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Hubble vs. Webb - How Far Back Will They See?
Roland Piquepaille writes "According to Forbes, reporting in "Peering Back At The Universe's Past," space telescopes are really acting as time machines. They can watch objects which are so far from us that light has taken billions of years before reaching their mirrors. The Hubble telescope is able to look at events that took place 13.3 billion light-years ago. But the James E. Webb space telescope, currently under construction, and scheduled to be launched in 2011, will be able to see even further and catch phenomena which happened 13.5 billion light-years ago. The astronomers think the Webb telescope might even be able to see up to 13.7 billion light-years ago, when our universe was just 200 or 300 million years old. We are used to see fantastic images from Hubble, without paying too much attention to the characteristics of the telescope itself. So here is a thorough comparison between the two space telescopes."
I think the imagery provided by Hubble to date has been phenominal and expect that imagery from Webb will just as good or better. Looking back that far in the past though is just that ... the past. When we look back and see light that is 13.3, 13.5, or 13.7, or whatever billions of years old, it is exciting and adds more to the knowledge base. However, when I see galaxies that old I can't help wonder if they're still there (probably not) and what has taken their place. What's there now ...
Not trying to offend, I'm genuinely interested. How do they know how far in time they can look with those telescopes? Have photons lost too much energy after that distance?
... that we'll eventually see the big bang? Assuming of course that the theory of the big bang is correct.
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I'm not a that great with science, but isn't the speed of light not actually a constant but changing with the expansion of the universe (only page I could find).
I know many people here are better at science (not to mention spelling, grammer, coding, e.t.c), than I am, so i ask does this not make a lot of these predications less accurate than they might think?
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well, if hubble could actually see as far as (light speed * age of the universe) light years than we could gain new knowledge about the big bang theory and the creation of the universe.
as it is, knowing what the universe looked like at age 300Million is quite nice by itself and simply saying that it "ain't nuttin' new" is quite ignorant!
as the light has traveled millions of light years, we ARE actually seeing something that existed millions of years before our time and thus you could call it some kind of "looking into the past"!
Hubble is 375 miles from Earth, the article has Webb listed as 1 *million* miles from us. Where is it going to be located, and how is it getting there? (I'm guessing that there will be no opportunity for service calls, as there was for Hubble!)
-J
According to the comparison Webb is able to see 13.5 billion light years back in time, not 13.7. And Hubble able to see 13.3 not 13.5.
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I don't understand how we can see so close to the beginning of the universe, unless we have been travelling at a significant portion of lightspeed. Surely the light from events 200 million yrs into the length of the universe should have long since passed this point in space?
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Using faster than light travel (not necessarily traveling faster than c but rather a form of travel which gets you from point A to point B faster than light would travel the distance) and a powerfull enough imaging device you could actually do it. By computing the correct distance and magnificaiton the device would need to be located to zero in on the correct time and then getting your viewer there before the light which started out at the period you wish to view (you would of course also need to find a clear path from Earth to your point with no gravity or objects in the way). Or the much easier example, if we discover distantly located alien life. We could one day show them pictures of their own past, maybe even clear up a few things for thier historians. (Now don't laugh this is all technically possible.)
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You know... I've actually given this some thought before...
Say someday we managed to put out a large mirror...say... X number of lightyears from Earth, where X was half the number of years you wanted to be able to look into Earth's history. Here's what I'm curious about:
1.) Assuming you could get the mirror out there and set up at light speed, it would make sense that the first image of the Earth we would get back was of the craft toting the mirror leaving Earth...well, actually, probably not, since it would logically take some pre-lightspeed travel first. But you get my drift.
2.) Assuming FTL travel, could you actually see into a point in time before the point the mirror left Earth?
3.) What size mirror would be needed for a telescope to be able to capture a reflected image? Would it even be possible? Perhaps with refraction from other celestial bodies (like they've done to enhance Hubble's distance viewing).
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Servicing missions to the Hubble added about 4-5 years of operational life to the telescope and this was possible because being only a couple of hundred miles above the earth, it was accessible.
Obviously, we are human and we can make mistakes. So what happens if there is a problem discovered on the Webb telescope after its launch?
No telescope will be able to look further back than about 300 kyr after the Big Bang. Before this period, background photons were energetic enough to ionise very rapidly any hydrogen atoms that formed, so the universe mostly consisted of free electrons and protons. These are very efficient at scattering light (mean free path very short ~ O(centimetres) ). The universe was opaque to radiation - a glowing fog of photons and plasma.
After 300kyr, the universe had cooled sufficiently for recombination. Virtually all the electrons and protons combined to form neutral hydrogen, which scatters radiation far less well, and the universe became effectively transparent to radiation.
Any attempt to look back will be unable to see anything before this decoupling. We can still see the radiation from the decoupling period in the form of the cosmic microwave background.
Maybe yes, maybe no. We won't know until we look. We've already found structures that weren't supposed to be existing at their 'distance'.
Let's assume there are some aliens out there who want to solve the Kennedy assassination for us next year. At that time, the light will be 42 years out. Assume they want to observe visual light with a resolution of half a meter, which should be enough for a skilled analyst to decide whether the guy on the grassy knoll is carrying a rifle or just a camera.
Unless I flubbed up the calculations somewhere, which is possible, you'd need a telescope with a diameter of 480 million kilometers. Or you'd need two gigantic telescopes 480 million km apart, kept within nanometers of their required position, in order to do interferometry. We don't even have any idea of how to begin to think about designing such a beast. It is theoretically possible, but not within any reasonable realm of practicality for a long, long time.
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Interestingly, it's not as certain as you might think. There's also evidence pointing in the other direction too. COBE's a little too smooth to explain our universe's 'clumpiness'. Then there's the huge galatic walls and voids that appear to be older then the universe. How they could have formed in the currently hypothesised age of the universe is not known.
you are right, of course. But: in this case, the time (in years) you are looking back is *exactly* the distance in light years (by definition of light year). I understood this as an intentional pun pointing out the equivalence (or, more precicely, correlation) of distance you look to time you look back. And, after all, Einstein taught us that time and space are just different sides of the same coin (well, hypercube, actually). so.... just loosen up, ok? don't take everything so litterally.
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What about graviational lensing? I've read suggestions before that the effects of gravity on light mean that every star (or galaxy, for that matter) can be considered a lens, with a focal point somewhere (relatively) near by. If we could find a suitable star, we could simply park a ship near its focal point and pick up the images there.
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but is they can see objects 13.3 billion light years away even correct? since everything is movine away from the 'center' of the universe, 1. wouldn't the objects be farther away? and 2. we are seeing 'back in time' because the light took 13.3 billion years to get to us -- so we are seeing what was there 13.3 billion years ago -- not what is there now (a rather important distinction imho)