Guide to the Cosmos
Making the Wonders of our Universe

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Robert L. Piccioni, Ph.D.

Journey to the Dark Side:
Dark Matter & Dark Energy


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Dark Matter is revealed as it bends light.

Normal matter has only 4.5% of the total energy in our universe; Dark Matter (“DM”) amounts to 22.5%. DM doesn’t emit or absorb light, but we detect it as its enormous gravity bends the light from more distant stars and galaxies. The degree of light bending tells us where and now much DM is present, shown in purple.

The “Bullet Cluster” shows the aftermath of a collision of two galaxy clusters that are circled in the image. The purple Dark Matter (“DM”) appears unaffected by its passage through galaxies, ionized gas (plasma shown in pink), and even other DM.

The collision of 2 galaxy clusters shows dark matter is unaffected.

Dark energy is accelerating the expansion of the universe.

Since all galaxies gravitationally pull on one another, the expansion rate should slow down over time. Indeed, these data show the rate was higher long ago (to the right) and dropped to a minimum 6 billion years ago. However, the rate has increased; the expansion is now accelerating. This surprise is attributed to Dark Energy.

Dark Energy is most likely the effect of virtual particles predicted by Quantum Mechanics. If so, space has positive energy and negative pressure, leading to negative gravity — it pushes everything apart. When the universe began (left side), the amount of space was small and the attractive gravity of matter dominated. As space expanded, the density of matter dropped.

in the beginning, energy density of matter dominated gravity. But now, energy density of space dominates.