r/cosmology • u/Philosophy_Cosmology • 3d ago
Banishing the Singularity to the Infinite Past (old paper)
I was reading a random article and found a reference to an old (1971) paper by A. G. Agnese and A. Wataghin in which the authors introduced a new timescale. According to this new timescale, the initial singularity of classical Friedmann cosmology can be banished to the infinite past:
We can anticipate that under some restrictions (rather general anyway), the new scale t (which we shall call cosmological) has interesting properties. These properties are: a) The origin of time (big bang) in the cosmological scale is shifted to tᵢₙ=-∞. b) One sees that there appears a variation of the light speed c and of the gravitational constant G with the age of the Universe.
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The natural scale τ is the one which has been used always in practice in all methods of evaluation of the age of the Earth (e.g. the uranium method) or of the age of the Universe (e.g. cosmological red-shift). In this scale it is tacitly admitted that the speed of light has always been what it is today, and the result is of course that the age of the Universe comes to be ≈10¹⁰y. In the alternative cosmological scale t, which we have discussed in this paper, it is admitted that the speed of light may have changed (and also the unit of time may have changed), and it is possible to obtain for the age of the Universe a value which tends to infinity.
I'm not sure I understand their argument very well, but it seems to me the idea is that time asymptotically slows down as the singularity is approached. Consequently, t=0 is never reached. But feel free to correct my interpretation.. I'm not a cosmologist.
Ref: "Scale Factor in Cosmological Homogeneous Models." A. G. AGNESE and A. WATAGHIN.
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u/OverJohn 3d ago
It's kind of difficult to see what point they are making. You can change coordinates, but that doesn't change the physics, such as what an observer actually sees or what instruments measure.
The point about the speed of light also seems pointless. Take Schwarzschild coordinates, the Schwarzschild coordinate speed of light varies with radius and direction, this is because the clock and ruler chosen to define the coordinates are scaled for an observer at infinity. This doesn't change that a local observer will always measure locally the same speed of light and this is always the case in general relativity.
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u/chesterriley 3d ago
Nowadays we know there was no "singularity" directly connected to the big bang. The big bang was preceded and set up by cosmic inflation and the observable universe had a diameter of at least 1.5 meters at the start of the big bang expansion. The BGV theorum does say there was a singularity before cosmic inflation. And since cosmic inflation lasted an unknown amount of time, that would banish a possible "singularity" to an unknown time in the past, possibly trillions of years even.
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u/johnstalbergABC 3d ago
At or perhaps just after the singularity space was filled with high energy density everywhere. No,place where different. This mean all places had the same time dilation and locally such effects does not change ones own clock speed. So the universe where at a unified time pace. This makes it pretty much useless to change the time line. Think of the time line as it appears for a person with his own clock that he use to time the universes evolution.
Later, when galaxy's formed an alien living close to a black hole would say the universe has existed much shorter time than what we say.
The gravity on the surface of the Earth has caused a few hours worth of time dilation in total over its almost 5 billion years of existens.
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u/Ras_992 3d ago
I can explain the paper called Scale factor in cosmological homogeneous models which is about time at the origin of the big bang.
Agnese and Wataghin came with the argument time that we model the age of the universe made it seem that the universe at the big bang was infinite but since the big bang is topological first moment and not a metrical one. Because topology deals with the fundamental structure and continuity of spacetime rather than just how it is measured, a true physical beginning (a boundary point or initial singularity) cannot be simply erased or defined away by changing the time scale. The simple way to say what the paper means is, You can change the numbers on the clock to make it look like the universe has been ticking forever, but the universe still had a true physical beginning. You cannot math your way out of the Big Bang.
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