While HST’s successor is named after the architect of the revolutionary Apollo Moon missions, an obvious tribute to the National Aeronautics and Space Administration’s second administrator, James E. Webb, the name given is perhaps also symbolic of the aspirations of all those involved in the project, that with the telescope’s launch will dawn a new era in space exploration where insights gained may truly change our experience and understanding of the Universe all over again.
The bigger the project, the greater the preparation. Whether we agree or disagree with this statement we must recognise that if it be true, with its first concept designs beginning as far back as 1989, the James Webb Space Telescope project is certainly one that cannot be accused of underdoing the preparation. In fact as an ambitious international venture so complex and demanding in scope that many of the component technologies have only recently been considered to have attained the necessary level of maturity, it’s little wonder how construction of the world’s next generation telescope only now appears to be embarking on its glorious last lap. So to go right to the heart of the matter, how will the James Webb Space Telescope better the still operational Spitzer Space Observatory (NASA’s current most powerful infrared telescope) and recently upgraded Hubble Space Telescope that it intends to succeed? Well besides being armed with the latest state-of-the art Infra-red imaging instruments the world over JWST will quite simply have a much bigger “optical net” that will dwarf those same light-capturing components belonging to either of its flying predecessors. Once in space, what will be the world’s largest flying telescope ever will deploy to its full size, with 18 hexagonal segments carefully tessellating to make an overall-6.5 metre-diameter primary mirror.
Catching “extra” light from very faint deep-space objects literally makes them easier to see afterwards in the photographs taken by space observatories. However focal length is another important consideration in determining the true abilities of a telescope, for essentially the greater the focal length (ie. combined length of the “cone” of light it can support), the better the resolution of the images it can take. The prestigious focal length of James Webb’s Korsch three-mirror anastigmat telescope will be 131m, no less than double that of Hubble and equal to 13 double-decker buses lined up end-to-end. So where the infrared Spitzer Space Telescope at best can only produce images with blurry glowing splodges of light when it attempts to photograph galaxies as they were 12.7 billion years ago, the infrared Webb Telescope will be able to capture these same galaxies with much greater clarity. JWST’s long-awaited vision however will exceed even this visual threshold.
The telescope of which it is claimed will be able to examine any phase of cosmic history now has four main scientific areas of research written into its ten year astronomical manifesto; The End of the Dark Ages (First Light and Reionisation), the Assembly of Galaxies, the Birth of Stars and Protoplanetary Systems, Planetary Systems and the Origins of Life. Moreover these studies will also include the evolution of our own Solar System. So as telescopes go will JWST be the be all and end all, able to answer every question we have ever had about space, able to target and bring into view any object in the Universe its remote human operators select? Well, not quite. However before an emotion even faintly resembling disappointment passes over any of us, we need to understand that this statement has less to do with questioning JWST’s soon-to-be-proven outstanding abilities as it will the new observatory (along with everyone and everything else) having to work within the laws of physics. We are aware that moving at 300 000km/sec, light is the fastest moving thing known to mankind and that the most distant objects currently visible to us in space are in fact so far away that the quantity of “light years” travelled by photons of light simultaneously become a measure of time in space history. This double-edged unit of measurement therefore reveals to us that a star believed to reside in space at a distance of 1000 light years from Earth, when viewed, is observed not as it is now, but rather as the star looked 1000 years ago since the image of that star travelling across space and arriving in the present has taken 1000 years to reach our eyes.
While celestial objects residing in our own cosmic neighbourhood may or may not be extraordinarily old, (and as such their ages may remain difficult to define with any great accuracy), when it comes to the most distant objects that can be seen anywhere in the Universe, the playing field is quite different. With them we are guaranteed that these deep-space objects must at least be as old as the length of time we know light would take to cross that particular distance, otherwise the “first light” ever to emanate from them would not have yet reached us and so they would not yet be visible. Having established why the most distant objects visible must be among the oldest ever discovered we can now reflect on how the expansion of the Universe is a process in active opposition to our pursuit of observing increasingly ancient cosmic bodies, and by default, our gaining a window into what the cosmos was like in the most distant past. Although the ‘substance’ of space is expanding throughout and in all directions like a fruit loaf rising in the oven, with the sultanas (which remain unchanged in any way themselves) moving farther apart from one another as they are held in the expanding medium of bread, a balloon with black marker dots drawn all over it as it is inflated demonstrates perhaps in a more visual way (albeit on the ‘outside’ only) exactly what happens during the expansion. If with this new example we imagine for the sake of argument that the marker dots drawn on the balloon like the sultanas stayed the same size while the balloon expanded we would also see that because of their close proximity to one another, adjacent dots on the surface of the balloon although evidently having moved some distance away from another by the time the balloon is filled, would not be located anywhere as far from one another as would be one dot in relation to another positioned on the far side of the balloon.
This is what is meant when some say that the Universe is “accelerating” or that the “visible Universe” is receding. The latter reference however explains why the James Webb Space Telescope nor any other observatory for that matter will ever be able to see ‘everything’ in the Universe, because the most distant celestial objects, due to their accelerated rate of separation from us the farther out you go could logically be moving away from us faster than the speed of light. For the keen observer this fatally means that if the image of that distant galaxy or star carried in the light it emits cannot “keep up” with the speed of expanding space then we will never be able to see that object because the image will never be able to reach our eyes.
So will JWST be able to see pretty much all in the ‘observable’ Universe? Yes, but for the moment only because that which is observable is changing due to space expansion. Or to put it another way, will the James Webb Space Telescope or any other observatory for that matter ever be able to see everything that was or may ever have been in the Universe? The answer to that question is no, because 14 billion years ago or farther back in history whatever ultra-distant objects may have existed would now, at this advanced stage in the expansion of the Universe, be rushing away from Webb so fast it will never have the opportunity to see them.
(Part Three to follow)
(Article by Nick Parke, Education Support Officer)