Discussion in 'Astronomy, Exobiology, & Cosmology' started by Hayden, Jul 19, 2018.
It wouldn't. It's taking 13 billion years to reach us now at our current position.
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All right man, that is obvious. You haven't understood the point or I have not been able to articulate it properly.
Maybe you should make that point clearer? What is your point?
1. We have received a light from a galaxy which was emitted 13 billion years ago.
2. At that time the universe was of 400 million years old.
3. Assuming that the total span of the universe at that time was only 800 million light years.
4. That means the distance between the galaxy and the earth (imaginary point where the earth will be after billions of years) at that time was less than 800 million light years only.
5. If there was no expansion then the light could have reached this point in just under 800 million years.
6. If there was expansion at half the speed of light, even then this photon would have reached in less than 2 billion years after emission.
7. But when the universe was just 400 million years, the Hubble law does not predict even such high expansion rate, so light would have reached the earth point much before 2 billion light years.
8. The light had no distance to cover which could have taken it 13 billion years to reach.
The only conclusion which I can draw is that at t= 400 million years after big bang, the universe was spatially very big, and the distance between this galaxy and the prospective earth point was much higher than mere 800 million light years or so. This indirectly concludes that at the end of inflation the size of the universe was very very big, may be billions of light years.
have you considered to put those numbers in the sketch of post #5, which shows the expansion of the universe (seen in the sphere #8 expanding to present size#3) through the time dimension.
If you could make a simple sketch, like this taken from "alma" thread in alternatives ,--- your query, argument would be clearer to all.
Ok, pl consider the sketch in #5.
The light was emitted from #7 when the universe was of inner (circle) sphere size.
Let us say at that time our present position was at the point on the line 4-5 intersecting the inner circle. We call it Pt B.
If there was no expansion this light would have covered the distance 7B in a comparatively short time.
But due to expansion, the point B has come to pt#5, so the different photon emitted at that time would require to cover 7-5, this time is 13 billion years for the question in hand.
Assuming that the inner sphere is just around of 400 million light years radius, then for 7-5 to be of 13 billion light years size, the expansion got to be very fast or the inner sphere has to be much bigger than 400 mly.
At the end of inflation the size of the Universe was very, very big. However, that's not even necessary for the light to be able to cover a time span of 13 billion years because we aren't talking about the size of the Universe then. We are talking about the size of the Universe now.
I said that before and you said that was obvious and that I've missed your point. What you seem to be missing is that the light from that galaxy has continued to shine so now when we observe it, it has been shining for 13.4 billion years.
That doesn't mean that at an earlier time it wasn't also shining. It doesn't mean that the light has just reached us for the first time. It only means that the light that we are now seeing, originated 13.4 billion years ago. Don't confuse age with distance.
The Universe was very big, right after inflation but even if it wasn't it wouldn't change the fact that light that we currently see was from 13.4 billion years ago.
The figures I've seen suggest that during inflation the exponential expansion was something similar to the size of our current Observable Universe every (whatever faction of a second) doubling.
Again, you seem to be suggesting that our Universe isn't currently large enough for something to travel 13.4 billion light years. The current Observable Universe is something like 94 billion light years in diameter.
What exactly do you disagree with in terms of our current scientifically accepted knowledge?
1. The sun light which we see now is not 24 hrs old, it was just emitted 8 minutes ago. So it does not matter how long the Sun has been shining we get a photon which was originated 8 mts ago at any instant.
2. Same with the galaxy, a photon originated at t = 400 million years, must have a path to cover to reach us at t = 13.4 billion light years even with the expansion around.
3. Your assertion that the size of the universe after inflation does not matter, appears to be incorrect. If the universe after inflation was small, implying universe at t = 400 million also small, then the distance to cover in 13 billion years require massive expansion rate, which is not supported by hubble.
Pl consider the sketch in #5.
Assume that inner sphere was the size at t = 400 million, and the outer sphere is present at around t = 13.4 billion years.
The time taken from 7 to 5 by light is 13 billion years, so the distance 7-5 is 13 billion light years. So the expansion should be in such a way that the point B came to point 5 in 13 billion years (B is the intersection point of inner circle with line 4-5). If the inner sphere is small then (7-5)~(B-5) which would call for an average expansion at the rate of c!
yes, in the sketch the expansion is not considered that of (through) space, but through the time dimension,( #2 past time, #2 infinite future time.) no wonder c would show up. Whenever it does you are on to something. but,
please make a sketch that fits your particular defined question, This one was done on squared paper photographed and posted.
Why would the universe not be expanding at close to the speed of light if it took a photon travelling at the speed of light 14 billion years to get here?
If I throw a baseball @ 100mph after a train going 99 mph @ 1 mile away from the pitcher, how long will it take for the baseball to catch up with the train? It's only gaining 1 mph on the train.
The sketch from "ALMA" is based on the assertion that the expansion of the universe through time is constant. Looking at time, the universe doubled in size in the first seconds, but expands through time now at the same pace, 300 ooo km max during that same length second in "circumference" of the model.
The ratio of expansion through time was inflationary in the beginning compared to now. just based on the linear geometric relationship between radius (expansion direction) and size (circumference).
The article said that it has been determined that the galaxy was first formed 13.4 billion years ago. I have to take that as a given. The Universe is expanding so that galaxy is now more than 13.4 billion light years away from us. I'm guessing it's 30 billion light years or so away from us.
All we know is that the photons reaching us now are coming from a distance greater than 13.4 billion light years.
I'm not going to comment on Nebel's sketch from the "Alternative Theories" sub-forum.
#48 does not refer to that sketch.
This makes no sense. It could be infinitely large and not expanding at all and that could still happen.
However, it is true that the Universe is expanding faster than the speed of light from the reference of two far removed galaxies from each other. That doesn't have to be the case however for a photon to take 14 billion years to get here.
Nor does my response to you in post 53.
Can you 'now' see the light emitted by Sun 10 mts ago?
You can't because it takes only 8 mts for the light to strike us.
For us to see a light emitted 13 billion years ago, the coincidence be such that the expansion rate should bring us in the path of that photon after 13 billion years.
My point is expansion is much slower if the size after the inflation is small. Expansion rate is around 8000 km per second for a spatial distance of 400 million light years, which is around 0.03c, much slower than the required c. So if the universe was around 400 million light years in size at the time of emission, those photon would have never reached us after 13 billion years, like the light 10 mts ago is not detected by us now.
This may be illustrative:
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The OP headline asked a "time" question. Now the discussion is asking the universe "how big were you when you were 400 000 year, 13 billion year old ?", a size question. The sketch in post #5 addresses the "time" question. If there really was a hyper c inflation, and you wanted to show spatial size, expansion in that hypothesis, the inner , smaller older sphere would have to much larger, the slope of the line #0 more horizontal, nearer to the slope #5-6.
Here, as a reference only, is the legend of the time application of the sketch. (alma page 35 #681)
# 1 is timespace of the future that the universe expands into into. aka energytime.
#2 is the past timespace that the membrane sphere #3 has moved through from the BB # 4, an area, volume, that is now void of gravity, other fields and any information.
#3 is the zero thickness membrane that is thought of to contain all matter of the universe. ( zero thickness because it's zero dwell on its movement into the future).
#4 is the point in timespace of the BB big beginning, now empty.
#5 is showing the observer's location (Hubble telescope in this case of deep space viewing)
#6 is the location of the MAC1 oldest, far star seen so far, so far away in time (2/3 to the horizon #9, which is allowing us to see only back to the BB cbmr).
#7 is the exit point in the past, timespace, where the image of the far star that Hubble captured, originated, on the then smaller universe #8.
#8 is the size in time of the universe when the light that Hubble received from MAC1 was emitted.
#9 is our horizon from our current position in the universe, with a radius of ~13 BLYs along the membrane surface. (the rim of the umbrella)
#10 is the possible position of the farthest star, ~ 40 BLYs away, halfway around the universe / membrane sphere. > 2 horizons away.
#11 is a correction point accounting for the curvature of the membranes surface vs circumference. (also for 3/3.14 hex vs circle)
#12 is the position of an astronomer elsewhere in the universe, that also could see that far star, but from the other side. lucky lady!
#0 is the shortest path that the photons took from the small beginning in early universe #8 at point #7 to the observation point at our hubble detector at # 5. ( track could have been longer because of proper motion). Far star'simages' light came from point #7, but was seen as coming from #6, along the membrane #3, the direction #6 in the current position of the far star
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