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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."
As I'm sure everyone will be quick to point out, lightyears isn't a measure of time, rather of distance.
It is more accurate to say that the hubble could see images 13.3 billion years ago, and the Webb telescope may be able to see images 13.7 billion years ago.
Somebody place a mirror on the other end!
Then we can look into the history of our own Earth!
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13.5 billion light years ago? Maybe I am being stupid, but I always thought that a light year was a measurement of distance?
if they could only see a few days back and tell me where I left my mobile phone.
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What truth?
There is no dupe
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 ...
13.7 / 13.3 = 1,030075188 => 0.03 % performance increase with the new, latest, more expensive system.
Nahh, I'll maybe void my warranty, but I'll just increase the fsb of my old Hubble...
Anyone has tips on deep space overclocking ?
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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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is the fact that while Hubble can view things in the optical, James Webb will be looking at things in the infra-red. The two Wiki links (from the article) provide much more information.
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/. is screwing up the text, but the links should still work.
http://en.wikipedia.org/wiki/James_Webb_Space_Tel
http://en.wikipedia.org/wiki/Hubble_Space_Telesco
Grr...
It's rather more complicated than you think. The light reaching the telescopes is x billion years old, meaning that the objects that emitted the photons have long since moved elsewhere and are no longer there where the telescope sees them. So, when looking out into the universe, you are seeing mirages of the past. The more distant the object, the older its light. So yes, telescopes are time machines in that regard because such is the nature of spacetime - if you look over any given distance you are in effect looking into the past.
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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"!
Dear Sir,
Some of us prefer the universe the way it is, more mature and filled out. I think its disgusting that these perverts want to spend so much money to ogle at the universe when it was a young hottie.
No doubt they are also hoping to get a glimpse of some of the banging the universe got up to in the exuberance of youth.
Shame on you all I say.
Yours etc.
Outraged
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What truth?
There is no dupe
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
I worked on the Webb telescope project for a short period of time (back when it was Next Generation Space Telescope) and, believe me, they had a hard enough time scrounging up the money to create what they have now. Making the mirror "a little bigger" or increasing the size of the infrared array would require much more effort than you might think.
http://www.astronomycafe.net/qadir/acosmbb.html
Just for the record, the Big Bang theory is becoming as accepted in cosmology as the theory of evolution is in Biology.
There will eventually be a limit to how far back we can look in time. The Big Bang itself will just appear to be an incredible brilliance everywhere.
That same brilliance has cooled to the point that nowadays, it's only detectable as an almost-universal background microwave radiation.
The detection of that radiation is considered one of the strongest "proofs" of the Big Bang theory, by the way.
There is an optical limit or boundary which cannot be seen past - the surface of last scattering - preventing you from actually seeing right to the beginning.
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isn't the speed of light not actually a constant but changing with the expansion of the universe
Short answer no, longer answer we don't know. Pretty much all of modern physics is built off the idea that the speed of light is a constant. If you start changing the speed of light then all sorts of thing "break" like conservation of energy. So if you can change the speed of light, you could create matter out of nothing. Neat trick if you could pull it off. That said changing the speed of light does solve some nasty problems surrounding the big bang.
There's also the question that if the speed of light was changing if we'd even have any way of noticing because everything would be skewed along with it. Fun stuff.
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13.7 / 13.3 = 1,030075188 => 0.03 % performance increase with the new, latest, more expensive system.
As another poster has pointed out, it's actually a 3% improvement.
The point is, that's only 200 or 300 million years from the very beginning of the universe, and it gets exponentially more difficult the further back you want to see.
Rather than 13.7 vs. 13.3 billion years back from now, think 200/300 million years from the start versus 600/700 years from the start. That's a pretty good improvement.
The article states that the new 'scope costs about the same as Hubble, but will only have a 10-year lifetime, while Hubble is expected to be in service for 20 years.
Surely modern manufacturing etc should be able to improve on Hubble's lifetime for the same money? What am I missing?
A light year is a valid distance measurement since the speed of light is a constant. It's as valid as defining the distance between home and work as "10 minutes in my car travelling at a constant 60 mph".
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...is an interesting thing, but a problem remains: it can't see events in the present (at far distances, obviously).
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?
The orbit is about 1.5 million km distance from the earth, at something called the L2 Lagrangian. The Webb wiki page has a link to the Lagrangian page, but for the lazy people, it's here. The orbit was chosen to keep the position of the sun constant relative to the telescope, so that the big 'parasol' can be used to shield the infra-red sensor.
As for Hubble, it's been able to give some awesome images, but it has its limits. I was hoping that the JW (henceforth called J-Dubya?!) would be able to start spotting planets around other stars, but it's not designed for that. I'd like to know if it's theorically possible to keep both in orbit and use them in parallel somehow, in the same way that ground-based radio telescopes have been linked together in arrays. Probably not worth the hassle?
The 'infra-red only' sensor troubles me. Since the telescope's aim is to study the Big Bang, the light/photons it'll be receiving will have travelled for a long time/distance and I guess be red-shifted way down to the IR band. This is all very well, but it means that the telescope shouldn't be considered as a replacement for Hubble, which carries out a wider range of observations.
As an aside, I believe that there is a limit to how far back we can look. At some point, probably less than 1 million years (a guess, can anyone help?), the universe was just too dense for photons to travel around unhindered as they seem to these days. Who said it was better back in the old days eh?
Now two questions. First why beryllium? I know that it's lightweight so easier to lift into orbit. Any other reasons? And secondly what happens if a micro-meteor hits this shield? Do we get a permanent bright spot on all subsequent images, like a broken pixel on an LCD display?
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You're imagining the Big Bang as an explosion taking place in space. In this view there is an infinite, empty expanse of space, in which there is an explosion at one point which throws out all the material in the universe.
This view is wrong. If it was correct the galaxies would form a roughly spherical shell around an empty central region, at the very centre of which would be the Big Bang's 'ground zero'. We would therefore expect to see a great clustering of galaxies when we looked along the surface of this sphere toward our neighbours, and a great empty darkness 'above' and 'below' us. But this is not so; in fact the galaxies are very evenly distributed throughout all of observable space.
The Big Bang is more correctly viewed as an explosion of space, rather than in it. The Big Bang takes place simultaneously at all points in space, and it is space itself that expands thereafter, spreading out the contents of the universe and cooling the hot gas.
As a result, the light emitted from our region of the Universe in the Big Bang has indeed long since left the area, but we are now able to see the light emitted from the Big Bang in regions that are now some 13.7 billion lightyears away. Of course at the time they were much nearer than that...
We have, in fact, seen the Big Bang, or at least seen as close to it as we can ever hope to achieve. In the very early stages of the Universe, light could not propagate far; the universe contained a hot, dense gas of charged particles which was opaque to light. Once the electrons and protons combined to form hydrogen atoms, the gas became transparent and the light was released. This light has been greatly redshifted by the enormous expansion of space, and is now detected as a background glow of microwaves at a temperature of about 3 kelvin.
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Seeing 'back in time' has little or nothing to do with magnification.
The important factor is collecting enough light from a very faint source.
So the area of the mirror, the sensitivity of the camera and the directional stability of the system over time are what counts.
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Anybody else notice that Webb is expected to have a lifetime ten years shorter than Hubble?
I'd have expected a more recently built telescope to last longer than an older one.
Also, anybody have a clue exactly what happens when a telescope dies?? (Visions of Hubble slowly growing incontinent etc.....)
I'm going to butcher the explanation, but modern cosmology posits that there is no center to the universe in the way you mean.
It's important to remember that at the moment of the big bang, there wasn't a universe outside of it. That is to say that when the big bang occured, it didn't expland into some already exisiting space, rather it was the space that was expanding. As such, all objects are moving away from all other objects.
http://www.astro.ucla.edu/~wright/nocenter.html
has a decent drawing to illustrate how this leads to no "real" center.
The other explanation that has always helped me picture it is to imagine the universe as an un-inflated balloon. In this model, we've reduced the universe to a two-dimensional, unbounded, infinite space in order to help us visualize this principle. Before inflating the balloon, mark several points with permanent marker, Now, when you inflate the balloon, you can see that each point grows more distant (over the surface of the balloon) from every other point you've marked and that the farther one mark is from another, the faster it moves away from it. From the point of view of a given mark, everything else is moving away from it, which would give the impression that it's at the "center" of the balloon's surface. At the same time, however, that impression would appear to be true for every other mark.
This is a tough one to comprehend but heres a shot. It doesnt matter where you look. Its everywhere, and here is why:
When you look away from the earth, you are looking back in time. This is due to the fact that photons travel at the speed of light. So if you look at the moon, you see the moon a half a second ago. Mars is several minutes ago. Alpha Centari is about a year ago. So the futhrer out you see, the further back in time.
Now think of the universe as expanding. If you look out a to a distance where the light is half as old as the universe, you see the universe as it was at that time. But the universe was much smaller then so the galaxy you look at seems bigger than it should given how they look today. So the expansion of the universe and the traveling of photons acts as a lense making things look bigger as you look back further (theres less universe to fill the sky so objects look bigger).
OK so then you look all the way back. The big bang then fills the sky. It is everywhere. And we see it. Its what is refered to as the 3 degree Kelvin background radiation. And in the radio, no matter where you look, you see it.
Now this is not actually the big bang itself. The universe was too dense for anything to be seen. So what we see is what is referred to as the universe at the time of last scattering, when the light from the big bang was finally able to escape as the universe had expanded enough that it was not so dence to capture all the light. So when you hear about people studying the fluctuations in the background radiation, they are actually studying this period of the universes expansion.
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Astronomers have a whole range of different ways to measure distances, each of which works in a different regime. They form a "cosmological distance ladder" - you attempt to calibrate each new method during its overlap region with the previous method.
Parallax is the method for the very shortest distances (nearby stars).
For intermediate distances (distant stars in our own galaxy, relatively nearby galaxies), most of the methods come down to finding some sort of "standard candle" - something that you know the intrinsic brightness of, so you can use its apparent brightness and the inverse square law to calculate its distance. Astronomers tend to use particular types of variable stars (stars with a well-defined cycle of brightness changes) for this purpose. For galaxies, you can sometimes use averaged properties of all the stars to estimate the distance.
For cosmological distances (very distant galaxies) the most common trick is to use redshift. Because of the universe's expansion, an object twice as far away is receding from us twice as fast, and so its light is Doppler-shifted twice as much. Ideally, you look for known features of the object's spectrum and see what wavelength they have ended up at. This is what people are talking about when they measure the distance to Hubble's latest find.
There is also a complementary method that uses standard candles at cosmological distances. In this case, you use Type Ia supernovae, a particular type of exploding star that looks pretty much the same every time. They're bright enough to be seen very far away, and again you can get the distance using the inverse square law (modified by general relativity). It's the difference between this method and the redshift method that provides the strongest evidence for dark energy - it shows us that the universe is expanding faster than we expect, and that this expansion is accelerating.