While I understand what they mean...
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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.
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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
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"...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
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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
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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
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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.
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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
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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
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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
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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)
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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.
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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
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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
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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
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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
Dalek Dave wrote:
I did not observe god, therefore he does not exist
Yeah, that's Atheism as religion, sadly all too common. I prefer: I did not observe God, therefore I don't need him in my model of the universe. Special relativity works fine without absolute time (which cannot be directly used for observations anyway), so I don't need it. Keep it simple. But obviously there are observations for which special relativity doesn't work, it just happens to be the model that I'm most comfortable with. I guess should spend the time to learn more about modern physics. But the more accurate a model is, the more complicated it seems to be. Maybe the universe is infinitely complex, so that no (finite) model can completely describe it (think Gödel's incompleteness theorem[^]), maybe every physics law having an "exception" law, just like a good bureaucracy? :-D Back to topic: That's why I asked: is absolute time useful (or maybe even necessary) for a modern theory? "Useful" means for me that it makes the theory simpler.
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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
That's not younger, it's just closer.
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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
That's a convoluted demonstration of phase velocity not group velocity. A simpler representation of the same thing can be done by observing a sweep of a laser from a large distance. Phase velocity can be arbitrarily high, but despite hordes of tech illiterate science writers getting it wrong has absolutely nothing to do with the light speed limit, nor can it be used to circumvent it in any way to travel or send data faster than it. http://www.geneseo.edu/~freeman/animations/phase_versus_group_velocity.htm[^]
You know, every time I tried to win a bar-bet about being able to count to 1000 using my fingers I always got punched out when I reached 4.... -- El Corazon
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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.
Space and time are just different axes of the same thing by relativity. Everything moves through spacetime at the speed of light. Normal objects travel with a velocity of ~1 (lightyear/year, second/second, meter/meter, etc) in time and ~0 in space.
You know, every time I tried to win a bar-bet about being able to count to 1000 using my fingers I always got punched out when I reached 4.... -- El Corazon
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No, it Really happened 28140 years ago. Someone on a planet half way between us and them would have observed it 14000 years ago. A planet 141 lightyears further away would observe it next year. Since it can't have happened more than once, it MUST have happened 28140 years ago! There is a difference between Event and Observation. You see a footballer kick a ball, but hear it a second later. Did he kick it twice? I don't think so.
------------------------------------ "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:
No, it Really happened 28140 years ago.
No, the way you're arguing it really happened about 28,000 years ago. Remember significant figures people. Unless the 28,000ly distance is known to ~.25% accuracy or better, adding 28,000 and 140 gets you 28,000 out. IF the error is larger than the quantity being added the result remains the same.
You know, every time I tried to win a bar-bet about being able to count to 1000 using my fingers I always got punched out when I reached 4.... -- El Corazon
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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.
That's what got me all confused yesterday. For me, it's a measure of distance. But it's also relative to time. The heading should've been "A supernova that occured 140 years ago at a distance of 28,000 light years" I can't stand the "wattage and ampage" either!
