I asked this question in another thread re time. No one answered it. Probably because it’s such a dumb question. But from reading the GQ here, I’ve come to the conclusion that there is no question that’s too dumb to start a thread.
We measure time by the movement of celestial objects. One Earth rotation we call a day. One Moon revolution around Earth takes 28 days. One Earth revolution around the Sun takes ca. 365 of them thar days, which we call a year. Etc. We can use other heavenly bodies and have other time systems. But, as far as I can see, our measurements of time is based on motions of celestial bodies.
Astronomers say that the Universe is 15 billion years old, give or take a billion here or there, and it took 300,000 years before the ionic plasma condensed into particles and made things visible in the Universe. No life was around to notice any motions, but once the Universe condensed, heavenly bodies appeared and motion was evident. Now, in the first place, there was no Solar System to measure an Earth year by. In the second place, the whole universe was just a smear of ionic plasma at the beginning. So how can these guys say it took 300,000 years before the Universe became visible. On what basis are they measuring these years?
A year is a unit of time, independent of the orbital motion of the earth. The statement “300 thousand years” does not mean “A time during which the Earth completed 300 000 orbits”, but rather “a time equal to the period of the earth’s rotation multiplied by a factor of 300 000”.
So, it doesn’t matter if the earth was around to rotate. We just use years because it’s a convenient period that we can relate to.
Before the Universe became transparent, there was no cesium to vibrate.
I understand that an Earth year is a convenient marker. But “a time equal to a period of the Earth’s rotation multiplied”, etc. implies that time existed before transparency. I have a hard time grasping the concept of how there can time elapse when the Universe is one ionic plasma. Time must go on, I suppose, but how could we have any awareness of the march of time? In hindsight, now that we are here, we say x number of years passed and the Universe condensed. How can we make that statement? On what basis do astronomers know the years the Universe existed before it was observable, if any being were around to observe it? We say that it is 15 billion years old, and I suppose the data is there to support that. The background radiation corroborates the Expanding Universe theory and is consistent with such measurements.
It must have something to do with thoretical physics concerning ions and how they react to come to the number of 300,000 years. I’m just hazy about it.
Well, then count the average vibrations of alpha particles, or the number of gravity waves going by per second, or whatever. Even in the early plasma-filled universe there was still cause and effect: particles were still flying around bounding off one another, photons were being absorbed and emitted, nuclei were being created and destroyed, etc. If these kinds of cause and effect chains were occuring, there must have been a medium of time to do it in. Time is an integral part of the universe. They are inseperable.
IANAPhysicist, but I believe the 300,000 year figure comes from theory. That is about the time the infant universe would have expanded to an extent (and the temperature subsequently would have dropped enough) for neutral atoms to form. I don’t believe this figure is incredibly concrete, or that it stems from direct observation. Hopefully Chronos or DrMatrix will be along shortly to clear up anything I’ve confused.
When they say the universe became transparent, what they are really saying is that the universe became transparent at a certain density. Since we know the rate of expansion right now, we know the universe’s current density, and if we take into account all the things that can change the expansion rate (gravity, inflation, possibly some other factors) we can say how dense the universe was at any point in the past.
This is not relative to the thread, but it is my understanding that before the Universe became transparent there were no nuclei, as there were no atoms. It is my understanding that the transparency was the (ahem) time that the ionic plasma condensed into atoms of hydrogen and, shortly thereafter, helium. All the other elements were created later, either by solar fusion or supernovas, etc.
It depends on how soon after the big bang you’re talking about. “Nuclei” just before transparancy began would likely be just naked hydrogen nuclei. I.e., just bare protons. Not sure if any slightly heavier nuclei like deuterium or lithium were around yet. Have to wait till Chronos shows up. Also, stray neutrons would be zinging about. Earlier, even these particles would not have been together yet. The universe would just have been filled with quarks, electrons, and photons. However, they’d still be flying around interacting with each other in a before-after cause-effect kind of way.
Essentially all of the hydrogen, deuterium, helium-3, and lithium atoms now in existence, and a good bit of the helium-4, are primordial, meaning that they were made in the Big Bang. There were nuclei long before the Surface of Last Scattering (when the Universe became transparent); what happened at that point was that the nuclei started associating with electrons to form complete atoms.
Right back to the beginning, there’s always been something going on by which time could be measured. If nothing else, there’s always the Planck units, which are dependent on fundamental constants of the Universe.
read your OP from and I’ll answer your question this way.
When a scientist wants to know how long it took from t=o till a certain important event occured after that. He assigns t=x, plugs in all the other data and solves for x. That’s how they know that the end of Electroweak Unification occured at just about 10[sup]-12[/sup]s, can’t find the exact time they give. Not very satisfying is it?
Unfortunately we are stuck here on earth and as such we can only makes vague stabs at certain things. Somebody mentioned that at one point the universe looked younger then some of its stars. This wasn’t really a paradox, it just looked like one. Somebody’s measurements were just plain off. If I recall correctly I think they worked it out that the distances to the stars were off, hence the ages given to them were off.
Hopefully that new supercollider that they jsut finished and are working on getting on line will help us understand the subatomic particles better. And once we get that maybe we can finally get a Grand Unified Theory, and once we get that then our predictions at when things happened in the opaque universe will be even more precise.
What it means is that if the second didn’t exist that a second of time could still progress because time is independent of any system of measurement.
Time is really just a continuum in which events happen in succession from the past through the present to the future.
It is possible to measure time by using a reliable sequence of events that happens in a precise period of time. You can then use this ‘unit’ of time to compare other durations such as how long the universe has existed.
If you have read this and still don’t understand then you need to seek medical attention.
Also, stray neutrons would be zinging about. Earlier, even these particles would not have been together yet. The universe would just have been filled with quarks, electrons, and photons. However, they’d still be flying around interacting with each other in a before-after cause-effect kind of way.