1. Universe is really young?

Yah you are probably gonna laugh at me now. "around 13.7 billion years is young???", but I mean... compared to the age of earth. If earth is about 4.54 bil. years old, then 13.7 billion doesn't sound much... It feels like earth must be one of the very few (or only?) lucky planets to develop life so "fast". I thought it would take billions of years for the galaxies, solar systems... and our sun to form etc.

Is this "13.7 billion" (in the light of new research take or give 2 bil years) somehow a way longer period of time in space because AFAIK time functions in some crazy ways in space? I haven't studied much of physics, so I would be glad if some of you science nerds you could explain this a bit more.

2. Re: Universe is really young?

Remember it took about a billion to two billion years for life to form on earth after earth formed.

3. Re: Universe is really young?

And it did. According to the numbers you quote, it took about 9 billion years before the Earth formed.

Time doesn't behave any differently in space (except in black holes, I guess). Things do look odd when you are looking very far away or at objects moving very fast, but that doesn't mean the universe has done 50 billion years of developing in what seems to us to be "only" 13 billion.

4. Re: Universe is really young?

I'm going to assume you mean relativity. It's not so much as "in space" where time gets a bit weird, rather when you're moving really really fast. Even speeds as fast as 10% of the speed of light (30,000,000 m/s) barely cause time to get weird.

When something is moving at that sort of speed, you get what is called time dilation. This means that time actually passes at a "slower" rate for the object (well, generally it's only single particles that can get to these speeds for now). I mentioned 10% of the speed of light before, well, you can calculate how much time is affected by using
T= t/[sqrt(1-(v/c)^2)]
Where T is the time passing in what is called a "reference frame", say , a person standing on the earth, compared to the time, t passing for a particle moving at speed v, and c being the speed of light.

So if something moves at 10% of the speed of light, for every 1.005 seconds on earth, 1 second passes for the particle. Not that great right? But if particles move much closer to the speed of light (which does happen, in fact, intially after the big bang, everything was moving near the speed of light), lets say 99%. Then for every 7 seconds on the earth, only one passes for the particle.

We also know for sure this happens, because we can detect certain particles coming from astronomical events that release particles called muons, which have VERY short lifetimes (like, less than a billionth of a second), yet they arrive at the earth from outer space!

5. Re: Universe is really young?

Pardon my layman's understanding of time, Lozmaster. Totally going out on a limb here.

Doesn't time also get weird around gravitational forces? So you'd have to not only account for the speed of light at the big bang but also the massive amount of gravitational pull thus amplifying time further?

6. Re: Universe is really young?

It tends to get all Wibbly Wobbly.

7. Re: Universe is really young?

I think so, but before I continue this, I should probably mention that I've never taken an astronomy class so anything I know about astronomy is pretty limited, and the following could be completely wrong.

Basically, there are two types of relativity. One, we call special relativity, which is when you ONLY consider the effects of time dilation "far" from any mass.
The other is general relativity, where the effects of both high velocities and masses are taken in to account.

But the effects due to gravitational forces tend to be incredibly small, even compared to velocity effects.

A couple of the important things that we can work out from this are that if we were observing an object falling in to a black hole from on the earth, it would take an "infinite" amount of time for the object circling a (near) infinite mass (i.e. a black hole) to fall in to the event horizon at the centre, from our perspective. But from the perspective of the object, they would see a normal passage of time for their fall, yet the universe would age infinitely faster from that objects perspective

It also describes how much time is shifted by for masses that aren't so large, but G is very small (10^-11) and then dividing by the radius from the mass*c^2 ~10^-17 smaller, so very large masses are needed before it really comes in to play.

That is not to say it's negligible on Earth. Suppose the international space station orbits at about 350km (if google doesn't lie to me) and the Earth has a mass of 6*10^24 Kg. Quickly checking the above formula means that there would only be a 1*10^-9 second delay between a clock on the ISS (Well, that's assuming all of Earths mass is at it's centre, but it is a good estimate). This could probably cause problems with GPS locators and other things that send information between the earth and the satellites, but I assume someone somewhere has done some math to make corrections for these.

But yes, saying the effects are always small is a bit of a lie, given that it becomes more relevant when you have a black hole in space, as you mentioned, because they have essentially an "infinite" density. It isn't infinite, but as far as I know, there is no experimental method that has currently been invented to measure the mass of a black hole.

In fact, it's probably all the relativistic effects that are preventing people from measuring the mass of black holes. I know you can work out the mass of a regular planet or star judging from how other astral bodies travel around them, using Keplers laws and Newtons gravitational law, through very accurate measurements of the positions of the orbiting bodies, but these laws don't apply to measurements of objects close to large masses, like black holes.

tldr: Relativity is crazy.

Edit: Waiiiiiiiiiiiiiiiiiiitttttttttt. That formula is insane! What would happen if 2GM/rc^2 is bigger than 1 (i.e., M/r> c^2/2*G=1.35x10^27)

Ok, thats a large number, and only still important near the very centres of either incredibly dense masses or black holes, but the result would be an imaginary number, which is as far as I'm aware ridiculous. (Because time isn't an imaginary quantity...)

And only a weekend left before lectures start again, well looks like I have some researching to do tomorrow. (I sure know how to have fun weekends!)

8. Re: Universe is really young?

With our a priori knowledge (life exists here and now) it's hard to gauge the probability of this event's occurence in general. Obviously here and now it is 1.

4.5 billion years is a long time by human standards... our species has only existed for maybe one ten-millionth of that time. When you're talking evolution, punctuated equilibria is what dictates progress - it could stay stable for a long time, or the correct mutations & events could make it happen quickly. It takes a while for abiogenesis because everything's random chance, but once evolutionary factors kick in, for the most part, progress is maintained - it's more likely to advance than to regress.

@ abvoe I'd have to look in more detail but I believe the 'event horizon' of a black hole is the radius where the speed of light is exceeded and nothing can escape. Mass has to be quite dense for this to happen.

And yes, the relativistic time difference is taken into account with satellites.

9. Re: Universe is really young?

Duration is subjective, and depends on the perspective of the observer.

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