We are still here. Public Science continues into the new year, but with a moderate and welcome change. This week we have a submission. Fulfilling both Elliot Tebboth’s role and theirs, they have provided both the question and answer.
Why should we believe the big bang happened? What is the evidence?
The ‘big bang’ theory does not address what existed before the ‘bang’ and provides no comment as to how it was initiated or indeed why.
The only thing supported by evidence is that the universe began in a minute, dense, energetic state approximately 13 billion years ago and has been expanding and changing ever since.
The first piece of evidence is based around the observation that if something is moving away from you, the electromagnetic waveform will be elongated.
In the case of light it would exhibit a shift to the red end of the spectrum or a redshift. Redshift has been observed in the light from galaxies, and is more pronounced in those further away.
This evidence indicates that the galaxies are moving away from us at an increasing rate, and that space itself is expanding.
The second piece of evidence comes from galaxy maturation. The distance to galaxies can be estimated using its brightness, through the ‘inverse square law’. When something is further away, it appears less bright by a predictable factor.
When looking at galaxies that are further away the light reaching us is older, and we see the galaxies in a less mature and more historic state.
This supports that the universe is not just expanding, but evolving.
These two pieces of evidence combine to indicate unequivocally that the universe is expanding and developing over time.
Therefore the assertion is that at a point in history it must have been smaller – much smaller.
The third major piece of substantiation is from old calculations that produced predictions. Predictions which have now been proven correct.
The first relates to the proportion of hydrogen and helium in the universe.
If the universe did start as raw energy which cooled to form elements it was deduced that hydrogen would make up 75% and helium 25%. A result which is now considered as confirmed by subsequent assessments.
The second surrounds the presence and temperature of the energy left over from the big bang itself. An estimation was made to predict the exact temperature and wavelength of the residual energy from the big bang after the passage of over 13 billion years.
The presence of energy with the predicted properties is now considered detected as the cosmic background radiation. These calculations made before they could be proved now help to confirm the nature of the big bang itself and the age of the current universe.
There are many more aspects that add to the evidence and informed opinion is that there is no other theory that fits the story so far.
However for the current model to work it does require the unproven existence of dark matter to hold it together and dark energy to push it apart.
The scientific world is waiting if you have a better idea.
The final verdict:
Thanks for this, Alan. It’s clear to me, and leaves a lot of interesting space for the discussion of why or how. As for which of us owes the other a pint, who’s to say? As ever, if you have any questions, or indeed answers, please email us. We’d love to hear from you.
Have an idea for our staff to tackle? Email us at firstname.lastname@example.org with the subject line “Pub Science”