The Physics Factbook
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Wahlin, Lars. The Harmonic Universe [pdf]. The Deadbeat Universe. Boulder, Colorado: Colutron Research, 1997: 27.  "Total Mass of the Universe within x_{0}: M_{u} = x_{0}^{2}a_{0}/G = 1.59486 × 10^{55} kg"  1.59486 × 10^{55} kg 
Hopkins, Jeanne. "Universe." Glossary of Astronomy and Astrophysics. Chicago: The University of Chicago, 1980: 183.  "The total proper mass content of about 10^{23} M (Sandage derives 10^{56} g from his determination of the deceleration parameter q_{0}) and radius of about 2 × 10^{28} cm are the order of magnitude that most cosmologists would accept if the universe is bounded. Total mass contributed by luminous matter, about 3 × 10^{53} g."  3 × 10^{50} kg 
Nielsen, Louis. The Extension, Age and Mass of the Universe, Calculated by Means of Atomic Physical Quantities and Newton's Gravitational 'Constant'. Rostras Forlags. 20. November 1997.  "The value of R is  also in the established cosmology  determined to be of the order 10^{26} m and M_{0} is in my quantum cosmology calculated to be about 1.6 · 10^{60} kg, a value I calculate based on a 'measured' relative variation of Newton's gravitational 'constant'."  1.6 × 10^{60} kg 
Lang and Gingerich. A Source Book in Astronomy and Astrophysics. Massachusetts: Harvard university, 1979: 724.  "M = 1.8 × 10^{57} g"  1.8 × 10^{54} kg 
Immerman, Neil. Sacramento Peak: The Universe. University of Massachusetts Amherst. 21 May 2001.  "This critical mass density is currently equal to 6e27 kg/m^3. If the Universe is at the critical density, then the total mass of the Universe is closer to 1e53 kg, and the number of atoms (assuming that most of the mass is in the form of hydrogen atoms) about 6e79."  10^{53} kg 
Ryden, Barbara. Lecture 40: Curvature of the Universe. 6 March 2003.  "'Only two things are infinite, the universe and human stupidity  and I'm not sure about the former.'  Albert Einstein"  ∞ 
What is the universe? Wikipedia defines it as "the summation of all matter that exists and the space in which all events occur." Since the universe contains matter it has a mass.
The question of 'What is the mass of the universe?' has been asked for many years. The answer, which is very complicated, has been derived, or at least attempted to be derived by few. There are many constituents of the universe which can make the total mass of the universe questionable. Some researchers have said that up to 95 percent of the total mass of the universe is made up of dark matter. Because dark matter cannot be detected directly, but is known to have more mass than visible matter, it cannot be measured and numbers based on dark matter are guesses. Since the approximate size of the universe is also not concrete, scientists have dispelled the notion of calculating the mass by measuring one section of the universe and multiplying it by the approximate value for the size.
The calculated mass of the universe ranges anywhere from 10^{53} kg to 10^{60} kg. Since different methods were used, the disparity between the numbers is so great. No one actually knows what is out in the universe. Although many scientists would love to find an exact number, they have already started calculating how much it all weighs. Because no one knows an actual number, we can more likely agree that since the universe is still expanding, the mass is infinite.
Kristine McPherson  2006
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