While I understand what they mean...
-
In the end, it all boils down to your definition of "NOW". How do you define a NOW that's valid regarding to relativity and isn't restricted to a specific reference frame?
Now is Now. The Event was 28140 years ago, but the observation of the event was NOW. It is like watching a recording of a horse race. The race may have occured yesterday, but because you were observing it today, it is happening NOW to you, but in reality it is 24 hours old!
------------------------------------ "I want you to imagine I have a blaster in my hand" - Zaphod Beeblebrox. "You DO have a blaster in your hand" - Freighter Pilot "Yeah, so you don't have to tax your imagination too hard" - Zaphod Beeblebrox
-
Isn't it that the object is 28000 light years distant from our current position? From our perspective/frame of reference the light from the explosion first reached here about 140 years ago. What we see now is the object as it appears now from our reference point. I think the media try to put it as simplistically as possible for headline, audience numbers and sales purposes.
Ah you mean 'Physics for the Hard of Understanding'! :)
------------------------------------ "I want you to imagine I have a blaster in my hand" - Zaphod Beeblebrox. "You DO have a blaster in your hand" - Freighter Pilot "Yeah, so you don't have to tax your imagination too hard" - Zaphod Beeblebrox
-
It happens all the time. My particular bugbear is the use of lightyear as a measure of time or maybe the words Wattage and Ampage, it's a close call.
Parsecs and the Kessel Run! :)
------------------------------------ "I want you to imagine I have a blaster in my hand" - Zaphod Beeblebrox. "You DO have a blaster in your hand" - Freighter Pilot "Yeah, so you don't have to tax your imagination too hard" - Zaphod Beeblebrox
-
When writing "That's not allowed", I meant "That's not allowed in the relativity theory, as otherwise you would end up with contradictions". You're free to use another theory.
Thanks, I'll stick with CQM. :)
"The secret of happiness is freedom, and the secret of freedom, courage." Thucydides (B.C. 460-400)
-
Now is Now. The Event was 28140 years ago, but the observation of the event was NOW. It is like watching a recording of a horse race. The race may have occured yesterday, but because you were observing it today, it is happening NOW to you, but in reality it is 24 hours old!
------------------------------------ "I want you to imagine I have a blaster in my hand" - Zaphod Beeblebrox. "You DO have a blaster in your hand" - Freighter Pilot "Yeah, so you don't have to tax your imagination too hard" - Zaphod Beeblebrox
Dalek Dave wrote:
Now is Now.
Well, you are right with your idea of now; but I have a different idea of now, and I think it's also valid - it depends on how you think of the universe; for me, observation=event; I can live without absolute time. From http://www.badastronomy.com/bablog/2008/05/14/youngest-galactic-supernova-not-aliens-found/#comment-175177[^]:
Think of it this way: we literally cannot know what’s happening “now” at that distance; we have to wait 28,000 years to find out. In point of fact, there is no “now” at that distance, according to the equations of relativity. Now is simply now, and that means that what we see happening through our telescopes is happening now.
And another comment there:
1. Phil is correct about the “time” of the explosion. It seems odd, but it doesn’t make physical sense to talk about when something “actually” happened. This is why astronomers always talk about things in “Earth time,” this is, when we actually observed it.
So you're free to invent an absolute time as you did, but when dealing with observations, absolute time cannot exist[^]. But please enlighten me if something in general relativity/more recent theories renders my idea of the universe invalid.
-
Dalek Dave wrote:
Now is Now.
Well, you are right with your idea of now; but I have a different idea of now, and I think it's also valid - it depends on how you think of the universe; for me, observation=event; I can live without absolute time. From http://www.badastronomy.com/bablog/2008/05/14/youngest-galactic-supernova-not-aliens-found/#comment-175177[^]:
Think of it this way: we literally cannot know what’s happening “now” at that distance; we have to wait 28,000 years to find out. In point of fact, there is no “now” at that distance, according to the equations of relativity. Now is simply now, and that means that what we see happening through our telescopes is happening now.
And another comment there:
1. Phil is correct about the “time” of the explosion. It seems odd, but it doesn’t make physical sense to talk about when something “actually” happened. This is why astronomers always talk about things in “Earth time,” this is, when we actually observed it.
So you're free to invent an absolute time as you did, but when dealing with observations, absolute time cannot exist[^]. But please enlighten me if something in general relativity/more recent theories renders my idea of the universe invalid.
Daniel Grunwald wrote:
So you're free to invent an absolute time as you did, but when dealing with observations, absolute time cannot exist[^].
Correct, when dealing with OBSERVATIONS you deal with the time as you see it. But we are not talking about observations, we are talking about the event itself. I grant you that from our perspective it was OBSERVED to have happened 140 years ago, but that has NOTHING to do with when it ACTUALLY happened. These things are important. Quantum Physicists are often trying to recreate things that happened in the first few seconds of the universe, not things that happened last Monday. So when the telescopes are turned to the dark ages of the universe, ie after the backglow of Big Bang went away, but before the first stars shone, they are not talking of things happening now, and their language is not of a present day occurance, but of 13.5 billion years ago.
------------------------------------ "I want you to imagine I have a blaster in my hand" - Zaphod Beeblebrox. "You DO have a blaster in your hand" - Freighter Pilot "Yeah, so you don't have to tax your imagination too hard" - Zaphod Beeblebrox
-
Daniel Grunwald wrote:
So you're free to invent an absolute time as you did, but when dealing with observations, absolute time cannot exist[^].
Correct, when dealing with OBSERVATIONS you deal with the time as you see it. But we are not talking about observations, we are talking about the event itself. I grant you that from our perspective it was OBSERVED to have happened 140 years ago, but that has NOTHING to do with when it ACTUALLY happened. These things are important. Quantum Physicists are often trying to recreate things that happened in the first few seconds of the universe, not things that happened last Monday. So when the telescopes are turned to the dark ages of the universe, ie after the backglow of Big Bang went away, but before the first stars shone, they are not talking of things happening now, and their language is not of a present day occurance, but of 13.5 billion years ago.
------------------------------------ "I want you to imagine I have a blaster in my hand" - Zaphod Beeblebrox. "You DO have a blaster in your hand" - Freighter Pilot "Yeah, so you don't have to tax your imagination too hard" - Zaphod Beeblebrox
OK. But back to the actual topic: From what I've read, the convention for astronomers is to date events by the observation time on earth. This has the huge advantage that they don't need to adjust all their times whenever the distance measurement is improved.
-
Marc Clifton wrote:
I don't recall how many light years it is to the center of our galaxy off the top of my head.
We could ask Chuck Norris. He's driven there and back twice - in a Yugo.
"Why don't you tie a kerosene-soaked rag around your ankles so the ants won't climb up and eat your candy ass..." - Dale Earnhardt, 1997
-----
"...the staggering layers of obscenity in your statement make it a work of art on so many levels." - Jason Jystad, 10/26/2001 -
OK. But back to the actual topic: From what I've read, the convention for astronomers is to date events by the observation time on earth. This has the huge advantage that they don't need to adjust all their times whenever the distance measurement is improved.
As I said in my previous answer... That is for Observations, and I agree with you on this.
------------------------------------ "I want you to imagine I have a blaster in my hand" - Zaphod Beeblebrox. "You DO have a blaster in your hand" - Freighter Pilot "Yeah, so you don't have to tax your imagination too hard" - Zaphod Beeblebrox
-
As I said in my previous answer... That is for Observations, and I agree with you on this.
------------------------------------ "I want you to imagine I have a blaster in my hand" - Zaphod Beeblebrox. "You DO have a blaster in your hand" - Freighter Pilot "Yeah, so you don't have to tax your imagination too hard" - Zaphod Beeblebrox
Another interesting point of view: http://www.badastronomy.com/bablog/2008/05/14/youngest-galactic-supernova-not-aliens-found/#comment-175593[^]
# In our reference frame (and approximately that of the supernova) it is perfectly fine to say that the SN happened 28,140 years ago, but implicit in that statement is the assumption that the one-way speed of light is c. Reasonable though as it is, this is not an observable fact. The observable fact is that the two-way speed of light is c on average. To find the one-way speed of light, you need synchronized clocks at a distance. However, to synchronize clocks at a distance you need to know the one-way speed of light. You can never get around this, not even with slow clock transport (a la Eddington). The Google search term is “conventionality of simultaneity”. [..] Sorry, I forgot to make my point: The point is that you can choose anything for the one-way speed of light, as long as the round-trip time is 2d/c with d the distance. In particular, you can argue that it did not take the light any time at all to span the 28,000 LY (sic!).
It appears that there are infinite valid possibilities for the actual event date, so I'm going to stick with the observations. EDIT: the point of physics is to have a model to predict observations, isn't it? Any talk about non-observable realities sounds like religion to me...
modified on Thursday, May 15, 2008 10:57 AM
-
All time is absolute. If a man sends a signal from the surface of the moon, it take 2.5 seconds to reach earth. That signal is not happening "NOW" it Happened 2.5sec AGO. Unless you have some kind of Alcubierre Drive that we don't know about, I feel you need to think about this. FTL is possible, and indeed a FTL machine has been patented. It really is a simple device. However, back to the point. You are stating that you wish to be living in a Geotemporal Universe, and that would be a REALLY bad idea. For a start, none of the GPS systems would work, as time travels more slowly in orbit than it does on earth, easy to see, there are thousands of corrections to the GPS on board clocks every day. This is substantiated by Relativity, that the Time element of Space/Time is inherant to the localised Gravity Field, and therefore as earth's gravity is not ubiquitous throughout the universe, time cannot be geotemporal. Also if things happened only when we observe them rather than long ago, it means that EVERYTHING we observe in the universe is happening concurrently, and if this were the case, the most distant galaxies would only now be forming! I suggest that if you really think it true then you spend the next 100 years totally rewriting the science of Physics that greater minds than ours have worked on! :)
------------------------------------ "I want you to imagine I have a blaster in my hand" - Zaphod Beeblebrox. "You DO have a blaster in your hand" - Freighter Pilot "Yeah, so you don't have to tax your imagination too hard" - Zaphod Beeblebrox
Dalek Dave wrote:
FTL is possible, and indeed a FTL machine has been patented. It really is a simple device.
Citation please? I'd love to read on this
"Every time Lotus Notes starts up, somewhere a puppy, a kitten, a lamb, and a baby seal are killed. Lotus Notes is a conspiracy by the forces of Satan to drive us over the brink into madness. The CRC-32 for each file in the installation includes the numbers 666." Gary Wheeler "You're an idiot." John Simmons, THE Outlaw programmer "I realised that all of my best anecdotes started with "So there we were, pissed". Pete O'Hanlon
-
Isn't it that the object is 28000 light years distant from our current position? From our perspective/frame of reference the light from the explosion first reached here about 140 years ago. What we see now is the object as it appears now from our reference point. I think the media try to put it as simplistically as possible for headline, audience numbers and sales purposes.
-
Another interesting point of view: http://www.badastronomy.com/bablog/2008/05/14/youngest-galactic-supernova-not-aliens-found/#comment-175593[^]
# In our reference frame (and approximately that of the supernova) it is perfectly fine to say that the SN happened 28,140 years ago, but implicit in that statement is the assumption that the one-way speed of light is c. Reasonable though as it is, this is not an observable fact. The observable fact is that the two-way speed of light is c on average. To find the one-way speed of light, you need synchronized clocks at a distance. However, to synchronize clocks at a distance you need to know the one-way speed of light. You can never get around this, not even with slow clock transport (a la Eddington). The Google search term is “conventionality of simultaneity”. [..] Sorry, I forgot to make my point: The point is that you can choose anything for the one-way speed of light, as long as the round-trip time is 2d/c with d the distance. In particular, you can argue that it did not take the light any time at all to span the 28,000 LY (sic!).
It appears that there are infinite valid possibilities for the actual event date, so I'm going to stick with the observations. EDIT: the point of physics is to have a model to predict observations, isn't it? Any talk about non-observable realities sounds like religion to me...
modified on Thursday, May 15, 2008 10:57 AM
Daniel Grunwald wrote:
the point of physics is to have a model to predict observations, isn't it? Any talk about non-observable realities sounds like religion to me...
Go on then, observe gravity. I can see the effect of gravity, but I can't see the gravity itself, and no-one has ever measured a gravity wave/particle, so gravity a religion? :confused:
------------------------------------ "I want you to imagine I have a blaster in my hand" - Zaphod Beeblebrox. "You DO have a blaster in your hand" - Freighter Pilot "Yeah, so you don't have to tax your imagination too hard" - Zaphod Beeblebrox
-
Dalek Dave wrote:
FTL is possible, and indeed a FTL machine has been patented. It really is a simple device.
Citation please? I'd love to read on this
"Every time Lotus Notes starts up, somewhere a puppy, a kitten, a lamb, and a baby seal are killed. Lotus Notes is a conspiracy by the forces of Satan to drive us over the brink into madness. The CRC-32 for each file in the installation includes the numbers 666." Gary Wheeler "You're an idiot." John Simmons, THE Outlaw programmer "I realised that all of my best anecdotes started with "So there we were, pissed". Pete O'Hanlon
Just something I read years ago... It goes something like this. You build a ring that has a diameter of 1 lightyear. On the inside of the circumference is a string of lights activated by a laser beam set in the center of the ring. You turn on the laser and turn it through 360 degrees in one second. For a whole year the lightbeam flies through space then hits the first detector, then the second and so on until all of the lights have turned on, It takes 1 second for this to happen. For another whole year the lightbeams fly back to the center. Then, all of a sudden the observer sees a line of light appear in the sky, it take one second for that wave of light to travel 3.141 light years! (OK no information is held, and the light beams themselves only travel at whatever value of c you are observing, BUT the wave front of the circle of light is travelling V quickly!) It must be noted that wave fronts CAN travel faster than light, although no individual particle/quanta etc travels above c. (incidentally, cherensky radiation proves particles can travel faster that the light they produce)
------------------------------------ "I want you to imagine I have a blaster in my hand" - Zaphod Beeblebrox. "You DO have a blaster in your hand" - Freighter Pilot "Yeah, so you don't have to tax your imagination too hard" - Zaphod Beeblebrox
-
Wouldn't it make more sense to call it a '140 year old supernova' that's 28000 light years away and the big deal is that we've never seen one that 'young' ? :)
What if there was a SN that occured only 5000 light years away but occured 5140 years ago. It would be a 'younger' SN (by 23000 years) but would be observed concurrently.
------------------------------------ "I want you to imagine I have a blaster in my hand" - Zaphod Beeblebrox. "You DO have a blaster in your hand" - Freighter Pilot "Yeah, so you don't have to tax your imagination too hard" - Zaphod Beeblebrox
-
It happens all the time. My particular bugbear is the use of lightyear as a measure of time or maybe the words Wattage and Ampage, it's a close call.
Russell Jones wrote:
My particular bugbear is the use of lightyear as a measure of time
Yea, it sort of bugs me too. It is understandable given the use of the word year in the name but I cannot excuse it from learned people.
Ant. **I'm hard, yet soft.
I'm coloured, yet clear.
I'm fruity and sweet.
I'm jelly, what am I? Muse on it further, I shall return!**- David Walliams (Little Britain)
-
Daniel Grunwald wrote:
the point of physics is to have a model to predict observations, isn't it? Any talk about non-observable realities sounds like religion to me...
Go on then, observe gravity. I can see the effect of gravity, but I can't see the gravity itself, and no-one has ever measured a gravity wave/particle, so gravity a religion? :confused:
------------------------------------ "I want you to imagine I have a blaster in my hand" - Zaphod Beeblebrox. "You DO have a blaster in your hand" - Freighter Pilot "Yeah, so you don't have to tax your imagination too hard" - Zaphod Beeblebrox
Dalek Dave wrote:
so gravity a religion
It's not a religion, it's a model. And I need to correct this sentence:
Daniel Grunwald wrote:
Any talk about non-observable realities sounds like religion to me...
Of course you can use such things in your model. Only when you start talking about "ACTUAL time" etc., talking like your model is a matter of fact, then it starts sounding religious. But when publishing something like astronomy results, it makes sense to stay with the observable facts rather than relying on some model (if the model is not required at all to interpret the observations). Mark talked about the article like it was bad journalism due to the "140 years ago" issue. I wanted to say that not only the author is not incorrect, he's following the convention used by astronomers and that there are good reasons for that convention.
-
Dalek Dave wrote:
so gravity a religion
It's not a religion, it's a model. And I need to correct this sentence:
Daniel Grunwald wrote:
Any talk about non-observable realities sounds like religion to me...
Of course you can use such things in your model. Only when you start talking about "ACTUAL time" etc., talking like your model is a matter of fact, then it starts sounding religious. But when publishing something like astronomy results, it makes sense to stay with the observable facts rather than relying on some model (if the model is not required at all to interpret the observations). Mark talked about the article like it was bad journalism due to the "140 years ago" issue. I wanted to say that not only the author is not incorrect, he's following the convention used by astronomers and that there are good reasons for that convention.
Daniel Grunwald wrote:
talking like your model is a matter of fact, then it starts sounding religious.
Yep, tell that to the Priests/Imams/Rabbis/any other peddlar of hokey religion. I did not observe god, therefore he does not exist is a good tenet of Atheism, but with gravity, I prefer the faith! :) All said and done though it does not excuse the poor quality of journalism, and they should at least have Science Correspondants with some Scientific Training/Qualification.
------------------------------------ "I want you to imagine I have a blaster in my hand" - Zaphod Beeblebrox. "You DO have a blaster in your hand" - Freighter Pilot "Yeah, so you don't have to tax your imagination too hard" - Zaphod Beeblebrox
-
What if there was a SN that occured only 5000 light years away but occured 5140 years ago. It would be a 'younger' SN (by 23000 years) but would be observed concurrently.
------------------------------------ "I want you to imagine I have a blaster in my hand" - Zaphod Beeblebrox. "You DO have a blaster in your hand" - Freighter Pilot "Yeah, so you don't have to tax your imagination too hard" - Zaphod Beeblebrox
-
Marc Clifton wrote:
it actually happened several tens of thousands of years ago
That's not correct. Your statement sounds like there's something like absolute time. When saying "it happened 28000 years ago"; that implies that it happened at the same time as events on earth that were 28000 years ago. But the only places where that's true are points with equal distance from earth and the supernova; and I don't think those points (probably in the middle of empty space) are particularly interesting... so why use them as reference for your time scale? It makes more sense to use the time on earth, and there "The supernova explosion occurred about 140 years ago" is correct.
It happened 28,000 years ago in our frame of reference. Because the supernova may be experiencing a non-zero velocity relative to us it, itself, may have experienced the blast at a time slightly different than 28,000 years ago (the faster it was travelling the less time it would have experienced since the actual blast). But it was way more than 140 years ago.
cheers, Chris Maunder
CodeProject.com : C++ MVP
