2
votes
1answer
51 views

Time Energy symmetry in General Relativity (not asking about energy conservation)

In General Relativity is there a TE symmetry similar to CPT symmetry in the Standard Model ? It's pretty easy to understand that by flipping charge and parity you merely get a time reversed equivalent ...
0
votes
1answer
56 views

How has the age of the Universe been derived from the observations made by the Planck mission?

The parameters of $\rm\Lambda CDM$ model have been determined to an amazing high precision from the measurements made by the Planck mission. In particular, the Hubble "constant" (the value of Hubble ...
-1
votes
2answers
112 views

I understand the Big Bang Theory (BBT), but how was the matter in the BBT created?

I understand the Big Bang Theory to consist of all of the matter being pulled into one great gravitational pull. such a great force that it expelled the matter out causing the idea of Red-Shift and ...
1
vote
3answers
92 views

Expansion of the Universe regarding Time and lightspeed

According to our current understanding, the universe is expanding... it is often said that every galaxy is moving away from us (I'm assuming that isn't true for galaxies in our local group), and it's ...
1
vote
1answer
82 views

Is the Universe Past-Eternal?

Does the Borde-Guth-Vilenkin theorem definitively demonstrate that the Universe cannot be past-eternal, whatsoever? Does it not assume a classical space-time while the real world requires Quantum ...
0
votes
1answer
120 views

What's the meaning of the age of the universe?

I'm not asking about how we worked backward from an expanding universe to the age of the big bang, but rather what is the meaning of time in a near infinitely dense point in the context of general ...
21
votes
2answers
1k views

The age of the universe

Many times I have read statements like, "the age of the universe is 14 billion years" . For example this wikipedia page Big Bang. Now, my question is, which observers' are these time intervals? ...
-3
votes
3answers
167 views

Is Space conserved [closed]

Can space be created or destroyed? Is space conserved? I am not asking for matter,energy and time. Its just a question about conservation of space PS: I am asking for what was there before big bang. ...
0
votes
2answers
125 views

How could mass exist before Big Bang?

I heard that before Big Bang the temperatures were so high that mass and energy constantly converted to each other. After big bang the temperature became less and the conversion stopped that is what ...
2
votes
2answers
728 views

Can Flow of time become still?

According to theory of time dilation, flow of time slows down significantly at the speed of light.Is there any conditions practically or theoretically when flow of time is reduced to zero means it ...
1
vote
0answers
83 views

Time-Independent Gravitational Equation?

Is it possible to calculate gravitational induced position change without requiring the use of time (and therefore, acceleration) anywhere in the equation? If such an equation were to be discovered, ...
5
votes
3answers
187 views

Is isotropy a fundamental/invariant feature of our universe, or is it merely a convenient, albeit arbitrary, feature of some reference frames?

This is related to a previous post. Assuming that the Cosmological Principle is correct, does this imply that the universe possess an empircially privileged reference frame? What I am trying to ...
7
votes
2answers
273 views

Assuming that the Cosmological Principle is correct, does this imply that the universe possess an empirically privileged reference frame?

OK...before everyone blasts this with references to the relativistic invariance of the physical laws, time dilation, etc let me add some context. Also, I am an amateur with an interest in physics, so ...
8
votes
1answer
133 views

Different age of universe

According to general relativity time runs slowly near a massive body. So, I have a question bothering me from some time, that if time for every body/object in universe runs at a different rate, then ...
0
votes
0answers
41 views

Calculate age of the Universe at 7 billion and 28 billion years old [duplicate]

If $1 / H_0 $ is about 14 billion years, then what happened when the universe was half its current age? Is the empirically determined $H_0$ supposed to have been twice its current value? And when ...
-4
votes
1answer
139 views

Does the big bang violate the conservation of energy? [duplicate]

It is a fact that a thing is existing now because it had already been created. So why don't we take this to account to redefine law of conservation of energy.
6
votes
0answers
99 views

Time diffeomorphisms breaking in inflation

I am currently working on the topic of inflation. It seems that at the stage of inflation, the universe can be described as a de Sitter space. In such a space, all spacetime diffeomorphisms are ...
2
votes
3answers
800 views

Scale factor and age of the universe

Why is the cosmological scale factor (expansion rate of the universe) not simply the time $t$, i.e. the age of the universe?
11
votes
1answer
1k views

What could explain the measurements that the Methuselah star is older than the universe?

So there has been talk in the news of a star named Methuselah that is "older than the universe". Moreover, this star happens to belong to our very own Milky Way. The article mentions that Methuselah ...
0
votes
1answer
625 views

Is time slowing down and disappearing from the universe instead of the expansion of universe? [duplicate]

Are we fooled into thinking that expansion of the universe is accelerating, when in fact, time itself is slowing? Or if dark energy does exist?
0
votes
1answer
1k views

Did space and time exist before the Big Bang? [duplicate]

I accept the Big Bang theory. What I can't understand is how there can be a where or when to the Big Bang if space time did not exist prior to it. Did space and time exist prior to the Big Bang?
3
votes
3answers
442 views

Looking out into the universe means looking back in time - how does that work?

This is a question that has been gnawing on me for many years now. Back a long time ago, as I recall in reference to a scene in a popular science show on TV, I was asked the following. The claim is ...
2
votes
1answer
146 views

Does our local time speed up as the Universe expands?

Starting from a simplified radial Freidman Walker metric we have $$ds^2 = -c^2 dt^2 + a(t)^2 dr^2 $$ How does one measure one's proper time operationally? One times a light beam along an element of ...
2
votes
1answer
105 views

What was ticking just after the Big Bang?

When reading about the Big Bang, I see phrases like 3 trillionths of a second after... So, what was ticking to give a time scale like this? We define time now in terms of atomic oscillations, but ...
12
votes
4answers
7k views

The meaning of imaginary time

What is imaginary (or complex) time? I was reading about Hawking's wave function of the universe and this topic came up. If imaginary mass and similar imaginary quantities do not make sense in ...
0
votes
1answer
387 views

Does the Earth's revolution around the Sun affect radioactive decay?

Premises: The radioactivity is either hastened or slowed inside a fast moving aircraft. Speed of fastest aircraft: 3,529.6 km/h. The earth's revolution is: 107278.87 km/h. The earth's ...
2
votes
0answers
428 views

Is large-scale “time reversal” (Poincaré recurrence) possible given infinite time?

The following are some assumptions I'm basing my question on, from what (little) I understand of physics. I list them so an expert can (kindly) tell me where I'm going wrong. There is a probability ...
1
vote
1answer
199 views

How precisely can we date the recombination?

The early universe was hot and opaque. Once it cooled enough, protons and electrons were able to form hydrogen atoms. This made the universe transparent, and was known as recombination. We can see the ...
1
vote
1answer
1k views

Relation between comoving distance and conformal time?

In cosmology, we have two quantities and I want to understand the physical relation between these two : $\chi = \int_{t_e}^{t_0}c\frac{dt'}{a(t')}$ : the comoving distance with $t_e$ the time at ...
2
votes
1answer
2k views

What did Hawking mean? 'Time started at the big bang'. Book suggestions please [closed]

After writing down this question, I have come to realize that. What I really want is reading materials on the questions below. Before the big bang there was no such thing as 'time' (Steven Hawking on ...
4
votes
5answers
151 views

Could there be more universes?

In the documentary: "Curiosity - Did God Create the Universe (on YouTube)", theoretical physicist and cosmologist Stephen Hawking states that time did not exist before the big bang. The first ...
1
vote
0answers
106 views

Confusion with infinity and time [closed]

I have some confusion between with resolving the following situation. I know that no measurable quantity can have a value of infinity. For example, I just wrote something out, but clearly this ...
9
votes
3answers
97 views

Seeing cosmic activity now, really means it happens millions/billions of years ago?

A Recent report about a cosmic burst 3.8 billion light years away. It is written as though it is happening now. However, my question is, if the event is 3.8 billion light years away, doesn't that mean ...
0
votes
1answer
191 views

If you removed every particle from space…? [closed]

I'm trying to find something Einstein (I think) said about time...It was something like.. "If you removed every particle from space and were left with only one pocket watch (clock, timepiece?), time ...
6
votes
2answers
942 views

on causality and The Big Bang Theory

With the notion of causality, firmly fixed by GR, we derived the concept of a singular point from where space-time begun. Causality alone gives us the possibility to talk about a known past (i.e. ...
11
votes
4answers
3k views

Did time exist before the creation of matter in the universe?

Does time stretch all the way back for infinity or was there a point when time appears to start in the universe? I remember reading long ago somewhere that according to one theory time began shortly ...
4
votes
2answers
547 views

Big bang and time

I heard Carl Sagan talking about the Universe 15 Billion years ago, and the Big Bang. He made the statement that it was the biggest explosion of all time (at first I thought this a subtle pun). This ...