# Time at big bang

In classical physics we took space and time as distinct absolute. But in GTR space-time continuum only come into play. Even at solar system level this exists as evident from problem of perihelion of mercury and definitely at the big bang moment. But how it is stated that plank time exist at 10^-43 sec after big bang distinct from space?

phinds
Gold Member
In classical physics we took space and time as distinct absolute. But in GTR space-time continuum only come into play. Even at solar system level this exists as evident from problem of perihelion of mercury and definitely at the big bang moment. But how it is stated that plank time exist at 10^-43 sec after big bang distinct from space?

Where does it say that and what, exactly, does it say ?

It is said time and space originate after planks time 10^-43 sec of big bang. Exact source I don't know but reading somewhere

phinds
Gold Member
It is said time and space originate after planks time 10^-43 sec of big bang. Exact source I don't know but reading somewhere

"reading it somewhere" is not considered a reliable source on this forum.

In your first post, you asked why something was "distinct from space" and now you are asking about both space and time. Your question is confusing and unclear.

If you look at the universe and the way it is expanding, it is clear that if you "run that movie backwards" there had to be a point in time where it all started to expand FROM. That point in time is called "t=0" or "the singularity".

Modern science has no idea what was going on at that time.

BUT ... what is estimated to be one Plank time after that, things start to happen in a way that can be strongly inferred from what we now DO know, so since nothing is known about the time of the singularity, we say that space and time started at one Plank time after the singularity.

The size and shape of the universe at that time is not known. It might have been infinite or it might have been finite but unbounded. What is known is that it had to be an incredibly hot, dense energetic plasma.

oK Thankyou for response. But time and space distinction is only empirical. At the moment of big bang could they be separate ?

bapowell
Nobody knows. We only have theoretical control of the universe after the Planck time, and empirically we've only touched on times after that.

Fredrik
Staff Emeritus
Gold Member
General relativity doesn't say that there's anything special about that time, or any other. One can argue that GR is likely to be wrong about what's going on during time intervals shorter than the Planck time, but this argument is at best a rough order-of-magnitude estimate.

If we trust the estimate, then it's reasonable to say that space as we know it (i.e. as described by GR) didn't exist before that time.

In classical physics we took space and time as distinct absolute. But in GTR space-time continuum only come into play. Even at solar system level this exists as evident from problem of perihelion of mercury and definitely at the big bang moment. But how it is stated that plank time exist at 10^-43 sec after big bang distinct from space?

you might be referring to the planch epoch, this is a SUSY descriptive. Essentially its a temperature derived epoch, that may or may not have happened depending on which symmetry breaking form turns out to be most accurate. Depending on which particle physics article you read describing the particle physics of the early universe will have different breakdowns of various epochs in the first second of the universe. These are based on what we understand of the interactions of particle physics and when different species of particles reach thermal equilibrium. Essentially the planck epoch

Begin:t’ 10−43 s,
T’ 1019 GeV’ 1032 K.
End:t’ 10−34 s,
T’ 1014 GeV’ 1027K

essentially it describes a point in time where All forces but gravity are uniﬁed, i.e .strong and electroweak. This is based largely on SUSY Grand unification theories. Essentially due to the temperatures and density of a smaller volume, any interactions that occur are unstable and the reverse reaction also occur. So even quarks and leptons cannot have stable reactions.

the next epoch is usually the GUT epoch other epochs include electroweak epoch, leption epoch, quark hadron epoch

but again it depends largely on which article you read lol, we simply cannot replicate the temperatures involved so much of this is a best guess based on what are current understanding of particle physics tell us

my personal favorite textbook that describes this albeit briefly is "Introductory to particle physics" by Peter Griffith although he doesn't bother breaking down the epochs. The temperatures and time period above is described from "Early universe particle physics" though I can't recall the author its from my notes and I can't locate the original, packed away still from my recent move

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Drakkith
Staff Emeritus
It is said time and space originate after planks time 10^-43 sec of big bang. Exact source I don't know but reading somewhere

Let's look at it from the reverse perspective. Since light has a finite speed, it takes a finite amount of time for it to reach us after emission. This allows us to look backwards into time and see what parts of the universe were like in different parts of the past. The further away the objects are, the further backwards in time we are seeing. (Note that this is not time travel, it's simply a time delay in the light reaching us) However, due to the expansion of space we actually cannot see past a certain point since the light is redshifted out of the visible and into the infrared and beyond. (Plus the objects we wish to view get too small and dim to detect due to their extreme distance and recession velocity)

Combining the observations we can make with models made using known physical laws, we can extrapolate what the universe was like before this point in time. When we do so, our model tell us that the further backwards we go, the more dense and hot the universe becomes. At a certain point the conditions of the universe become so extreme that the model we are using encounters a serious error; it stops making useful predictions. Instead, we get infinities in our math that we can't get rid of. It is at this point that "singularities" appear in our model and it is around this point in time that it is said "the big bang occurred". These singularities are mathematical singularities and there is nothing special about them. They simply represent where the math you are using stops working.

Note that nowhere in my post have I said anything about space or time coming into existence. The entire idea of a "real" singularity birthing space and time into existence is a misunderstanding. It is very likely that we simply don't know how physics works at the temperature and density that the universe was in, and a new, more accurate theory is needed.

Your claims are either too vague to be meaningful or just wrong. Observed (empirical) space-time curvature is close to zero (flat). We get very good agreement with our theories assuming space is flat but expanding.
We know NOTHING about 10E-43 seconds after creation. The fact is our theories EXTRAPOLATE to zero time, and there is no good reason to assume that the extrapolation is correct, just as there is no good reason to assume it is not. IOW, there may have never been a creation event, or it may have occurred at a time much different than that which we assign it. What we DO know is that various parts and pieces begin to make sense after cosmic inflation. Inflation is currently considered a result of a scalar potential field, which has no experimental evidence supporting it. (As opposed to inflation, which has a single report of B-mode polarization consistent with it). We have no theories I am aware of that allow more than 1 (or less than 1) time dimension.
I have no idea what you mean when you claim that time and space distinction is only empirical. This seems to me to be more nonsense. Please give me a single example of an emprical observation of space which includes no duration or just as good, give me an empirical observation of time with no spatial extent?
Planck time is 5.3E-44 seconds. Our theories fail long before this (on a logarithmic scale). What you should consider is the temperature at the time in discussion, and compare that temperature to the temperatures we are able to attain at the LHC. You should also consider the proportion of the Universe's energy we do NOT understand (dark energy, inflaton field, dark matter,...) and if that doesn't lead you to conclude that worrying too much about times before ~10^-18 sec is a fools errand, then good luck to you.

bapowell
(As opposed to inflation, which has a single report of B-mode polarization consistent with it).
This is a little restrictive. Superhorizon correlations in the EE spectrum, and adiabatic, Gaussian, nearly scale invariant perturbations are also consistent with inflation.

George Jones
Staff Emeritus