If you cannot hear a dog whistle, does that mean there is no sound coming from it? If you cannot hear the normal conversational low sounds elephants make, or if the equipment to measure the sound did not exhist yet, does that mean it cannot be heard or does not exhist?
Just because one does not have the ability to observe or sense something does not mean that it cannot or is not happening. If the value of our money has gone backwards, why not "time?"