Age of the Universe

.The fact is that time is inextracably linked to space.This is because in order for the spatial dimensions to produce the universe they need to move through their respective planes and the process of motion is the component time.I must point out that the universe is said to have begun around 14 billion LIGHT-years ago.

You used a distance measure as it it were a time measure.I have never noticed this "said" anywhere correctly. Where did you get this from?

I have seen it used rarely myself but I do believe it is the proper form in the same way we use spacetime as a singular term.Since looking out into the universe through various means any information we obtain arrives as a spacetime component, lightyears expresses this dual nature and also boosts our understanding of the true nature of what we observe.14 billion years ago ignores the distance component.[This message has been edited by sidelined, 10-25-2003]

Sorry, Sidelinbeed, but that bit about light-years is nonsense. I don't know where you got it, but you should put it back there.A light year is a distance, 5880000000000 miles (approx). Your statement makes as much sense as saying that Christmas is 23 feet away.Your aeroplane flight is a very confusing example. The chronometer in the plane would slow down as the plane takes off and land due to inertial effects. But it would speed up while the plane is higher in the Earth's gravitational field. Clocks in satellites do run measurably faster than at earth's surface.So let me try an example which might make the situation clearer.We will send a spaceman on an 8 year trip at a speed which will give a 50% time dilatation (from our point of view). Ie. about 0.87c.
After 4 of our years, he reaches a distant planet, and turns around. At this point his clock has registered two years. He agrees with this, because for him, the distance has halved due to the Lorentz-Fitzgerald contraction.But from his point of view, our clock has only registered 1 year. This is an important point. The PRESENT for distant objects is relative to your reference frame. His idea of the 'present' in space-time is not the same as ours.Now our traveller turns about for the return journey, and this is where interesting things happen. From his point of view, he is suddenly in a gravitational field, and we are at an altitude of 2 x 0.87 light years 'above' him. He sees the same effect as we do looking at a clock in a satellite - the clock speeds up. So he sees our clock speed up, making up the difference and then going way ahead of his clock. He is now in a different reference frame, and his view of the 'present' has changed. He now sees our clock registering 7 years!As he travels home, from our point of view his clock registers another two years while ours registers 4. From his point of view, our clock advances from 7 to 8 years, while his advances from 2 to 4.
So when he arrives back at Earth, we agree that his clock registers 4 years while ours registers 8 years.All the confusions arise because the traveller changes reference frames by changing his speed, and thereby changes his view of the present. If the trtaveller keeps moving in one direction, Special Relativity can handle it with no problems. But if he is to return, he must change reference frames, and General Relativity is required to explain the situation.Please note that the time effects of his initial acceleration away from Earth, and slow down on return, are very small because he is so close to us that the difference in gravitational potential (his pereception of his acceleration) is small. Like a clock 1 foot above your head not going measurably faster, where one up in orbit does.I hope that lot helps. The best book I have read describing all this is 'The Logic of Special Relativity' by Prokhovnic.Maybe next time I'll get involved in the balloon discussion.Mike.

Is there a typo in this sentence, because this is dead wrong. Both observers see the other's clock slow down. No, I guess it wasn't a typo. As I said before, I don't know the specific details of how one clock is ahead of the other once both clocks again occupy the same reference frame, but I believe it happens during acceleration/deceleration. But when both clocks are traveling at a constant velocity relative to one another, each will see the other's clock running slower. This is because there cannot be a preferred reference frame, one which is considered stationary and one which is considered moving.You have mentioned the Lorentz transformation several times now. Perhaps it would help if we used a specific example. Let us imagine that the airplane is traveling at a constant velocity of 259,628 km/s, and that from the ground we observe its clock for 1 second by our time. We will find that only 0.5 seconds goes by on the airplane's clock (that's because the Lorentz coefficient is .5 for 259,628 km/s).Of course it is perfectly legitimate for the observer in the plane to assume he is stationary and that it is the ground that is traveling at 259,628 km/s. When he observes the clock on the ground for 1 second by his time he finds that only 0.5 seconds goes by on the ground's clock.Now, here's where my knowledge grows thin. We know that when the airplane lands that its clock will be behind the ground's clock. I cannot explain the details of how this happens, it involves general relativity which is a step up in complexity from special relativity, but I believe it is related to the accelerations and decelerations of the plane during its trip.--Percy [Correct velocity used in example. --Percy][This message has been edited by Percipient, 10-26-2003]

Hi Justin!I think you're right that there's a terminological and conceptual conundrum involved. We have neither the terminological nor conceptual tools with which to properly express such things as the beginning of time. Perhaps someone else has a better answer, but all I can say suggest is that you attempt to go with the spirit of what is meant and not worry too much about the precision of the available terminology nor the lack of an appropriate pre-existing conceptual framework.--Percy

There's an old Peanuts comic where Lucy takes her younger brother Linus out in the backyard on a clear night and tells him all kinds of misconceptions about the heavens. In the closing frame Charley Brown says, "Poor Linus, he's going to have to go to school twice as long so he can unlearn everything Lucy teaches him."I hope no one pays any attention to your tidbit about light-years.--Percy

Hi sidelined!Your cosmology is worse than Creationists like Russel Humphreys and Barry Setterfield. Time and distance have no one-to-one correspondence. Specifically, light-years and years are not equivalent.--Percy

Hi Mike,I'd like to question a couple things in your example and see if we can figure out whether they're really right or not. I think you may have actually introduced more complexity. First, the slowing of the clocks should be symmetrical. If we observe his clock as advancing two years during the outward journey, then he will also observe our clock as advancing two years during the same period. Even when you include translation effects (ie, that the light from our respective clocks takes time to reach each other) the effects are still symmetrical.Second, if he's intends to travel outbound for 4 years and then reverse direction and travel inbound for 4 years, why does he turn around after 2 years? Perhaps you intended to say that his goal was a distant planet 3.48 light-years away (4 years * 0.87c)? I wasn't able to figure out why he is suddenly in a gravitational field. Are you talking about the deceleration/acceleration that happens when he reverses direction? Suddenly just by reversing direction he sees our clock at 7 years instead of one year? I don't think so. For one thing, he is 3.48 light years away, so the time he sees on our clock hasn't even reached a year yet. The translation issue is why the airplane example is easier.--Percy

Hi all,Just thought I'd include my two cents. As I understand it the two clocks will indeed register different times (the clock in the plane running slightly behind) and therefore necessarily give different answers for the age of the universe. This is not a problem however, since they will still pinpoint the same moment as the time when the universe came into existence. If clock A registers x seconds, then the time of the BB will be x-x=0 seconds. Clock B registers y seconds, so the time of the BB will be y-y=0 seconds. They will both give the same answer for the moment when the universe was created, but disagree on how much time has passed since then. However, if they know the movements of the clocks then the difference can be reconciled.On the problem of the equality of the frames of reference the following applies. As long as both clocks travel at a constant relative speed (not zero), both will say the other clock is running slow. This apparently gives a paradox. The paradox is solved however when we take into account that to make an accurate comparison, the clocks have to be in the same frame of reference. In order for this to happen one of the clocks has to undergo an acceleration. It is precisely the acceleration that brakes the symmetry, and the frame of reference that undergoes the acceleration will be the one that will be running slow compared to the other (in this case the clock on the plane). This can be mathematically proven (it was an exercise I had to do in college).

More like a 20 dollar gold piece - thanks!--Percy

I must agree that I am in the wrong here and I apologize for running off at the mouth in areas where I have no formal background and I am determined to rid myself of the pain from this sound thrashing by making a concerted effort to study the mathematics behind relativity Perhaps I will come back to these discussions from time to time and get help straightening the curves of my knowledge.
One of the interesting things that come from this is that in order to see my error I have learned a whole pile of things concerning relativity that I did not realize before.Your humbled friend

With clocks in areoplanes the matter is complicated by some additional considerations. An aeroplane flying at altitude has clocks running more quickly than clocks in the ground due to differences in gravitation. Analysis of this effect requires general relativity, and both observers will agree on this effect. Also, the motions of an aircraft are not simply linear motions. A long aircraft flight makes a circular motion around the globe, and the Earth's rotation means it makes a difference whether you go east, or west.There was an experiment performed in 1971, in which atomic clocks were placed in transcontinental aicraft and flown around the world eastwards, and westwards.Here is a page describing the calculations and results for this Hafele and Keating Experiment.You mention accelerations. Acceleration can be handled just fine using special relativity only. You only need general relativity for gravitation; but for accelerated motions without gravitation special relativity works just fine. Here is a web page which explains the twin paradox using spacetime diagrams. Note that general relativity is not used. One twin has a change of reference frame, and that breaks the symmetry of the experience of the two twins. See: The Travelling Twins Puzzle.

Hi CJ!The effect of gravity at different altitudes has been mentioned before, but this is a thought experiment and so in the airplane example we're ignoring these effects. You could make the airplane a rocketship and the ground a spacestation, but someone could still object that you still haven't escaped the effects of gravity since both rocketship and spacestation have mass and therefore gravity, and while their influence is less than the earth's it is still finite and real. In the real world it is impossible to get rid of the influence of the rest of the universe, hence we employ thought experiments. Your twin paradox thought experiment also ignores the effects of earth's gravity. Just so other people don't get confused, let me clarify that your referenced webpage (The Travelling Twins Puzzle) is not saying that the turnaround is not an issue of general relativity. What it is actually saying is that while the turnaround is still an issue of general relativity, deriving the effects of acceleration only requires the math of special relativity by viewing the accelerated reference frame from an unaccelerated frame and integrating across the instantaneous velocities over time. Implicit in general relativity is that acceleration and gravity are indistinguishable from within the reference frame.--Percy

Dating the age of the universe has evolved since 1929 when Edwin Hubble's discovery that the universe is expanding suggested-based on his earliest measurements- that the universe was only 1.5 billion years old. Even at that time, it was in obvious contradiction with the age of the Earth, which was even then known to be several billion years old. In the 1980s, estimates of stellar ages suggested that the universe had to be at least 16-20 billion years old. The inconsistency with the Hubble age provided motivation to reintroduce the cosmological constant first proposed by Albert Einstein in 1916. However, refined estimates of stellar ages, and the age of the universe is estimated at 11.2 and 20 billion years old.Astronomers can place a lower limit to the age of the universe by studying globular clusters. Globular clusters are a dense collection of roughly a million stars. Stellar densities near the center of the globular cluster are enormous. If we lived near the center of one, there would be several hundred thousand stars closer to us than Alpha Centauri, the star nearest to the Sun.An alternative approach to estimating is the age of the universe is to measure the Hubble constant. The Hubble constant is a measure of the current expansion rate of the universe. Cosmologists use this measurement to extrapolate back to the Big Bang. This extrapolation depends on the history of the expansion rate which in turn depends on the current density of the universe and on the composition of the universe.If the universe is flat and composed mostly of matter, then the age of the universe is2/(3 Ho)
where Ho is the value of the Hubble constant.If the universe has a very low density of matter, then its extrapolated age is larger:1/Ho.
If the universe contains a form of matter similar to the cosmological constant, then the inferred age can be even larger.Many astronomers are working hard to measure the Hubble constant using a variety of different techniques. Until recently, the best estimates ranged from 65 km/sec/Megaparsec to 80 km/sec/Megaparsec, with the best value being about 72 km/sec/Megaparsec. In more familiar units, astronomers believe that 1/Ho is between 12 and 14 billion years.If we compare the two age determinations, there is a potential crisis. If the universe is flat, and dominated by ordinary or dark matter, the age of the universe as inferred from the Hubble constant would be about 9 billion years. The age of the universe would be shorter than the age of oldest stars. This contradiction implies that either 1) our measurement of the Hubble constant is incorrect, 2) the Big Bang theory is incorrect or 3) that we need a form of matter like a cosmological constant that implies an older age for a given observed expansion rate.Recent studies though has shown that the Universe is actually a dodecahedron.Whether you believe it or not we are living in a golden age of observational cosmology, where our fundamental picture of the universe has been revolutionized in the last decade. At the same time, we are establishing the essential features of the cosmos that will serve as the datum at the basis for fundamental physics in the 21st century and beyond.