Hi, I'm new here. I posted this question to Sciam but never got an answer, so maybe you can enlighten me.
It is said that the age of the universe is somewhere between 13.5 to 15 billion years old. I guess they came to this conclusion observing the actual rate of expansion of the universe and then extrapolating by calculating back in time for a singular point of origin (the famous big bang event), it is kinda playing the tape in reverse 'till you get back to the beginning. However, how do we know that time itself has been linear ever since the big bang?
According to Einstein, time is also gravity dependant, so it makes sense to think that neither time nor the rate of expansion of the universe hasn't always been constant. So to speak, universe and us could've well been born yesterday and we just don't have a way of knowing it!!!

Dan

Generally speaking, in general relativity, there are two kinds of time: coordinate time and proper time. The former is the one that is gravity dependent, but the latter is not. When scientists report a calculated age for the universe, it is always a proper time, and therefore independent from gravity. However, a cosmology is just a model for the universe that includes general relativity as the theory of spacetime. The age of the universe is very much dependent on the details of the model, and cannot be derived purely from observation.

In most cases the age is arrived at in much the way you suggest, by using measured values of the Hubble constant to get the "expansion age" of the universe (see, i.e., "How Old is the Universe?). But we can also use more "ordinary" astrophysics to derive ages for stars. We then assume that the age of the oldest stars must be a minimum age for the universe, since it cannot be younger than the stars that are in it. 13 to 15 billion years is a good range, consistent with most cosmologies, and not mtoo outlandish.

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The point of philosophy is to start with something so simple as not to seem worth stating, and to end with something so paradoxical that no one will believe it. -- Bertrand Russell

Why is it that physicists, whatever their apparent "cleverness", simply CAN NOT explain something in simple language?

"Coordinate time"?

"Proper time"?

HOW does one come by these concepts? Can they be explained WITHOUT convoluted advanced mathematics?

I agree that science should be backed up with the hardcore maths. However, when a scientist fails to EXPLAIN in CLEAR LANGUAGE a scientific "idea", I (and I'm sure most of us) lose interest.

Is "reality" so esoteric that it is owned by the elitist intelligentsia, and nobody else?

Surely if we cannot DESCRIBE this universe is clear language, but resort to convoluted nonsense like "coordinate time" and "proper time" (and whatever other versions of "time" there is out there in scholarly land), then SURELY the reasoning is wrong/misguided/false.

Spit it out in clear language, please. Not ambiguous sloganeering.

I completely understand that you'd need a special vocabulary to describe certain scientific concepts. You need a special vocabulary in any field. Maybe it's just me, but I assume that, if you're really interested in the subject, learning a few words isn't that much of a challenge.

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Gillian

"Now everyone was giving her that kind of look UFOlogists get when they suddenly say, 'Hey, if you shade your eyes you can see it is just a flock of geese after all.'"

"You can't erase icing."

"I can't believe it doesn't work! I found it on the internet, man!"

Explaining what "proper time" and "coordinate time" would require
several thousand words, and a significant effort on the part of not
only the writer, but the reader as well. However, the concepts
of "proper time" and "coordinate time" are at the foundation of
special relativity, so any book which explains special relativity from
the beginning will explain those terms.

There are hundreds of such books, but I'll suggest "Relativity: The
Special and the General Theory" (English translation 1961) by Albert
Einstein, and "Spacetime Physics" (1992) by Taylor and Wheeler.
If you don't care for either of those, you can find another that will
be more to your liking.

"There is no royal road to geometry."

-- Jeff, in Minneapolis

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http://www.FreeMars.org/jeff/

"I find astronomy very interesting, but I wouldn't if I thought we
were just going to sit here and look." -- "Van Rijn"

"The other planets? Well, they just happen to be there, but the
point of rockets is to explore them!" -- Kai Yeves

There is a story that a journalist in the U.S. wired Einstein asking for an explanation of relativity in a thousand words or less. The reply was around 18,000 words! Physicists in the U.S. told the journalist that that was about as succinct as you could get!

Pick a field (any field) of study. It will, by necessity, have developed its own language (jargon, if you will). It simply cannot be helped.

I read Scientific American regularly. In articles outside of physics and astronomy, I often find that although all the words are in English, they make no sense to me at all. A specific example: My brother picked up a copy of SciAm that had an article about colliding gold nuclei in an "atom smasher". He gave it to me because the article was way over his head (he is very intelligent and well educated, but not in this field). I understood the article, but the one about RNA transcription was pure gibberish to me.

Besides amateur astronomy, I am also interested in live sound reinforcement and music recording. I can recall, on many occasions, getting in to conversations with other sound people that left even professional musicians thinking we were speaking a foreign language.

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Any day you wake up on "the right side of the dirt" is a good day.

T. Anderson

There's definitely a kind of glass ceiling with physics where the metaphors and simple explanations don't really explain that much, and you just plain have to do complex math if you want to understand it in any more detail.

I know I'm certainly in the "metaphors and simple explanations" class, but I'm thinking about getting back into math to see what more I could learn about this stuff.

SillyMidOff, how about explaining the rules of cricket in simple, clear English ... preferably 100 words or less?!

As others have already mentioned, it's not just in physics that you need specialist terminology - pick any area of "reality" and try explaining it in a manner that meets your criteria.

One of my favourites is the computer+internet that we use to communicate with each other - I mean, what could more simple than I type words, you type words, and we can read what we each write?

Or, if you prefer something of a more life-and-death nature, how about explaining AIDS (and its treatment and why it can't be cured) simply? or cancer (ditto re treatment and cure)? or why we can't live to be 1,000 years' old?

Hi you SOULS (!!!),
this is truely my first computercontact with life out there!

Since this is EVERYbody's universe , you should insist upon that it may be explaint to you in terms that you understand. And to quote Einstein for a second time (in this thread), he marveled alout about the "strangeness", that the universe makes itself understood to us (or be it at least to a astounding degree). It is sofor a lamentabel thing, that the questions of interest to the professional sientific comunity are often of such an arcane nature as to preclude all interested lay bystanders from any meaningfull participation.
Questions as to the absolut definitif meanig concerning the overall age of the universe or the validety of the time concept "at the beginning of time" in the context of an inflationary expanding space under considerration of ... blabla can only bedoudle the inocent. Ok, if you have had a very confined (say) christian upbringing, you may want to expose yourself to a good helping of strangeness, to shatter a certain narrowness of mind. And you can get it from cosmology , astrophysics etc.....But if you look for a sense of understanding , you should stick to concepts, that are inate to our (very ,very highly developed) commun sense. The traditional feel of space and time (without even special relativety) carries one a good far. One is very ill advised indeed, if one lays to great a weight on the validity of the most reecent findings in pondering the nature of nature...
To me personaly, the most significant thing about the universe is ...............that it is r e a l l y, r e a l l y B I G and old!
Hey it is not far in the past, that the world was 6000 plus years old and very, very single. So we have come far eaven with a trivial perspective to the thousend upon thousend wonders in the celestial spheres. Also can we with great calm wait for the last riddels to be unriddeled and be straightend out befor our eyes of a once hopefully eaven more enlightened human race... ^ ^ ...
(plesase don't take offence to the twisted style of a foreigner. good day)

Welcome to the board, satori.
No offense taken. You make more sense than some native speakers here.

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Any day you wake up on "the right side of the dirt" is a good day.

T. Anderson

But are physicists allowed to insist that the listener have a certain level of education in order to understand? Or at least insist that the listener have the patience in case the explanation is more than 1000 words?

Is there any such thing as a polymath these days?

I see this as a fundmental problem within Science, and without.

"Knowledge," as it were, is so compartmentalized that noone really knows or understands what everyone else is talking about!




But as for the OP, no, I don't think the alleged age of the universe is accurate.

This, of course, comes from someone who studied English and Sociology.

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"Where the telescope ends, the microscope begins. Which of the two has the greater view?" - Hugo

"Men occasionally stumble over the truth, but most pick themselves up and hurry off as if nothing had happened." - Churchill

I do, and I studied English, history, and music. However, I defer judgement to people who study science--if it's good enough for the more knowledgeable, it's good enough for me!

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Gillian

"Now everyone was giving her that kind of look UFOlogists get when they suddenly say, 'Hey, if you shade your eyes you can see it is just a flock of geese after all.'"

"You can't erase icing."

"I can't believe it doesn't work! I found it on the internet, man!"

The very nature of science is what saves it from fundamentalist extremist belief. Science is willing and eager to throw aside all previously held perceptions on the arrival of new scientific fact. As to how many letters you have after your name or what doctorate you might have acquired carries little weight with me. It is what you are saying now that I will judge not what you may have said. The quest for knowledge is relentless. The constant search for new information will not stop just because I have drown a conclusion. Nor should it.

The age of the universe. . .?
With the most sensitive and massive of radio astronomical equipment we seem to have arrived at the background radiation as a remnant of the Big Bang. 13.7 billion light years away, or is that ago...?
Regardless of the fact of massive expansion at ever increasing velocity make all of this a little bit tricky. Can I draw the conclusion that this universe might be 27.4 billion light years across. No, thats bound to be wrong for reasons that will be obvious to all but me.

Well, you have a point. But to communicate anything, one does have to assume some background to the conversation....

One way to think of the background to a conversation is by comparing a conversation to two people building a wall. The building skills and experience the two individuals bring to the task are part of the background. So too is the supply company that delivers the bricks, sand, and cement. All of these contribute to the building of the wall, and some of them are essential to the task. But none are part of the actual building work. The one part of the background that can be regarded as part of the actual building process is the preparation of the foundations for the wall, since the foundations are, in a sense, part of the wall. The construction of the wall then proceeds in a step-by-step fashion, as the two persons add one brick after another in a coordinated and cooperative fashion... each new brick builds upon those that have been laid previously. The attention of the two people building the wall is focused entirely on the wall and its foundations, not on anything in the background. -- Keith Devlin, author of Goodbye, Descartes

When the participants don't have a lot of background in common, you might run into the following sorts of problems:

"Recently at a New York cocktail party, a young physicist was asked how he made his living and he replied that he was by specialty a cosmologist. While it might be debated whether cosmology constitutes a "living," his host remained undeterred and immediately inquired if it would be possible to make an appointment for a manicure and a haircut." -- Tony Rothman, author of Science a la Mode, Physical Fashions and Fictions [1989]

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Everyone is entitled to his own opinion, but not his own facts.

I do not intend this an attack of any sort on the poster who posted it, but I do take issue that "the universe belongs to all of us". The universe doesn't "belong" to anyone. If there's any ownership there, I'd say the universe owns us. It made us, it can take us away. Any darn time it
pleases. Poof goes this little dust speck in some galactic scale energy hiccup that to us would be of enormous proportion, but is nothing but flatulence in a hurricane to the universe.

And second, there isn't any right to know anything. We all have a right to use our own faculties to try to learn the "secrets of the universe", but don't have any right to demand anyone else give us their knowledge in some fashion we demand.

There is no "simple language" to explain things sometimes. If you want to understand, you've got to do some work. If someone with more knowledge is nice enough to try to explain things, well, take it for what it is, a gift. Don't look gift horses in the mouth.

-Richard

Well,

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well, i don't know much about the two systems of time but I would have thought that time within the early Universe would have nothing else to be relative to. Like time for mercury is different than time for people on Earth, due to the gravity of the Sun. But there would be nothing like that differency in distance in the early Universe, even if there was a lot of mass and gravity about.

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Why is it that when someone asks a question that they don't have sufficient background to understand the answer to, they get upset and blame the person who answers?

I don't think the sarcasm and outright rudeness ("apparent 'cleverness'"? You haven't taken the time to even look into what the phrases might mean, and you're mocking people? Get real!) is called for. You'll catch more flies with honey, after all.

"Coordinate time"?

"Proper time"?[/quote]

Coordinate time is time that depends on what set of coordinates you use to measure. Proper time is time that is independent of which coordinates you use to measure.[/quote]

It's simple calculus. Why do you consider it to be convoluted? It's downright straight forward if you know the mathematic principles starting out. It's only "convoluted" when someone who doesn't bother to take the time to understand it passes it off as unimportant.

The concept was explained in easy to understand language. Tim threw in a couple of technical terms (Coordinate and Proper times), but they were merely bonus material. You can replace the phrase "coordinate time" with "time affected by gravity" and "proper time" with "time not affected by gravity" and the answer comes out the same: Cosmologists report the age of the universe using the gravity independent time.

It seems to me like you want simple answer to complicated questions. I suggest grade school. The kind where they explain the northern lights as "light reflected off of glaciers".

No, but it is so complex that if you want to understand it, you'd best be prepared to work for it. If you want easy, pretty, or made up answers, there are plenty of websites offering them. Usually at a hefty sticker price. Here, there's a community of people ranging from the curious to the over-educated, most of whom are patient and willing to do what it takes to learn or explain. If the answer isn't clear the first time through, people are nice enough to sit down with you and try to explain it in a different way until you catch on, so long as you're willing to try to catch on in the first place.

You may as well walk into the IRS and ask how all of your tax dollars are being spent, while demanding the phrase their answer in a hand gesture.

"If I can't understand it, clearly it's wrong." Sorry, it doesn't fly. You pretty much want someone to explain the workings of the entire universe in language a 4 year old could comprehend. You can't even explain the workings of a dishwasher like that. "Plates come out clean" just doesn't cut it in the real world.

Sure.

We have these machines called "clocks". They're used to measure the passing of "time".

With me so far? Good.

When I look at other peoples clocks, how quickly I see their clocks count time depends on where they are. When I look at someone who is moving away from me, I see their clock running slower than mine. I also see their clock running slower than mine when they move toward me, or when they're on the floor below me. However, when I look at someone on a floor above me, I see their clock running faster than mine. Because I see peoples clocks working at different speeds depending on where they are, I'm not going to measure the age of the "universe" using their clocks.

I always see my clock run at the same rate, though. It doesn't matter if I'm at the top of a mountain, or deep under the sea. It ticks away steadily whether I'm moving quickly, or standing still. It doesn't depend on speed or location, so I'm going to measure the age of the universe using my clock.

Is that clear enough, or should I break it down every further?

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"The plan does not involve mayonaise."
"... I knew there was a catch."

You can't take the sky from me.

Hi. I just don't get it, with or without proper time. The thing is that since we live inside of this universe, we just don't have a way to know whether the clock is ticking faster or slower. There is no absolute time for us whatsoever. Processes (like the expansion of the universe or the stars formation or clocks ticking) could be happening slower now than before or the other way around and, if you are inside, how could you tell the difference? or put it in other words, how to tell if universal constants (like Hubble's) are or have been really so? Can anybody explain in "proper english"? TKS, Dan

That statement does not really make much sense when coordinate time is nothing more that what proper time would be for an observer at that point. The concept of coordinate time is usefull for speaking about proper times across the entire coordinate system rather than for particular observers. It is not a different "kind of time" or coordinate system. It is not possible to speak of GR being independent of proper time when proper time changes as the depth of field changes and coordinate time is the proper time on the whole coordinate system.

Who's upset? I'm not upset.

Yo, if you object to what you perceive as "sarcasm" and "outright rudeness" in my post, don't you think it ironic to use the same measures back at me? LOL...!

That's right, I'm no mathematician. 3-year B.A., but no formal maths training. Sorry! I suppose that disqualifies me from your special club.

Still gobbledy-gook, I'm afraid!

Not necessarily "simple" answers, but answers in layman's terms. No maths, no esoteric buzzwords. Just plain language. C'mon, Hawking, Davies, Greene, et al, can do it!

BTW what grade school did you go to?

That's why I'm here!

A hand gesture is what I would expect from them!

Reading between the lines of this rather hysterical quote of yours, Kristophe, I sense that you believe that you DO in fact understand "the workings of the entire universe", but couldn't possibly even BEGIN to explain it to a common peasant like myself?

Nope, that's fine thanks. And after a rather long-winded & emotional preamble, you finally deliver the goods! Thanks! That was all I was asking.

Thanks to the finite speed of light, we see far off things as they were billions of years ago. If, for example, the force of gravity was slowly getting weaker, we would see pulsars that are orbiting companion stars to be moving outward in their orbits. Pulsars can be timed very precisely, and this change in orbit is not observed. The universal gravitational constant appears to be quite constant. Most of the other constants can likewise be cleverly determined to have varied hardly at all (if at all) in the history of the universe. For example, look up the Oklo uranium mine in Gabon, West Africa, and the relative abundance of samarium at that natural nuclear reactor site that "went critical" about 2 billion years ago....

Well, I don't think Hubble's "constant" should really be considered a "natural" constant like the masses of protons and electrons or the strengths of electrical and nuclear forces. Besides, Hubble's "constant" is probably better referred to as "the Hubble parameter" since it is a value that is time dependent. It appears that the expansion was initially slowing - due to the gravitational effect of all the mass in the universe - and later it slowly started to accelerate - due to some "dark energy" quality of the "vacuum" of space.

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Everyone is entitled to his own opinion, but not his own facts.