Q: When I read that “the universe is 13.7 billion years old,” I wonder: Don’t scientists use some more universal measurement than years, something not tied to the orbit of one tiny planet?

Modern measurement of time builds on the second, based on atomic oscillation, rather than on the variable time it takes the Earth to orbit the sun.

As the National Institute of Standards and Technology explains, a second has been defined since 1967 as the time it takes for a cesium atom to oscillate 9,192,631,770 times between two radiation states.

An alternative unit called the cosmic year has been suggested, based on the sun’s orbit around the center of the Milky Way galaxy about once every 225 million years.

But this “year” is not routinely used by cosmologists, said Andrew Hamilton, a professor of astrophysics at the University of Colorado.

“The age of the universe is not something that is directly measured by astronomers,” Hamilton said. “What they measure is the rate of expansion of the universe, as measured by the so-called Hubble parameter” – named for the 20th-century astronomer Edwin Hubble, who was one of the earliest to calculate the expansion rate by noticing that the more distant galaxies are receding at faster speeds.

A value called the reciprocal of the Hubble parameter is approximately equal to the age of the universe, or 13.7 billion years, he added.

“It is not exactly equal,” he added, “because the universe has been decelerating and accelerating under the influence of gravity.”

Q: Does taking a “blood thinner” make a person feel colder? Does blood thin when people move to a warm climate, making them feel colder if they move back north?

Changes in perception of heat and cold are highly individual, but “the thickness or viscosity of our blood has nothing to do with how we experience the temperature,” said Holly S. Andersen, director of education and outreach for the Perelman Heart Institute at NewYork-Presbyterian/Weill Cornell Medical Center.

A blood thinner works by slowing or impairing the blood’s ability to clot, Andersen said, and will not make someone feel colder.

Being exposed to high altitudes, where there is less oxygen, can actually make blood become a little thicker over time because the bone marrow will produce more red blood cells, which carry oxygen, she said

“In the cold, the small blood vessels on the surface of our body get smaller to keep warm blood deeper inside.”

Overall, how warm or cold a person feels “has more to do with our perception of temperature than with our actual temperature,” she said.