View Full Version : Is it real
Just Curious
11-26-08, 08:27 AM
When you observe the night sky on a clear night you see thousands of stars. But because of the vast distances it takes light from them years to reach us. In fact our nearest star is 4.5 light years away. This means that some of the stars that we see are not actually there anymore. They blew up years ago but because the light from them is still travelling towards us we think they are still there. How do astronomers make any sense of what they are looking at when they don’t know whether they’re real or not? If our nearest star blew up today we wouldn’t know it for 4.5 years. More to the point, if we sent up a rocket to travel to our nearest star and orbit it sending back information, it may get there and find it’s gone. Discuss………
cosmictraveler
11-26-08, 08:41 AM
How do astronomers make any sense of what they are looking at when they don’t know whether they’re real or not?
But at one time they were real don't forget, or that star light would not exist at all.
we sent up a rocket to travel to our nearest star and orbit it sending back information, it may get there and find it’s gone. Discuss………
That is why we send robotic spacecraft out to search BEFORE we send humans!
imagine this...instead of stars...you would see past humans of Earth...in the distance...civilizations that existed on Earth many million years ago and elsewere...your ancestors smiling at you, not knowing you can see them and what they do.
Imagine, if we could have a telescope powerfull enough to see not just the stars and planets many million lightyears away...but also people on those planets...
many million years ago...what happened.
And someone is looking at us now...from the future...million years into the future they are looking at us, at our Earth. Perhaps we ourselves have traveled far into the galaxies and decided to look back at Earth as it was million years ago...now in year 2008.
Imagine...
Just Curious
11-26-08, 08:49 AM
That is why we send robotic spacecraft out to search BEFORE we send humans!
But the signals from the robotic spacecraft would take 4.5 years to get back the message to us that it was alright to blast off with humans. In that time and the years it would take to get there the star may be gone.
may be gone? They will be gone...unless we design a time-machine of a kind.
cosmictraveler
11-26-08, 08:52 AM
That is why we send robotic spacecraft out to search BEFORE we send humans!
But the signals from the robotic spacecraft would take 4.5 years to get back the message to us that it was alright to blast off with humans. In that time and the years it would take to get there the star may be gone.
Scientists can tell if a star is still there or not today before they send a robotic spacecraft anywhere.
tablariddim
11-26-08, 08:52 AM
I thought that scientifically speaking the future cannot actually exist in the same time/space continuum that we are in, in the present.
Thing is...lets just say we design a spacecraft able to travel lightspeed...than it would take million of years to travel there.
Okay...we design a spaceship that can use curvatures in space to cut time considerebely and make holes in space time continuum...okay than we arrive there at the time of million years past what we saw...so we are still million years late...even if we arrive instantaneously to what we see in our telescope to that location.
The only way we can ever travel there is if we design a time machine. Is that even possible? I have no idea. Black Holes seem to be a candidate for something relating to time...but that is all theories.
Just Curious
11-26-08, 08:54 AM
Or we may bump into a star that's only just been born but we didn't see it at the time of launch. That's why I ask myself if anything is real when I look up at the stars
cosmictraveler
11-26-08, 08:55 AM
Or we may bump into a star that's only just been born but we didn't see it at the time of launch. That's why I ask myself if anything is real when I look up at the stars
Stars are "born" in Nebulas, so just avoiid any Nebulas along the way and things will be fine. ;)
Just Curious
11-26-08, 08:56 AM
Scientists can tell if a star is still there or not today before they send a robotic spacecraft anywhere.
I wish you could supply proof of this because it's at the heart of my problem
well its all real "Just Curious"
I mean do you consider yourself and Earth as real?
Because million years into the future light from Earth will reach some planet million light years away and they will see us currently as we are, and they will ask the same question "is it real?" And guess what their' planets light will reach some other planet million light years away and they will see them us they currently are, and they will ask the same question "Is it real?" And guess what their' planets light will reach some other planet million light years away and they will see them us they currently are, and they will ask the same question "Is it real?" And guess what their' planets light will reach some other planet million light years away and they will see them us they currently are, and they will ask the same question "Is it real?" And guess what their' planets light will reach some other planet million light years away and they will see them us they currently are, and they will ask the same question "Is it real?" And guess what their' planets light will reach some other planet million light years away and they will see them us they currently are, and they will ask the same question "Is it real?" And guess what their' planets light will reach some other planet million light years away and they will see them us they currently are, and they will ask the same question "Is it real?" And guess what their' planets light will not reach anyone...because the universe will start contracting again and the cycle will repeat forever...Big Bang...expansion...contracting...infinite density...Big Bang...expansion...etc...
Scientists can tell if a star is still there or not today before they send a robotic spacecraft anywhere.
I wish you could supply proof of this because it's at the heart of my problem
well my question to all the physicists is...do gravity act instantaneously? Because every object in our universe has some sort of gravitational influence on all other objects...so is this star thats light million of lightyears away has reached us but in reality the star is gone...does its gravitational field still act? :shrug:
Just Curious
11-26-08, 09:04 AM
dragon: I'm not questioning whether I am real or any star is real. Of course they are all real at some time. My question is about time frames. Are we all real in any specific time frame. The answer is no.
And my statement is that we are real to whatever the relative view is. That is why Einstein relativity was recognized as the millenium's most important scientific achievement.
Just Curious
11-26-08, 09:08 AM
well my question to all the physicists is...do gravity act instantaneously? Because every object in our universe has some sort of gravitational influence on all other objects...so is this star thats light million of lightyears away has reached us but in reality the star is gone...does its gravitational field still act
dragon: you are now asking the question that Einstein asked and the answer is no. Gravity can't act instantaneously. That is why Newton's Laws of gravity fall over at huge distances. Curved spacetime is the answer.
cosmictraveler
11-26-08, 09:12 AM
Scientists can tell if a star is still there or not today before they send a robotic spacecraft anywhere.
I wish you could supply proof of this because it's at the heart of my problem
http://www.google.com/url?sa=U&start=6&q=http://www.bluffton.edu/~bergerd/NSC_111/stars.html&ei=9VstSfSlOpCu8QSNlPjiCg&usg=AFQjCNG6ZkkOKOF6lo_uJoc0Kk1QFTF4QQ
Just Curious
11-26-08, 09:28 AM
Useful link. So basically scientists can observe whether the star is about to burn out now or millions of years in the future and thus determine from its distance whether it's likely to still be there when the spaceship arrives.
Fraggle Rocker
11-26-08, 10:52 AM
When you observe the night sky on a clear night you see thousands of stars. But because of the vast distances it takes light from them years to reach us. In fact our nearest star is 4.5 light years away. This means that some of the stars that we see are not actually there anymore. They blew up years ago but because the light from them is still travelling towards us we think they are still there. How do astronomers make any sense of what they are looking at when they don’t know whether they’re real or not?Regarding any individual star, obviously the older it is the less we know about its current state and it may not still exist. But regarding the universe as a whole, we have a great deal of information. The time lag is actually very useful. We can see with our own eyes (well with our instruments anyway) that stars, galaxies and other cosmic entities behaved exactly the same 12 billion years ago as they do now. So we can be confident that the motions and thermodynamic behavior of the distant objects are predictable. We can anticipate their locations, the speed of their decay, etc. Soon we will probably be able to predict their likelihood of having planets, even earthlike planets.
Of course this doesn't do us much good in reference to any individual star, but that can't possibly matter because it's unlikely that we'll ever be able to travel that far. The closer the star, the greater the probability that we may some day have a technology to visit it, but also the greater the probability that it won't have changed much from the image we receive from its lightwaves today, and in fact will be pretty close to the same place.
Unless relativity is disproven and there's a way to break the lightspeed limit, there will never be a significant level of interstellar travel or even communication, much less the "galactic civilization" that science fiction writers create. We'll be lucky to have access to the closest 50 or 100 stars. Perhaps generation starships or unmanned probes can go farther, but the farther they go, the longer it will be before we hear back from them--I mean like tens of thousands of years longer. This is not the way to build up a fascinating database of interstellar geography and to discover exciting new civilizations.
As for traveling outside our own little galaxy, forget it! A round-trip to the other side of our own galaxy, at lightspeed, would take just about a quarter of a million years. Human civilization is only ten thousand years old.If our nearest star blew up today we wouldn’t know it for 4.5 years. More to the point, if we sent up a rocket to travel to our nearest star and orbit it sending back information, it may get there and find it’s gone.Gigantic objects like stars do not work that fast. It's extremely improbable that a star that we can see today and is in the prime of health will pass into another stage of its evolution and be impossible to find in just four short years. The signs of its impending doom would have been visible to our earliest sophisticated equipment; maybe even to Galileo.well my question to all the physicists is...does gravity act instantaneously?Then you should be asking this question on the Physics board, not the Astronomy board. I'm not a physicist or an astronomer, but I tried Googling the topic. It is way over my head. Apparently the answer is "yes and no."
cosmictraveler
11-26-08, 11:47 AM
Useful link. So basically scientists can observe whether the star is about to burn out now or millions of years in the future and thus determine from its distance whether it's likely to still be there when the spaceship arrives.
Yes. That link supplies you with many answers to your query.
eburacum45
11-27-08, 10:40 AM
The vast majority of stars in the sky would still be there if we had the means to travel to them at the fastest speed possible, that is, at the speed of light. Take Alpha Centauri for example; it is only four light years away, but is expected to persist for at least a couple of billion years more. The same can be said for all of the (approximately ) nine thousand stars which can be seen with the naked eye from Earth, with very few exceptions.
One particularly bright exception is Betelgeuse, probably about 600 light years away. This star is so unstable that there is a slight, but real chance, that the star has already exploded, and the light is somewhere on its 600 year journey to Earth. A very few others are in the same boat (Rho Cassiopeia, Kappa Cassiopeia are two possibilities) but that is about it. So out of the thousands of stars you can see with your naked eye, only two or three stars are no longer around. And quite possibly even those stars are still there.
Human civilization is only ten thousand years old.
Humans however have existed for 200 thousand years
( agree with the rest fraggle)
well my question to all the physicists is...do gravity act instantaneously?
Gravity is a tricky subject, because we still have no idea what gravity really is. All we can do is very accurately model its effects, exactly what's involved in creating these effects is still up for debate.
If you have specific questions try www.madsci.org, it'll be answered by actual physicists. There's a few actual physicists on this board too though.
As for traveling outside our own little galaxy, forget it! A round-trip to the other side of our own galaxy, at lightspeed, would take just about a quarter of a million years. Human civilization is only ten thousand years old.
Of course for the person doing the traveling only a few years would pass. If we could travel at a hair less than light speed then sending colony ships to the other side of the galaxy would be possible, we'd just never hear from them again back on Earth because from our frame of reference their trip would take, as you said, tens of thousands of years.
James R
11-28-08, 12:17 AM
well my question to all the physicists is...do gravity act instantaneously?
That's a question with two different answers. Once a gravitational field has been "set up" in the vicinity of a massive object, other objects in the field essentially feel the gravity instantaneously. Thus, the Earth feels a constant gravitational "pull" towards the Sun.
But changes in gravitational fields are thought to be carried by gravitational waves. Gravitational waves have not been detected yet, but they are predicted to travel at the speed of light. So, if the Sun disappeared right now, the Earth wouldn't "know" about the gravitational change for 8 and a half minutes - the time it takes light to travel from the Sun to the Earth.
Things get even more difficult when we start to ask questions such as "Does the gravitational field vector from the Sun acting at the Earth point to where the Sun is in space now, or where the Sun was 8 minutes ago? And does this affect the Earth's orbit?"
I used to know the answer to this one, but I can't recall now.
Does the gravitational field vector from the Sun acting at the Earth point to where the Sun is in space now, or where the Sun was 8 minutes ago? And does this affect the Earth's orbit?"
Annybody knows the answer to this?
Naively, the finite propagation speed of gravity would suggest that the Earth is attracted to where the Sun was eight minutes ago. Using this aspect of GR only would result in unstable orbits; this is a straw man version of GR used by many a crackpot to 'debunk' GR. Other aspects of GR (gravitomagnetism and velocity-dependence) act to nearly cancel the apparent phase delay: The net result: The earth appears to be 'attracted' (quoted because gravity is not a force in GR) to very close to where the Sun is now rather than where it was 8 minutes ago.
Fraggle Rocker
11-28-08, 12:41 PM
Humans however have existed for 200 thousand years ( agree with the rest fraggle)Sure. But civilization is what provides the economies of scale and the division of labor that generate an economic surplus and make it possible for people to specialize in science, engineering, the arts, teaching, etc. The entire scope of our history as a people with governments, metallurgy, writing, schools, and finally science and electronics is only ten thousand years. A round trip to the other side of the galaxy in a relatively tiny (compared to the inhabitable area of a planet) generation-starship will take at least twenty-five times that length of time. During all that time the ship will have to be kept running (landing to pick up raw materials about once per century), and civilization itself will have to be maintained (with only a narrow bandwidth of communication with the home world and an increasing time lag that will make actual conversation impossible). That's quite a project to plan!
Sure. But civilization is what provides the economies of scale and the division of labor that generate an economic surplus and make it possible for people to specialize in science, engineering, the arts, teaching, etc.
I think I get your point
I secretly hope that one day we will be able to make wormholes and move them at sublight speed with light weight unmannend ships to other stars
some papers claim they could sustain wormholes with a infinitly little exotic matter (I'm thinking casmir effect that creates negative pressure) but the subject is to complex for me (and 99,99% of the rest of us).
Still...
It's a way to reach the stars
Scientists can tell if a star is still there or not today before they send a robotic spacecraft anywhere.
I wish you could supply proof of this because it's at the heart of my problem
Some 70% of the stars in the universe are dwarf stars. These have lifetimes of billions and billions of years, so are a safe bet they will still be there when we arrive. Presumably you mean the planets orbiting these distant stars will still be there and not destroyed when their parent star goes nova/supernova?
Something strange. Have you seen a good picture of the Andromeda galaxy? It's two million light years away but more importantly it's 200,000 light years in diameter. Since the galaxy rotates, we look at the far side, we are seeing it 200,000 years later than the near side, so it has rotated in that time. Maybe we are looking at the same part of the Andromeda galaxy on both sides of it?
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