# NowThatWeKnow

Senior Members

391

## Posts posted by NowThatWeKnow

### Saying thanks (reputation)

How many thanks do you have to spread around in order to give thanks to the same person again? Is there also a time limit to say thanks twice to the same person.

Some people devote a lot of time and energy to helping people with qualified answers but a month later I still can not say thanks again (Martin comes to mind here).

So, what are the rules?

### About black holes and time...

...Perhaps, If I think about the event horizon as an asymptote... matter going towards it will never reach it typically, like a divergent graph. but if the rate at which it is aproaching increases enough, the "graph" could become convergent... And there could be a point in our time as the observer at which the matter actually reaches the event horizon and then force would be exerted on it....

Come on guys i need someone to answer other than me

I am interested but do not feel qualified to add much substance to what you are saying. Wikipedia describes the event horizon and what happens as you approach it.

http://en.wikipedia.org/wiki/Black_hole#Event_horizon

It does seem to indicate an object falling into it finally does disappear by red shifting past a certain point. Other articles in Wiki describe falling into a black hole and you finally are ripped apart and become a part of the singularity. The time dilation that freezes an object at the event horizon does finally give up the image it seems.

### A Universe without Time

In the strictest sense, he is arguing for a universal time, and that time is the present... and all observers regardless of reference frame (he argues) are sharing the exact same present.

That's my interpretation, anyhow. Cheerio.

Sometimes his wording does leave his thoughts open to different interpretations but I think you are pretty close. However, if we could have a synchronized clocks at any two locations, wouldn't that show we can be sharing the same present or "now"?

### Telling universe time from the stars

To look out in space from earth set it up by putting in .27, .73, and 71 as the present matter and DE densities, and the Hubble rate. Try out different z #'s up to z = 1000

### Telling universe time from the stars

Pretend that alien in the future points his telescope at the Milky Way

and finds that it has redshift z = 2.23.

So you already put in Omega = .01

Lambda = .99

H = 60.8

So now put in z = 2.23 and press "calculate" and see what you get.

What you get is us! The alien sees us. And for us the age of the universe is approx 13.7 billion (it will get it nearly right) and for us the hubble rate is approx 71 (it will say around 70 which is close enough.)

http://www.uni.edu/morgans/ajjar/Cosmology/cosmos.html

A quick peek for those that do not want to try it for themselves.

### Shape of a light flash

...NowThatWeKnow gravitation : suppose a light beam horizontally emitted, the aequivalence principle says there is a vertical component and hence is bent (but the speed norm remains c),...

I understand the speed of light is constant in a vacuum and flat space.

### A Universe without Time

I view the difference of time in different time frames to be caused by different clock rates. The compression of length by velocity should cause an increase in density or molecular concentration which could cause a slowing of any “clock”.

I can not think of anything that could not be used as a "clock", even if the rate of decay is used to measure time. I would also use caution when comparing absolute and universal time to each other.

### A Universe without Time

...Time as I see it is the force that maintains the present i.e. “now”. I propose that it marches on or progresses at a uniform rate from the big bang constituting a universal time and ageing of the universe. This universal time cannot be read by clocks which may run at different rates in different time frames

...I would welcome suggestions as to how this universal time might be measured...

Have you read the thread "is spacetime absolute?" where Martin and I discussed universal time?

With today's technology universal time, not to be confused with absolute time that does not exist, is in most cases an abstract thought experiment at best. What martin suggested is a universal time using a clock at rest with the CMB and in the absence of gravity. Any location could then adjust their clock for movement and gravity to have a synchronized clock with universal time. It would move at a different rate then local time clocks but that is ok. You would still have two locations or frames that had synchronized clocks and could share the same "now".

Because of continous movement in the cosmos, you would almost need an automatic gravity meter and CMB speedometer attached to an atomic clock for it to work. Maybe someday in the future this will be possible. Today's technology has allowed us to adjust the clocks on the GPS satilites for SR and GR so we can have a universal "now" in different frames.

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FTL = Faster Than Light.

### A Universe without Time

without ftl communication it cant be measured. entanglement may or may not provide ftl communication.

What is "ftl"? Just because something can not be measured does not mean it doesn't exist.

### Does my avatar annoy you?

...antmirer...If your specific image bugs (heh) him,...

Thanks Mr. Skeptic. I like your pun and other ways of saying things. Stuff moving on a computer screen has become a way of life, even though I am not crazy about it. So maybe I shouldn't contribute.

### Shape of a light flash

Right, but that's not really relevant to the question at hand, is it? The question is how does being in a different reference frame from a light source affect how the light propagates. The OP suggested that the lighted region would be elongated in the direction of travel. I'm suggesting it would be neither elongated nor compressed. (Although the observers in the two frames would not agree on the borders of the sphere, even if both agreed it was the same shape, because space itself would be compressed).

"I think you need to specify what the set up is." and "2) Light always travels at the same rate, C, in every direction relative to the observer, no matter what the relative velocity of the source to the observer."

so I crawled into that can of worms when you opened it.

The original post said:

Shape of a light flash

Are those both facts true :

a ) Suppose a circular wave is made in water, when seen from a plane, this is a moving circle

b) Suppose a light flash was emitted in vacuum, when seen from a fast moving observer, this should be an ellipse (longer in the direction of the speed) ?

Not sure what the "circular wave" in "water" has to do with the "shape of a light flash" or part b).

Other then that, I agree with you.

### Does my avatar annoy you?

The correct question should sound like this: "Does my avatar annoy/distract you while reading the posts?"

Bob.

you make a good point. I wonder if those that have seen it for awhile have just gotten used to it. It was distracting to me at first but not any more. Ants do not live forever and my eyes are open for a replacement. One more negative and I will look for the bug spray now.

### Shape of a light flash

Hehe, was there a black hole added to this question when I wasn't looking?

I added one to make my point more obvious. I see the entire universe as a variable gravity frame that does have an impact on light. In most cases the effect the would be small, especially over short distances.

### Shape of a light flash

...But it seems like any effect would be symmetrical, no? ...

If you could isolate a brief segment of the Sun's light as it left the Sun, it would seem almost symmetrical, for awhile. If you followed that brief segment (in real time) until it reached the outer limits of the milky Way on one side and the huge black hole at the center on the other, it would be far from symmetrical.

When light enters a high gravity area, an outside observer will see the light slow down. I look at it as space is curved and the light has further to go to cover the same distance. if you are in the same frame with the light, your clock slows down so the light speed is still constant.

If my layman vision of relativity is wrong, please straighten me out. I am here to learn.

Edit - Another way to put it is that if time slows down when you approach a black hole, the speed of light must slow down to maintain 186,000 miles per second.

### Shape of a light flash

...The ball of light itself, obviously, would still just be a uniformly expanding sphere.

Are you saying the light would NOT be influenced by gravity?

### Shape of a light flash

My question is, are you talking about the actual shape of the light as if you could see it in real time? Or as it would be seen by your eyes using only the light that did reach you and when it reached you?

I thought the speed of light is constant, but only relative to the frame it is in. Since the only light you can see is what reaches your eyes, it is in your frame and the speed will be constant. The actual shape would be distorted by gravity and other things.

### The stars....

are really used as a base to estimate the age of the universe? The oldest stars we see are "some of the first"?

Thats like looking at the oldest living human who is say 115 years old and using them to estimate that the human race started 115 years ago.

I see it as looking at light that took 13+ billion years to get here and seeing a new born.

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...If the most distant star is (for example) 90 billion light years away, then we know that the universe is at least 90 billion years old. And since the light from the star that we observed took 90 billion years to get here, that should make it one of the oldest as well.

Don't forget about the expansion of space. Light that took 13 billion years to get here was emitted from a galaxy when it was 3.3465 billion light years away and is now 29.701 billion light years away.

### Does my avatar annoy you?

Moderators, I hope you will let this run for a short while here since many of my post are here. Thanks

I received a PM from a new member (I will not name) and he said:

---------

"Hello,

I find you avatar to be annoying. It bothers me. It makes me sick. Could you change it for something really positive, please? I need positive emotions, not irritation.

Thanks."

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I do not want to make anyone sick or annoyed. I thought it was funny and now I am just used to it and my post are easy to find.

Is it time to step on the ant?

### Setting up a poll

I am having trouble setting up a new poll. I check the poll box at the bottom but it doesn't do anything.

Edit - Never mind, I figured it out.

### 13 billion year old GRB

http://www.astro.ucla.edu/~wright/CosmoCalc.html

When I plug 8.2 into where z is supposed to go and click Flat, I get 30.016 Billion LY away currently.

When I plug in 7.875 I get exactly 13 billion light years old and 29.7 billion light years away from us now. z=8.2 gives me 13.035 billion years old.

I see the problem though, I read a different article that rounded the #'s.

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Perhaps that came from taking the "surface of the balloon" analogy for expanding space too literally? It isn't accurate, though.

I found it. It was a combination of my imagination and that darn "Where Does Space End? It Must End Somewhere!" thread. My version of a non mainstream view. Glad I got that out of my head.

### 13 billion year old GRB

Great find! Thanks. Estimated redshift z = 8.2

I got z=7.875. Where am I going wrong?

(Edit - Ignore this line because it is from a different source)

Another thing I do not understand is the article said

" Distortions in the light signature of the object show it is 13 billion years old -- at the speed of light, 13 billion light-years away"

(Edit - From a different article then posted)

It can't be both because of the expansion of space but it is obvious they are saying it is 13 billion years old NOW. That would make it .665 billion years old at the age of redshift. The Ned Wright site also says it would have been 3.3465 Gly away when the light was omitted and is currently 29.7billion light years away.

My question is, if the universe was only .665 billion light years old when this GRB was omitted, is that long enough for a star to have formed, matured and then exploded?

If I am missing something here just tell me to get more sleep.

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Not likely, IMO. If it's a sphere, then all spacetime is on the surface of said sphere... The concept of a "center" or of something "inside the sphere" is completely meaningless.

I may be wrong but I thought a thick skinned sphere was one possibility. Not sure where that thought came from at the moment. My imagination is fairly active.

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It must have been a short-lived star...

You beat me to it.

### 13 billion year old GRB

The universe doesn't have a center. Or the center is everywhere, depending on how you look at it. To see the oldest light in the universe, you can look in any direction.

if the universe ends up being a 3-D sphere, couldn't it have a center?

### ????

Why is time bound to space? If space bent like a wormhole does time change? obviously not, but why not....

Time is bound to space so we do not have to deal with an extra dimension. The math works out well.

Time, like the speed of light, is constant. But only relative to its current location or frame that it is in. Bent space, because of gravity, will change the duration of one second relative to another frame. Your speed relative to other matter will also change the length of time segments.

### Randomness or Decisive?

...or is there something that decides what happens...

Would that "something" be a God?

### Just how fast and unexpected life could end

Walking into my home without knocking.

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