querious wrote:I spend a lot of time puzzling over this table that shows the current state of the Universe, in Planck Units.
If it's not a simple coincidence based on the current age of the universe, it means that the universe gets more massive as it ages, which is a strange notion. It also increases it's size in lock-step with it's age & mass. That's kinda weird, no?
D_Archer wrote:Planck length is also nothing fundamental, it is our smallest measure defined by the physical tools we use to measure.
Higgsy wrote:querious wrote:It seems to me that the choice of Hubble volume and stellar mass to compare in Planck units is rather arbitrary.
Higgsy wrote:D_Archer wrote:Planck length is also nothing fundamental, it is our smallest measure defined by the physical tools we use to measure.
Planck length and Planck time are not defined by the limit of our physical tools because they are much, much smaller than we can measure.
A Planck length is 1.6x10-35mm. The most accurate measurement of a length or length change is around 10-19m , so 16 orders of magnitude larger.
A Planck time is 5.4x10-44s. The shortest interval that can be measured is via an ultra-short laser pulse. The record was about a femtosecond (10-15s) about 30 years ago, but people are making attosecond (10-18s pulses now. Still that is a whopping 26 orders of magnitude longer than a Planck time. To give this some perspective, there are about the same number of attoseconds in a year as there are Planck times in an attosecond.
The Planck units are fundamental in the sense that they are culture and history independent and they are derived by setting a number of fundamental constants, such as the speed of light and the gravitational contant equal to 1.
This is the ï¿½quantum of lengthï¿½, the smallest measurement of length with any meaning. And roughly equal to 1.6 x 10-35 m or about 10-20 times the size of a proton
D_Archer wrote:I am pretty sure Planck length is a measurement, it says so in the defintion >This is the ï¿½quantum of lengthï¿½, the smallest measurement of length with any meaning. And roughly equal to 1.6 x 10-35 m or about 10-20 times the size of a proton
Unless modern science woo has abused the original idea by Planck i rest my case. I was taught it was about measurement.
Regards,
Daniel
querious wrote:Higgsy wrote:querious wrote:It seems to me that the choice of Hubble volume and stellar mass to compare in Planck units is rather arbitrary.
Point taken, but the age, Hubble constant, and Cosmological Constant also seem related to each other.
Higgsy wrote:Also, note that as far as size goes, what is commonly called the size of the universe should properly be called the size of the observable universe within the Hubble volume. It seems certain that the universe continues outside the Hubble volume, and the Hubble length depends on if and how the Hubble constant changes over time. (Yes, I realise it's called a constant, but it would not be constant in time for any non-zero second derivative of the scale factor - accelerating expansion or contraction).
It seems to me that the choice of Hubble volume . . . in Planck units is rather arbitrary.
It wouldn't.querious wrote:Higgsy wrote:Also, note that as far as size goes, what is commonly called the size of the universe should properly be called the size of the observable universe within the Hubble volume. It seems certain that the universe continues outside the Hubble volume, and the Hubble length depends on if and how the Hubble constant changes over time. (Yes, I realise it's called a constant, but it would not be constant in time for any non-zero second derivative of the scale factor - accelerating expansion or contraction).
It seems to me that the choice of Hubble volume . . . in Planck units is rather arbitrary.
If the actual universe was 50 times bigger than the observable universe, how would that affect our estimate of the age of the universe?
Not to the first order. The age of the universe is given by the Hubble constant and the current scale factor. So for example, the current measurement of the Hubble contant is ~70km s-1Mpc-1. So the distance of a galaxy at 100Mpc is increasing at 7,000km/s. Divide 100Mpc by 7000km/s to get how long ago that distance was zero, and hence the age of the Universe. 1Mpc is ~3x1019km, so 100Mpc/7000 is ~4.28x1017s or ~13.6 billion years. This result is for a Universe in which the expansion rate has always been constant. There is strong evidence for a non-constant rate of expansion and the best estimate of the age of the Universe based on data from the anistropies in the CMB is 13.8 billion years.Isn't the age estimate based on taking the current SIZE and expansion RATE and running the clock backwards?
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