What if all human currently become immortal? Those who lived at particular fraction of time gain immortality and newborn don't have it .
So the ages of people on earth currently will become constant and are going to stay forever. The new born can grow up to produce normal humans. But the immortal population will stay constant .
The immortal will still need food as usual.
How to calculate food consumption and with every day increasing population under this scenario?
**Note:* What happens to immortal if they do not eat is irrelevant. Assume that they will still need to eat.