If you don’t know someone’s age, over time they may let out clues that tell you when they were born based on what they remember, or things they claim to have done. This can be very inaccurate. My wife said something the other day that would cause anyone to infer that she was at least ten years older than she is, but it turns out the TV show she was referring to came to her home as syndicated re-runs. (My own personal memory of the recently deceased Soupy Sales is a similar example.)
You can always ask a person his or her age, but you have to infer the age of inanimate objects like The Universe. You can use radiometric dating to find the age of a lot of rocks on Earth. Maybe there are meteors on Earth that are older. Maybe there are rocks on the Moon that are older. You can then put together the ages of the oldest rocks that you can lay your hands (and instruments) on and combine that with a theory about how the Earth and the other planets formed. This would provide a minimum estimate for the age of The Universe, providing that The Universe is older than our solar system.
Which it is.
Then, if you have a theory about how the visible universe formed and a few more facts you can provide a more accurate estimate of the age of the universe. As you probably know, that gets tricky because of “expansion.” Well, it is said to be tricky, but really it is quite simple. Think, temporarily, as “distance” as a thing (Which it is, though the properties we would naturally attribute to the thing labeled by the English word “distance” do not exhaustively describe a whole thing … distance is an aspect of spacetime. But let’s set that aside here.) So expansion is this: Distance is this thing that during the history of The Universe has gotten larger. It continues to get larger, but it probably got larger really fast at some earlier time. Since light is moving along this “distance” thing, the actual (final) distance the light went is farther than it could have been at maximum speed without expansion happening. Light, which goes as fast as something can go and is the only thing that goes that fast, went faster than itself because it cheated. Much like Rosie Ruiz.
Assuming that we know the numbers, it is possible, given a “big bang” and few parameters, to estimate the age of the universe more accurately than you can estimate the age of a horse or a person using only physical evidence such as tooth wear or claims about what television show a person watched while still a kid. But it is still an estimate, not as well confirmed as if you had a birth certificate, and subject to minor perturbations depending on the exact numbers that are used to make the estimate So, additional empirical data are nice to have, and such data usually comes in the form of a galaxy or a nova (exploding star) that is really far away in spacetime.
So let’s say you know a person, and can’t figure out if she’s in her 30s or 40s. If she blurts out a knowing reference to the TV show “Edge of Darkness” then you would guess 30s. If she makes a knowing reference to Survivors, you’d guess 40s. Oh, and you’d guess her origin to be British.
Or there were reruns.
Every once in a while The Universe blurts out a reference to something that suggests its age, and that happened recently. As recently reported in Nature, astronomers have observed a gamma ray burst from a dying star and dated this event to 13.1 billion light years away. Previously, the earliest direct empirical clue to the age of the universe was 12.9 billion light years away.
From the abstract of the paper:
Long-duration gamma-ray bursts (GRBs) are thought to result from the explosions of certain massive stars, and some are bright enough that they should be observable out to redshifts of z > 20 using current technology. Hitherto, the highest redshift measured for any object was z = 6.96, for a Lyman-alpha emitting galaxy. Here we report that GRB 090423 lies at a redshift of z approximately 8.2, implying that massive stars were being produced and dying as GRBs approx630 Myr after the Big Bang. The burst also pinpoints the location of its host galaxy.
The red shift is how speed relative to us is measured, and in an expanding universe model (i.e., a Big Bang model …. the cosmological phenomenon, not the hit TV series) that speed is higher for objects farther away.
So next time you look at a person and are wondering how old he or she is, glance up at the sky (which is where The Universe is) and know that you’re never going to guess the answer to your unspoken question as accurately as astronomers will know the answer to the ultimate age-old question. Unless, of course, The Universe has something equivalent to re-runs.
Which it doesn’t.
For a refresher on the history of The Universe watch this video:
Tanvir, N., Fox, D., Levan, A., Berger, E., Wiersema, K., Fynbo, J., Cucchiara, A., Krühler, T., Gehrels, N., Bloom, J., Greiner, J., Evans, P., Rol, E., Olivares, F., Hjorth, J., Jakobsson, P., Farihi, J., Willingale, R., Starling, R., Cenko, S., Perley, D., Maund, J., Duke, J., Wijers, R., Adamson, A., Allan, A., Bremer, M., Burrows, D., Castro-Tirado, A., Cavanagh, B., de Ugarte Postigo, A., Dopita, M., Fatkhullin, T., Fruchter, A., Foley, R., Gorosabel, J., Kennea, J., Kerr, T., Klose, S., Krimm, H., Komarova, V., Kulkarni, S., Moskvitin, A., Mundell, C., Naylor, T., Page, K., Penprase, B., Perri, M., Podsiadlowski, P., Roth, K., Rutledge, R., Sakamoto, T., Schady, P., Schmidt, B., Soderberg, A., Sollerman, J., Stephens, A., Stratta, G., Ukwatta, T., Watson, D., Westra, E., Wold, T., & Wolf, C. (2009). A γ-ray burst at a redshift of z ≈ 8.2 Nature, 461 (7268), 1254-1257 DOI: 10.1038/nature08459