we need to take certain assumptions based on what we know.
The former is anything that is currently within our cosmological horizon the latter is anything we can observe that is in the same relative slice of time or cosmological development stage as us.
A better call would have been "nearby part of the universe", with "the" being the most important word that should not have been left out. It may not have been as terse/catchy as "nearby universe", but it would not have strayed into controversy (the kind of which we see here).
You missed a key word. I'm not against the use of the phrase "nearby area" which is obviously acceptable, just like "nearby" + any_noun is acceptable. Anyway, there are also plenty of cases - although they rarely occur - where the phrase "your nearby area" could be used. This just isn't one of them.
Hot singles in your nearby area doesn't make sense, because it is unclear what the intention of the word "nearby" is. It clearly modifies "area". So the area is nearby something. By what is it nearby?
This analogy fails because distance on a cosmological scale means both space and time whilst on smaller scales we measure space and time as two distinct parameters.
If we go with the single analogy it would be like filtering on Tinder based on distance as well as when the last time that account was active.
It’s like if going more than 50 miles further out of your existing location would only show tinder accounts from 5 years ago which wouldn’t be relevant for what you are looking for which are people who are single right now and looking right now.
> "Hot singles in your area" is a bit different than "Hot singles in your nearby area."
I wasn't using the word "area", though.
> The term "nearby universe" is perfectly fine, as far as the English language goes.
Not according to my language sensibility at the very least. Just like sibling comment's remark about "nearby house" when talking about the very house you're currently in.
One is class¹ inheritance, the other one is (most likely about) wealth inheritance. They do, however, both respect the notion of inheritance, I don't see why anyone's sensibilities would be affected. But then comes "local universe", which although refers to the local part of THE universe, it drops the definitive article, only because coining a new (albeit controversial) term in astronomy is more rewarding for someone looking to leave a mark on the domain than to respect logic to a more sensible result.
¹ Let's leave for now what "class" means for programmers vs. other kinds of people.
In this case you literally gave a better example “class”, that said in cosmology there is only one universe ours.
The multiverse and other theories of multiple universes nominally belong to other fields of study.
Cosmology is the study of the universe we live in, specifically it’s development.
That’s why we have terms such as the local/near by universe and the observable universe. I find odd that none that that seem to take offense with the former mentions the latter, since grammatically they are identical.
No, "another universe" is a contradiction since if we found one, our universe would simply be bigger than previously thought and cosmological physics would need an overhaul.
Max Tegmark covers this in Our Mathematical Universe.
It's a question of definitions. He makes the argument that defining "universe" to mean "our visible universe", that is, a radius of around 14B ly, is the most useful; if you assume infinite space and infinite matter (which seem to follow from the theory of inflation, which has provided explanations and predictions elsewhere), there are likely infinitely many universes all around following this definition (for other visibility scopes).
Just an unnecessarily pendantic note: the visible (observable) universe would be defined as anything that emitted radiation that would have reached us, and in an expanding universe that means it's considerably larger than 14-ish billion light years radius. Conveniently, it works out to about 14 billion parsecs, so nobody needs to remember another number, they just need to do the conversion.
Wouldn’t it be fair to consider a causally disconnected (relative to us) place to be another universe, at least in layman terms? After all, it is expected in a couple trillion years that nothing outside the local group will be observable.
Who knows how much “disconnected universe” there is. Unless that is somehow known, which seems difficult since it is by definition causally disconnected.
Max Tegmark covers this in Our Mathematical Universe.
It's a question of definitions. He makes the argument that defining "universe" to mean "our visible universe", that is, a radius of around 140B ly, is the most useful; if you assume infinite space and infinite matter (which seem to follow from the theory of inflation, which has provided explanations and predictions elsewhere), there are likely infinitely many universes all around following this definition (for other visibility scopes).
This was certainly true when I was a kid, and "universe" meant "all existing matter and space (observable or not)".
As a youtube-couch expert on astrophysics, I hear "universe" redefined as something like "a bubble of matter and spacetime that is 'quarantined' and can never communicate with the rest of the cosmos" whenever multiverse theory is discussed.
I know this has nothing to do with the article but there’s been too many global warming news headlines recently and it’s making me depressed. I read this one and imagined the opening to be…
> The effects of global warming have produced wildfires, hurricanes, drought, and other extreme events at an alarming pace. The situation has gone from bad to worse as scientists recently discovered three super massive black holes merging together in our nearby universe.
I think it’s important we all become aware of the reality of the climate crisis. The fact that we aren’t yet is one of the reasons we have failed to deal with it better.
I was very surprised to find out that some people around me, which are software engineers and reasonably well informed people, were oblivious to the dangers the climate crisis poses.
To this end, maybe it’s important to repeat it many times, until it hits everyone.
http://curious.astro.cornell.edu/about-us/91-the-universe/bl...