Linked Questions

0
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0answers
219 views

Variation of Hubble constant in cosmological timescales [duplicate]

Although the Hubble constant appears to be a constant, it is not really a constant. Is the Hubble constant decreasing over cosmological timescales?
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0answers
76 views

Expansion rate in matter dominated era [duplicate]

Do physicists know what the expansion rate of the Universe was at the beginning of the matter dominated era?
1
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0answers
55 views

Calculating the age of the Universe at temperature 1 MeV [duplicate]

I've been told to calculate the age of the Universe at $T = 1 \, \text{MeV}$, assuming that $a(t=0)=0$. Now, I've already calculated the value of $H$ at that temperature, which was around $H(1\,\text{...
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vote
0answers
17 views

Hubble time and constant [duplicate]

Friedmann equation relates Hubble constant to Universe age as 1/H0 times mass density correction factor adding a few percent. What would Hubble have observed 7 billion years ago? The same value? if so ...
0
votes
0answers
16 views

What is the calculation of the Hubble time based on? [duplicate]

I understand that Hubble's law states that:$\\$ $v=H_{0}D$ However, given that the Hubble time (an estimate of the age of the universe) is given by $\frac{1}{H_{0}}$, doesn't that mean... $v=H_{0}...
275
votes
6answers
37k views

Did the Big Bang happen at a point?

TV documentaries invariably show the Big Bang as an exploding ball of fire expanding outwards. Did the Big Bang really explode outwards from a point like this? If not, what did happen?
25
votes
9answers
6k views

How can the universe expand if there is gravitation?

We live in an expanding universe - so I'm told. But how can that be possible? Everything imaginable is attracted by a bigger thing. So, why can't gravitation stop the expansion of the universe? I know ...
9
votes
2answers
14k views

Hubble time, the age of the Universe and expansion rate

The Hubble time is about 14 billion years. The estimated current age of the Universe is about 13.7 billion years. Is the reason these two time are so close (a) a coincidence, or (b) a reflection that ...
5
votes
3answers
6k views

Value of the Hubble parameter over time

There is something I don't understand about the Hubble parameter $H$, as it seems to clump two concepts together that I can't quite unify in my head. On the one side, we have $$V = D H$$ which means ...
6
votes
3answers
709 views

What was the density of the universe when it was only the size of our solar system?

What was the density of the universe when it was only the size of our solar system? Did it approach neutron star density? Is it physically correct to even ask such a question?
3
votes
1answer
1k views

Equation for Hubble Value as a function of time

I am trying to write the equation for the situation where the Hubble parameter $H$ would be changing over time. In other words, it would represent an accelerated expansion of the Universe. That is, $...
2
votes
2answers
2k views

If the universe is expanding will gravitational attraction eventually go to zero?

Let's assume that we prove that dark matter exists (after all, only about 4 percent of the entire universal mass is atoms, and 22% dark matter, 74% dark energy (I think I got the numbers right)). ...
5
votes
2answers
333 views

FRW metric and its validity througout the age of the universe

Why do we think that the FRW metric should be valid throughout the entire history of the universe?
3
votes
2answers
525 views

Accelerating expansion of the universe in numbers

The Earth's acceleration in numbers is $9.8\ \mathrm{m/s^2}$ and it stays constant in time. How much is the acceleration of the Universe expansion in numbers? I noticed that the Hubble constant (...
2
votes
2answers
538 views

Flat universe and accelerating expansion

As current data suggests that the universe is flat, a flat universe would imply a slowing expansion rather than an accelerating one which we observe. Neither in an open nor a closed universe there is ...

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