There is a causal horizon to our known universe (that is set by the speed of light), which is constantly receding
as time goes on. Beyond that, we can have no access or direct knowledge of any kind. However, we will not
continue to see more of the universe indefinitely, since its expansion is accelerating. This means that eventually
we will see only our (gravitationally bound) local group and nothing else, just empty space out to the horizon.
as time goes on. Beyond that, we can have no access or direct knowledge of any kind. However, we will not
continue to see more of the universe indefinitely, since its expansion is accelerating. This means that eventually
we will see only our (gravitationally bound) local group and nothing else, just empty space out to the horizon.
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Scientists have been observing the universe for all of history (with either no, or then current instruments).
We have plenty of time, about 150 billion years, before the permanent darkness begins. We can only see
back to 400,000 years after the bang, due to universal plasma blocking light transmission before that time.
It's ironic that the old "island universe" theory of our galaxy will then be correct.
We have plenty of time, about 150 billion years, before the permanent darkness begins. We can only see
back to 400,000 years after the bang, due to universal plasma blocking light transmission before that time.
It's ironic that the old "island universe" theory of our galaxy will then be correct.
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Keep our forum clutter free! Please do not quote the entire post just above yours.
There's no light to see from before t=400,000, since it could not propagate freely. The microwave radiation
from just after that time (due to the combining of electrons and protons into atoms, happening everywhere)
is also everywhere in the universe.
The time barrier due to the speed of light is different. Our visible horizon recedes directly with time.
That is, we see more and more of what was previously past that horizon (at least for now) as time passes.
As far as is currently known to be fact/theory (pretty much the same thing), the acceleration of the
expansion of the universe started several billion years ago, and continues.
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When dealing with air molecules, the mathematics are mind boggling!
Earlier I said there are approximately 30 million million million molecules in just 1 cubic centimetre of air at standard atmospheric pressure.
Now the diameter of an air molecule (O2/N2) is around 300 trillionths of a metre.
If we could possibly stack all the molecules in 1cc of air on top of each other, then the resulting line would stretch for around 9 thousand million metres.
That's around 11 times to the Moon and back!
P.S. Please feel free to check my maths - I may have lost some beads from my abacus! (Earth to Moon distance is approximately 400 million metres).
Earlier I said there are approximately 30 million million million molecules in just 1 cubic centimetre of air at standard atmospheric pressure.
Now the diameter of an air molecule (O2/N2) is around 300 trillionths of a metre.
If we could possibly stack all the molecules in 1cc of air on top of each other, then the resulting line would stretch for around 9 thousand million metres.
That's around 11 times to the Moon and back!
P.S. Please feel free to check my maths - I may have lost some beads from my abacus! (Earth to Moon distance is approximately 400 million metres).
Not hard, merely impossible!
However, the mathematics doesn't lie. I've simply updated the figures I once read in my old text book - 'Heat' by RG Mitton.
I'll add that the 30 million million million molecules which occupy that single cubic centimetre of air are, on average, 10 times their own diameter apart.
This means most of that tiny volume is empty space!
This makes it doubly difficult to comprehend that the molecules contained therein could, if placed end to end, stretch the hige distance I've calculated!
However, the mathematics doesn't lie. I've simply updated the figures I once read in my old text book - 'Heat' by RG Mitton.
I'll add that the 30 million million million molecules which occupy that single cubic centimetre of air are, on average, 10 times their own diameter apart.
This means most of that tiny volume is empty space!
This makes it doubly difficult to comprehend that the molecules contained therein could, if placed end to end, stretch the hige distance I've calculated!
A vacuum contains dark energy.
Dark energy is why the universe continues to expand and hasn't contracted back on itself due to gravity.
New research indicates that dark energy (and hence an accelerating universe) may not exist
and "might be an artifact of a fragile and false assumption."
New evidence shows that the key assumption made in the discovery of dark energy is in error
and "might be an artifact of a fragile and false assumption."
New evidence shows that the key assumption made in the discovery of dark energy is in error
Reading through that link, I take it that that a Type 1a Supernova can no longer be regarded as the 'standard candle' used for the measurement of cosmic distances.
If I understand it correctly, the brightnesses of T1a supernovae have recently been found to depend on how young they are - i.e. how far back in time we can observe them.
All T1a supernovae are therefore not of a standard brightness as previously assumed.
This would mess up our previous measurements of cosmic distances and put into doubt the accelerating expansion of the universe and hence the existence of the Dark Energy hypothesised to explain it.
Am I right?
If I understand it correctly, the brightnesses of T1a supernovae have recently been found to depend on how young they are - i.e. how far back in time we can observe them.
All T1a supernovae are therefore not of a standard brightness as previously assumed.
This would mess up our previous measurements of cosmic distances and put into doubt the accelerating expansion of the universe and hence the existence of the Dark Energy hypothesised to explain it.
Am I right?
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