# 29.7 The anthropic principle  (Page 5/19)

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## Thought questions

What is the most useful probe of the early evolution of the universe: a giant elliptical galaxy or an irregular galaxy such as the Large Magellanic Cloud? Why?

What are the advantages and disadvantages of using quasars to probe the early history of the universe?

Would acceleration of the universe occur if it were composed entirely of matter (that is, if there were no dark energy)?

Suppose the universe expands forever. Describe what will become of the radiation from the primeval fireball. What will the future evolution of galaxies be like? Could life as we know it survive forever in such a universe? Why?

Some theorists expected that observations would show that the density of matter in the universe is just equal to the critical density. Do the current observations support this hypothesis?

There are a variety of ways of estimating the ages of various objects in the universe. Describe two of these ways, and indicate how well they agree with one another and with the age of the universe itself as estimated by its expansion.

Since the time of Copernicus , each revolution in astronomy has moved humans farther from the center of the universe. Now it appears that we may not even be made of the most common form of matter. Trace the changes in scientific thought about the central nature of Earth, the Sun, and our Galaxy on a cosmic scale. Explain how the notion that most of the universe is made of dark matter continues this “Copernican tradition.”

The anthropic principle suggests that in some sense we are observing a special kind of universe; if the universe were different, we could never have come to exist. Comment on how this fits with the Copernican tradition described in [link] .

Penzias and Wilson’s discovery of the Cosmic Microwave Background (CMB) is a nice example of scientific serendipity —something that is found by chance but turns out to have a positive outcome. What were they looking for and what did they discover?

Construct a timeline for the universe and indicate when various significant events occurred, from the beginning of the expansion to the formation of the Sun to the appearance of humans on Earth.

## Figuring for yourself

Suppose the Hubble constant were not 22 but 33 km/s per million light-years. Then what would the critical density be?

Assume that the average galaxy contains 10 11 M Sun and that the average distance between galaxies is 10 million light-years. Calculate the average density of matter (mass per unit volume) in galaxies. What fraction is this of the critical density we calculated in the chapter?

The CMB contains roughly 400 million photons per m 3 . The energy of each photon depends on its wavelength. Calculate the typical wavelength of a CMB photon. Hint: The CMB is blackbody radiation at a temperature of 2.73 K. According to Wien’s law, the peak wave length in nanometers is given by ${\text{λ}}_{\text{max}}=\frac{3\phantom{\rule{0.2em}{0ex}}×\phantom{\rule{0.2em}{0ex}}{10}^{6}}{T}.$ Calculate the wavelength at which the CMB is a maximum and, to make the units consistent, convert this wavelength from nanometers to meters.

Following up on [link] calculate the energy of a typical photon. Assume for this approximate calculation that each photon has the wavelength calculated in [link] . The energy of a photon is given by $E=\frac{hc}{\text{λ}},$ where h is Planck’s constant and is equal to 6.626 × 10 –34 J × s, c is the speed of light in m/s, and λ is the wavelength in m.

Continuing the thinking in [link] and [link] , calculate the energy in a cubic meter of space, multiply the energy per photon calculated in [link] by the number of photons per cubic meter given above.

Continuing the thinking in the last three exercises, convert this energy to an equivalent in mass, use Einstein’s equation E = mc 2 . Hint: Divide the energy per m 3 calculated in [link] by the speed of light squared. Check your units; you should have an answer in kg/m 3 . Now compare this answer with the critical density. Your answer should be several powers of 10 smaller than the critical density. In other words, you have found for yourself that the contribution of the CMB photons to the overall density of the universe is much, much smaller than the contribution made by stars and galaxies.

There is still some uncertainty in the Hubble constant. (a) Current estimates range from about 19.9 km/s per million light-years to 23 km/s per million light-years. Assume that the Hubble constant has been constant since the Big Bang. What is the possible range in the ages of the universe? Use the equation in the text, ${T}_{0}=\frac{1}{H},$ and make sure you use consistent units. (b) Twenty years ago, estimates for the Hubble constant ranged from 50 to 100 km/s per Mps. What are the possible ages for the universe from those values? Can you rule out some of these possibilities on the basis of other evidence?

It is possible to derive the age of the universe given the value of the Hubble constant and the distance to a galaxy, again with the assumption that the value of the Hubble constant has not changed since the Big Bang. Consider a galaxy at a distance of 400 million light-years receding from us at a velocity, v . If the Hubble constant is 20 km/s per million light-years, what is its velocity? How long ago was that galaxy right next door to our own Galaxy if it has always been receding at its present rate? Express your answer in years. Since the universe began when all galaxies were very close together, this number is a rough estimate for the age of the universe.

I l don't understand questions
which quesrions?
Ankit
How to make a telescope
Steve
***wikihow.com/Make-a-Telescope
Jennifer
optical mechanics
Astro
aptical
Nkateko
Which one has the ring
Saturn venue and even Jupiter all have rings the rings on Jupiter, however, aren't so easily noticed due to them only being viable through infrared
Hunter
visible *
Hunter
they each have three rings but not as you might think just think of them all as one big ring because that's basically what they are but they are desperate individual rings
Hunter
separate*
Hunter
can you tell me what is a quantam elighment? Lets see how many people give write answers
can you tell me what is a fomalhaut?
gdjm
Fomalhaut Is The Brightest Star In The Constalellation Of Piscis Austrinus.....
joe.
Tracy
Do You Mean Quantum Entanglement?
yes
gdjm
No Adam fomalhaut mean eye of universe
gdjm
quantum entanglement is when a husband has been married so long to his wife that he is directly influenced by her action usually in an opposite way. 🤣
Jocofranc
It Is Also The Brightest Star Of The The Constalellation Of Piscis Austrinus.....
who was the first person to get to the planet
Isaac
can anyone tell me daily rotation of the sun in tokyo
tokyo has it's own personal sun
Tracy
can you send me any pictures of the tokyo sun
Liridona
sure! ig?
Tracy
here can u?
Liridona
no it wont let me sadly
Tracy
or
Liridona
snapchat
Liridona
i dont have snapchat 😰
Tracy
okay ig
Liridona
my ig is fatwigga37 if you'd like to see :)
Tracy
Can we use SI units in the equation of Kepler's third law?
can u tell the equation pls
sasmita
how does religion enters to this topic when god created this world
Sakira
How Do You Know A God Created Our Planet?
Sakira
u must the bible
Sakira
How Do You That Book Is Authentic? And I Have Read The Bible, The Koran, The Torah And The Urantia.....
The law is T^2 is proportional to R^3 where t is planet's time period and r is average of semi major axis and semi minor axis. Also,don't turn this place into a religious warzone. We already have idiots fighting about religion.
priyanshu
If I Had A Book That Said Insects Created The Universe, Would That Make It Fact?
Have You Ever Heard Of The Council Of Nicaea?
Through Out History Mankind Has Worshipped Over 5000 Different Gods, How Do You Know Christ Is The True God?
God Is A Hypothesis..... The Definition Of Faith Is Belief Without Proof.....
Thank You Prianshu Roy, This Is A Forum For Science Not Archaic Stories Written By Sheep Herders, Well Said.....
Hebrew 13:1
onome
P2 = a3
So You Quote A Bible Verse, Now What?
Science Discourse Nothing Else.....
god is real he's not just a wise guess
Sakira
god bless you
Sakira
u know what,u are not here if god werent there!
Sakira
Science Discourse, Nothing Else.....
Thier Are Many Religious Sites You Can Go To, To Discuss God.....
hahahaha
Sakira
Have A Great Day.....
night time here
Sakira
Look Up The Definition Of Day, Instead Of Trying To Look Witty, Again Have A Great Day.....
😈😈😈
Sakira
such an socratic person?
Sakira
What Was Your Intention In Stating "Night Time Here" ?
please don't fight over silly stuffs!
Romancho
tangina mo
Sakira
No I Don't Believe A God Exist, But I Will Fight For Your Right To Worship Any God You Wish.....
no fighting
Sakira
But This Venue Is For Science Discourse.....
i know!
Sakira
No Fighting, Just Discussion.....
yes Naiyu, we have to use SI unit in the equation for the Kepler's every laws
Thanks.
Naiyu
wow
Kenneth
what's the scene of voyager 1,did we get any information through it
we are getting a lot of info yet more to be received check official mission report from the officials site ....
Ganeshan
what are the best astronomy books?
what is the parallel space?
neehar
how to measure the brightness of a star in w\m^2
it's based on the percentage of helium I think
neehar
ok TQ😊
Aarushi
it's based planet colour and brightness which called lumiosity
gdjm
Are there planets that has the same characteristics as earth.
yes ofcourse there are earth like planets but they aren't completely like earth.still scientists have a hope of life existence in there.
Aarushi
yeah of course example is Mars but they only discover water at mars
neehar
there's a much possibility of presence of earth like planets in the universe if they were present at goldilock zones
Jashwanth
what are goldilock zones?
Aarushi
why yes there are planets just like earth out there somewhere we know that much for sure given the number of planets in the galaxy, as a matter of fact, one of Jupiter moons officially named "gamamede" is very much like earth in size and characteristics
Hunter
How to become an astronomy
astronomer*
Emilya
Yes
Aakarsh
Astronomer
Aakarsh
yes i Also want to know the answer
Mehar
How to become?
Aakarsh
Me too
Romancho
By hard study
Zulker
Try to keep all the basics of science subjects and also English
Zulker
Ya i know that I will do hard work but
Aakarsh
I have always found astronomy fascinating, but my first love is philosophy.
GARY
I wanna become astromer as neel armstrang
Aakarsh
that's an astronaut
Emilya
Neil Armstrong
antman
what is your name who are you where are you why are you there
GARY
Neil Armstrong was an astronaut. You first work is to know the meaning of astrophysicist, astronomer, astronaut, astrologer and to find the work of the individual. And the most important thing is to be good in English. Because u have done some mistakes while doing chat with me like :an astronomer
Zulker
sorry I'm talking to somebody else someplace else on the internet
GARY
The heading will be "How to become an astronomer"
Zulker
jus be yourself and follow your passion and I think there is no need to copy anyone
Aarushi
hey it's simple yaar, it's based on your curiosity
neehar
what is the length of Earth
The Earth is not a perfect sphere, however it's roughly 25,000 miles, or 131.5 million feet, or 1.6 Billion inches. In the Metric system its HUGE!
Jocofranc
nyo
But can I also know and calculate the whole weight of earth includeing flora, funa,water on earth even air's weight.Depending on super compruter, I think it can be.For the very detail in the Metric System.Such as kilogram and pound.
nyo
Earth is about 6 Sextillion metric tons check out formula at ***science.howstuffworks.com/environmental/earth/geophysics/planet-earth-weigh.htm
Jocofranc
thank again Sr.I wanna ask another question if you don't mind.The earth had 4.5billion years age old.My question is from fire ball to today more and more stable geology was how happen.Please answer me starting of life on this planet and how many era are there and the earth history.
nyo
My friend you have asked a question(s) that scientists struggle with. There is no short cut...the information is lenghty. Here is an additional site for you. It is a good place to start. ***newscientist.com/article/dn17453-timeline-the-evolution-of-life/
Jocofranc
Sr,your web site is very useful to me.And another question is how gene or DNA transfer from parent to sibling.how we know the first DNA of our first human from arfarica.
nyo
Jocofranc
If speed is so many thousand time of light and start to travel from one point,how speed will return to it starting point even in straight line back.Will time and energy be limit it?Can it be posible.Please let me explain Sr.
nyo
hey neo ur curiosity is great, where r u from?
neehar
in physics actully no but thory make possible
gdjm
earth is about 13,000 kilometers across
Hunter
there is aliens or parallel universe
There may be both who knows
Debabrata
It would be quite surprising to me to learn that there is no aliens in our very own galaxy. The size of our galaxy alone seems to favour life. There's so many reasons why we haven't made contact but as our technology grows we will undoubtedly find answers. I also think that it's possible that ...
Jocofranc
But I don't think that that alien species might be developed.... Because if they were developed or advanced than us then they must have located us first and might have even contacted us
Debabrata
many other universes exist. I don't think that they would be parallel universes in the purest sense of the word. Only speculations on my part. We simply dont know with certainty.
Jocofranc
Hi Debabrata; You may be right. It's hard to say with certainty. An ugly truth (guess really) is that Tellurian are simply not interesting. We are not all that!
Jocofranc
Yeah Jocofranc you are also right about parallel universe. Who knows what lies ahead.
Debabrata
the parallel universe theory is something secondary but first let's focus on the nearby objects like titan which shows great hope
Aarushi
I read it before about aliens, but I have to research on it
neehar
yeah of course
neehar
What about XTs... Exo-Tellurians. Ancient people who could have obtain a spurt of technology and left home. Progression of men r not always linear but sometime cyclic. Civilization comes and goes. Geo-upheaval can easily erase any evidence. Our bros r out there. (have fun 😁)
Jocofranc
sir jocofranc I think u didn't listen about aliens who send a message to our space research organization.
neehar
what is inside Jupiter how it will rain there
interesting question!
Mahesh
would love to learn about it 😃
Morrie
jupiter is a gas gaint so you can't walk on the surface like here on earth, but there is a solid core.
Yannick
The latest term being used is a 'fuzzy core'. An inbetween of solid and liquid. Check ***sciencemag.org/news/2019/08
Jocofranc
I think it based on the nature of the source in Jupiter
neehar
Scientists believe that onJupiter and Saturn, it rains diamonds. New atmospheric data for the gas giants indicates that carbon is abundant in its dazzling crystal form, the BBC reports. Lightning storms turn methane into soot which hardens into chunks of graphite and then diamond as it falls.
gdjm
Where is a moon HOW MANY KILLOMETER FAR FROM EARTH
On Average 383,000 Kilometers, Between Perigee And Apogee.....
386,000 km
neehar
3.6×10^5 km
gdjm