Department of Energy Argonne National Laboratory Office of Science NEWTON's Homepage NEWTON's Homepage
NEWTON, Ask A Scientist!
NEWTON Home Page NEWTON Teachers Visit Our Archives Ask A Question How To Ask A Question Question of the Week Our Expert Scientists Volunteer at NEWTON! Frequently Asked Questions Referencing NEWTON About NEWTON About Ask A Scientist Education At Argonne Constant Number of Atoms

Name: Nigel
Status: student
Grade: n/a
Country: United Kingdom
Date: Spring 2012

Why is it that a liquid in a container cannot flow from bottom to top even though there is a pressure difference?Is the number of atoms in the universe fixed?

No. New atoms are constantly being made by fusion inside stars, including our sun. So that means overall that the number is probably decreasing over time.

Richard E. Barrans Jr., Ph.D., M.Ed. Department of Physics and Astronomy University of Wyoming

No. Atoms can split into two or more smaller atoms, and they can fuse together into larger atoms.

Tim Mooney


On our Sun alone, two Hydrogen atoms are being converted to one Helium atom.

Our universe is expanding and that rate of expansion is accelerating. So there must be some energy source that we cannot see that is driving this acceleration. Since mass and energy are interchangeable by a factor of the speed of light squared (E=mC2) Scientists believe that there is inter galactic matter that we cannot see (dark matter) that is converting to the energy that supports the accelerating expansion of the universe.

Sincere regards, Mike Stewart


Actually, no. Matter and energy are equivalent, and current thinking about the early stage of the universe has energy forming into matter, and matter forming into stars and galaxies. Atoms can change in number, but they do not “disappear” in the sense that nothing replaces them. The total energy, with the equivalent energy of matter, stays the same, as far as we know. The fixed sum of energy is called, “conservation of energy,” and it appears to be fundamental, i.e., no one has observed galaxies appearing out of nothing. That being said, we do not know where the universe “came from”: Did it appear (along with space and time) from nothing in a big bang about 14 billion year ago? Did the energy (and matter) exist before? Does it even make sense to think of “before time existed”? These are the big questions that still have no definite answer. In short, the total number of atoms in the universe can (and does) change, but the total energy does not, as far as we know.

Kyle Bunch

In fusion reactions, two atomic nuclei combine to make one large nucleus. When two atoms become just one atom, the total number of atoms decreases.

Richard E. Barrans Jr., Ph.D., M.Ed. Department of Physics and Astronomy University of Wyoming

No, the number of atoms is not fixed. For example, nuclear reactions (such as in the sun) involve combining atoms.

Hope this helps, Burr Zimmerman

Hi Nigel,

No. But we should still be very excited! We have nuclear reactions, changing the number of atoms for every star out there and plenty of gas all through space.

Further, we are not able to account for the vast majority of mass and energy out there: the "Dark Energy/Mass". It is difficult to comprehend what we do not know about this mysterious "Dark" phenomenon at present. We are just now learning how to predict where it is by exclusion and special spectroscopic techniques. This is incredibly exciting study.

For the present, it is uncertain how many elementary particles are out there!

Peter E. Hughes, Ph.D. Milford, NH

Click here to return to the Physics Archives

NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.

For assistance with NEWTON contact a System Operator (, or at Argonne's Educational Programs

Educational Programs
Building 360
9700 S. Cass Ave.
Argonne, Illinois
60439-4845, USA
Update: June 2012
Weclome To Newton

Argonne National Laboratory