Lowest Density in Universe ``` Name: Raymond Status: student Grade: 6-8 Location: MI Country: USA Date: Winter 2013-14 ``` Question: Is it possible for there to be an area of space where there is nothing; no particles or atoms and nothing around the "vacuum" to be sucked in? If no, what is the lowest condensed area of space ever recorded? Replies: Dear Raymond, The largest areas of emptiness would lie between the clusters of galaxies. David H. Levy Raymond, From a science perspective, any answer to this question would have to be backed up by data. Let us say we tried to create a "total vacuum" in a lab on Earth. The immediate next question will be, how do we know that there is a complete vacuum in the container. No matter how good our instruments are, it will have a lower limit in its accuracy or certainty - and we can only say, for example, that in a space of say 100 parts, there is no particle that is 1 part in size. But, taking this example, because of the limitations of our instruments, we cannot say that there is no particle that is 0.1 part in size within those 100 parts - or another way to put it, that in 1000 parts there is no 1 part particle size. In real terms, we might be able to say that we created a space that our instruments are capable of telling us that there is no single atom in every 1 Liter, but if the space we created is 10 Liters in size, then our instruments cannot tell us if there is a single atom in that space. Another way to put this, if we created a 1 Liter space and our instruments are capable of telling us that there is nothing the size of an atom in it, it could also happen that our instruments are not good enough to tell us that there is nothing of the size of an electron (which is far smaller than an atom) in that same space. So, to summarize, being able to say "total vacuum" is really dependent on the certainty of our instruments. Greg (Roberto Gregorius) Canisius College Hi Raymond, Thanks for the question. One of the places in space with the least number of gas particles, or any other particles for that matter is in the "wake" of a satellite. I put "wake" in quotes since there is very little behind the satellite. In fact, the areas of space behind satellites have been used in studies which need an almost perfect vacuum. I hope this helps. Thanks Jeff Grell Raymond Very small question about a very large space :) The lowest density in space is probably absolutely zero, somewhere given the immensity of the universe, but since we haven't been everywhere in space, I do not know how we could say with certainty. I do not know of any density measurements in our history of space exploration. Before, a couple of years ago, we assumed space was a perfect vacuum, but since then we have concluded that there must be dark matter and dark energy in the universe. That constitutes about 70 % of the universe which is the same proportion of land to water on Earth so we are dealing with a great uncertainty here. We deduced the presence of dark matter and dark energy (matter and energy are interchangeable in accord ance with Einstein's formula E=mc2 ) from the fact that the universe's expansion is accelerating and that there must be some as yet undiscovered Energy/Matter source that is driving it. Sincere regards, Mike Stewart Click here to return to the Astronomy Archives

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